7.32 On the Present State of the Question of Immunity in Infectious Diseases
Mechnikov
Nobel Lecture
Nobel Lecture, December 11, 1908
I am here before you by virtue
of paragraph 9 of the Statutes of the Nobel Foundation, which states that
"it shall be incumbent on a prize-winner, whenever this is possible, to
give a public lecture on a subject connected with the work for which the prize
has been awarded, such a lecture to be given within six months of Commemoration
Day, in Stockholm".
I have had the great honour of
receiving, together with my excellent friend, Professor Ehrlich, the Nobel
Prize for Medicine "for work on immunity", so that it is on this
subject that I shall speak. Since the study of immunity is a chapter in medical
theory, and theory is often hard to expound to an audience unequipped with the
special notions implied, you see the difficulty that lies before me.
Fortunately, the theoretical problem on which I shall enlarge concerns the
resistance of the body the disease. Whatever concerns health is of real public
interest. I take advantage of this to make my address less arduous for you. I
shall moreover use the opportunity to show you the practical value of pure
research.
There is no need to be a doctor
or a scientist to wonder why the human body is capable of resisting so many
harmful agents in the course of everyday life. It is often seen that in
households where all members are exposed to the same danger, or again in
schools or troops where everyone lives the same life, disease does not strike
everyone indifferently. For some individuals who go down at the attack, there
are others who have immunity to a greater or lesser extent.
There used to be only a vague answer to the problem of the body's resistance,
remarkable as it is. Since the memorable discoveries of Pasteur and his
co-workers who found that immunity could be conferred by means of vaccination
with microbes, the question has all at once become vastly clarified. The
problem has become open to study by experiment. For Pasteur, who was a chemist,
the fact that the undamaged organism does not allow certain morbid agents to
spread within it, could be explained simply in terms of the chemistry of the
environment. In the same way that plants will not grow on soil that lacks some
substance indispensable to their growth, so microbes, these microscopic plants
which cause infectious disease, are unable to grow in an organism which does
not give them all the substances they need.
This theory is completely
logical but contradicted a number of factors to be found in the protected
organism. Pasteur and his fellow workers realized this themselves when they
found that infectious microbes develop very well in the blood of animals that
enjoy complete immunity.
The animal organism is very
complex and for this reason it is often hard to explain in simple concepts the
phenomena to be observed. To achieve the purpose, a different approach has had
to be called for. It has been necessary to look from the point of view of
biology, and attempt to simplify research conditions without going beyond the
scope of the living organism. This is the idea that has been behind our
research. Disease is not the prerogative of man and the domestic animals, so it
was quite natural to see if the lower animals, with very simple organizations,
showed pathological phenomena, and if so, infection, cure and immunity could be
observed among them.
To solve medical problems,
comparative pathology had to be called in.
While studying the origin of
the digestive organs in the animal world, we were struck by the fact that
certain of the organism's elements which have no part to play in the digestion
of food are nevertheless capable of storing foreign bodies. For us, the reason
was that these elements had once been part of the digestive system. This
question of pure zoology has no further place here, so we will only stress the
general outcome of our research in this field, which was that the elements of
the organism of man and the animals, gifted with autonomic movements and
capable of enveloping foreign bodies are no more than remains from the
digestive system of primitive beings.
Certain of the lower animals,
transparent enough to be observed alive, clearly show in their midst a host of
small cells with moving extensions. In these animals the smallest lesion brings
an accumulation of these elements at the point of damage. In small transparent
larvae, it can easily be shown that the moving cells, reunited at the damage
point do often close over foreign bodies.
Such observations on the one
hand confirmed our assumption on the origin of these migrant elements, while on
the other they suggested that accumulation round lesions is a sort of natural
defence on the part of the organism. Some method had to be found by which this
hypothesis could be verified. I was at this time - more than twenty five years
ago - in
Sharp splinters were introduced
into the bodies of these Bipinnaria and the next day I could see a mass of
moving cells surrounding the foreign bodies to form a thick cushion layer. The
analogy between this phenomenon and what happens when a man has a splinter that
causes inflammation and suppuration is extraordinary. The only thing is that in
the larva of the starfish, the accumulation of mobile cells round the foreign
body is done without any help from the blood vessels or the nervous system, for
the simple reason that these animals do not have either the one or the other.
It is thus thanks to a sort of spontaneous action that the cells group round
the splinter.
The experiment I have just
outlined shows the first stage of inflammation in the animal world. Now
inflammation as understood in man and the higher animals is a phenomenon that
almost always results from the intervention of some pathogenic microbe. So it
is held that the afflux of mobile cells towards points of lesion shows the
organism's reaction against foreign bodies in general and against infectious
microbes in particular. On this hypothesis, disease would be a fight between
the morbid agent, the microbe from outside, and the mobile cells of the
organism itself. Cure would come from the victory of the cells and immunity
would be the sign of their acting sufficiently to prevent the microbial
onslaught.
This deduction, based on the
fundamental experiment with the splinter in Bipinnaria, had to be checked by
observations and specific experimentation. Luckily for us, it is not only man
and the higher animals that are subject to infectious diseases. These diseases
existed on the earth long before the appearance of the human race and few are
the creatures which escape them.
Therefore, to demonstrate the
value of the hypothesis I have mentioned, some higher animal was needed, small
and transparent enough to be observed living under the microscope and yet
subject to microbial disease.
Several starts were made. It
became possible to study the progress of infection in fresh-water animals,
commonly known as "water-fleas". These small crustaceans abound in
all kinds of stagnant water and are subject to various diseases. One is caused
by a tiny microbe characterized by the production of spores in the shape of
needles. Swallowed by the water-fleas or Daphniae, which is the scientific
term, these spores readily damage the intestinal wall and penetrate to the body
cavity. Once they have insinuated themselves into the organism's inmost part,
the spores cause an accumulation of the mobile cells round them, which
correspond to the white corpuscles in human blood. A battle takes place between
the two elements. Sometimes the spores succeed in breeding. Microbes are
generated that secrete a substance capable of dissolving the mobile cells. Such
cases are rare on the whole. Far more often it happens that the mobile cells
kill and digest the infectious spores and thus ensure immunity for the
organism.
This description is from a
living animal and can be observed at each stage under the microscope with such
precision as could hardly be bettered.
The results obtained from the
larvae of starfish and from disease in water-fleas form the bedrock of the
theory that I am here to expound. This theory came under heavy fire from the
greatest names in science and there was some doubt that such an attack was to
be withstood. The memory of the Bipinnaria and the splinter surrounded by
mobile cells and the Daphniae with their blood corpuscles devouring the
dangerous spores of the infectious microbe, these gave me hope to fight on.
Controlled observations on living organism can not be wrong.
Having established the base of
the theory of immunity, it had to be applied to the higher organisms and even
to man himself. Conditions were incomparably more complex than in the little
transparent creatures, and difficulties arose on all sides. Given the
impossibility of submitting a vertebrate, even the smallest such as a new-born
mouse, to direct examination by microscope, a more complicated way had to be
taken, by combining the results of research on the blood and organs extracted
from the organism, and thinking out the interconnection. In such circumstances,
the door is wide open to mistakes of all sorts.
The study of various infectious
diseases in man and the higher animals showed first that the facts observed
corresponded very satisfactorily with the theory based on research on the
lower, transparent animals. Whenever the organism enjoys immunity, the
introduction of infectious microbes is followed by the accumulation of mobile
cells, of white corpuscles of the blood in particular which absorb the microbes
and destroy them. The white corpuscles and the other cells capable of doing
this have been designated "phagocytes", i.e. devouring cells, and the
whole function that ensures immunity has been given the name of
"phagocytosis".
It has been established as a
general rule that in all cases of immunity, natural or acquired, either by
preventive vaccination or following an attack of infectious illness,
phagocytosis takes place to a marked degree, whereas in fatal or very dangerous
diseases, this phenomenon does not exist at all or is attenuated. This rule was
demonstrated for the first time on animals immunized against anthrax. When the
anthrax bacillus is injected under the skin of sensitive animals, such as the
rabbit or the guinea-pig, the microbe is found free in abundant fluid from
which the white corpuscles are almost wholly absent. When however the same
inoculation is carried out on a rabbit or a guinea-pig that has been previously
vaccinated against anthrax, a very different picture results. The bacilli are
within a short space of time seized by the white corpuscles which accumulate in
quantity at the inoculation point. Once inside the phagocytes, the bacilli die
within a comparatively short time. It happens on occasion that only a few hours
after the absorption of the bacilli by the white corpuscles, the bacilli are
dead.
In time the same rule has been
extended to cover a whole host of other infectious diseases. Every time the
organism enjoys immunity, the infectious agent falls prey to the phagocytes
that gather round the microbes. This general law has even been verified by
studying pathogenic microbes, discovered since the law was formulated. With
plague, in all cases where the organism is refractory, the plague bacillus is
devoured and destroyed by the phagocytes, while in fatal cases of plague the
majority of the microbes remain free in the organism's fluids and multiply
without hindrance.
To date we have found no
exceptions worthy of note to this rule. It is true Weil of Prague has
maintained in several publications that in cases of immunity regarding the
cholera microbe in hens, the refractory organism meets the microbial invasion
by other means than phagocytes. He bases his case on the impossibility of
finding this microbe inside the white corpuscles in animals that are resistant
to illness. This exception is not a true one. It is explained by the minute
dimensions of the cholera microbe in hens, owing to which it easily eludes the
eye of the beholder. Soulima examined this question very thoroughly in my
laboratory and he found it to be true that, in accordance with the general law,
in animals refractory to the cholera bacillus of hens, it is again the white
corpuscles that take hold of the microbe and cause it to disappear within
themselves.
Opposers of the phagocyte
theory have long taken the view that the white corpuscles and phagocytes in
general are only capable of absorbing microbes that have first been killed by
the humours of the organism, namely blood plasma and exudative fluids. It would
today be hard to find anyone who still maintains this view. Many accurate
experiments have shown that the phagocytes surround the infectious microbes
while these are quite alive and in a condition where they are capable of
bringing fatal infection to the organism that does not enjoy immunity.
The results which I have thus
summarized have been achieved after many a long year of research and
discussions. Many scientists still kept to the old idea, that the white
corpuscles represent an element hostile to health. In serious illness,
collections of pus used to be met with. This was thought to consist of white
corpuscles only, as the microbes were too small to be detected by the imperfect
tools of microscope research. It was supposed that the pus corpuscles
themselves might be the source of disease found in the morbid alteration of our
cells. When later microbes came to light inside the white corpuscles, it was
admitted that the corpuscles, as ill-omened elements in our body, only serve to
feed and spread the body's worst enemies, namely the agents of infection. The
destruction of these in cases of immunity was rather attributed to the direct
influence of the organisms's fluids.
The theory of the bactericidal
action of the humours was brought in against the phagocyte theory. To the
organism enjoying immunity, natural or acquired, was attributed the power of
destroying the infectious microbes without any real assistance from the live
cells. This affirmation was based on well-known instances, in which blood and
blood serum taken from the organism proved able to kill a considerable quantity
of infectious microbes. This theory of the humoral immunity met multiple and
major contradictions from the outset, yet it was not without ardent support.
The discovery of Pfeiffer was of great assistance to the theory, for he
demonstrated the destruction of cholera vibrios in the humour of the abdominal cavity
in animals immunized against this microbe. This case has become classic. The
vibrios do not die within the phagocytes but in the fluid of the peritoneal
secretion. Every attempt was made to show that this was not a case of an
exception to the rule, but the demonstration of a general law of immunity. But,
after years of hard research, it has been conclusively shown that the vast
majority of infectious microbes can not be destroyed by the liquids of the
organism and that the instance of the vibrios is to be explained by their
extreme fragility. It was also maintained that the destruction of the vibrios
by the humours took place by means of the bactericidal substances released by
the white corpuscles present in the abdominal cavity. In cases where the very
microbes had been introduced to regions of the organism where there were no
white corpuscles already in existence, then the destruction of the vibrios was
done within the phagocytes which came on to the field of battle. Even in the
abdominal cavity, the extracellular destruction of the vibrios was easily to be
avoided if the white corpuscles were prevented from suffering and thus from
spreading their bactericidal substances. This experimental observation was
denied by many observers over a period of years. It was however conclusively
confirmed some years back by Bail of Prague. It has thus been clearly shown
that as long as the white corpuscles are intact, the destruction of vibrios in
the organism that has immunity takes place within the phagocytes.
Thorough analysis of the
phenomena of immunization, an analysis based on extremely numerous experiments,
has shown that phagocytosis is in truth a defence action on the part of the
organism against the agents of disease. Several of the former supporters of the
exclusively humoral theories of immunity later came round to the cellular
theory, with more or less important reserve, however. So various intermediate
theories were adduced, according to which the organism, threatened by microbial
onrush, brought all its resources into play: phagocytes and humours. For some,
the destruction of certain infectious agents in the cases of immunity was by
the organism fluids, especially the blood plasma, while other microbes had
greater resistance and were only killed within the phagocytes. This eclectic
theory was developed in the main by your compatriot, A. Pettersson.
For this defence action, the
organism would make use of two classes of bactericidal substances, one of which
would be circulating in the blood fluid and flow thence to the exudations
formed round the microbes, while the other group would only be found within the
phagocytes. The first category would react first and foremost on the cholera
vibrio, typhoid bacilli and their congeners, while the other would destroy anthrax
bacilli, suppuration microbes and others as well.
Just as there were two diverse
bactericidal functions of the organism, so the nature of the substances that
destroy the microbes would be diverse. The bactericidal substances of the
humours would be of complex nature, consisting of a substance that would
prepare the microbes, without damaging them, for the action of the substance
that would kill them. Various names were put forward to designate these two
substances. Ehrlich gave the name of amboceptor to the preparatory
substance and the name of complement to that which destroys the
microbes. Not to complicate further matters that are very complicated already,
we shall use the terms proposed by our eminent colleague, without sharing his
view of the actual part played by the two substances.
Formerly, I mean to say ten
years and more ago, certain scientists thought that the bactericidal substance
proper, although circulating in the blood fluid, was nevertheless a secretion
of the white corpuscles. Of late more and more voices state the contrary to be
the case. It is readily admitted that the complement has nothing to do with the
corpuscles and has a completely different origin. This view is based on much
research carried out with extracts prepared from the white corpuscles taken out
of the organism. To this end, exudations that are very rich in these corpuscles
are used. They are washed to rid them of liquid parts and then they are killed
by subjecting them to cold and letting them macerate in physiological fluid. In
the extracts of white corpuscles obtained in this way, no complements are found
capable of destroying microbes. This is established, for it has been checked
and counterchecked on innumerable occasions. It is not however correct to
conclude on this account that the white corpuscles do not produce the
complement.
To form an opinion on this much
discussed topic, Levaditi and I began to study the bactericidal properties of
white corpuscles. First of all we found that these cells, taken from the organism,
are indeed capable of absorbing and destroying many microbes. Making use of
Deneke vibrios, that resemble the microbes of Asian cholera, we were able to
show quite easily their transformation into granules in the interior of the
white corpuscles of guinea-pigs. This transformation, which takes place very
fast with vibrios impregnated with the amboceptor or preparatory substance,
implies their destruction. The white corpuscles must therefore contain in their
components a substance which acts just like the complement of the humours. Now
let us see how the substance behaves in fluids deprived of this bactericidal
substance but having a large quantity of white corpuscles possessing the
complement. One has only to keep these elements for twenty hours to discover
that at the end of that time they have become completely incapable of
transforming the vibrios charged with the amboceptor. The corpuscles have had
time to die for the most part and in these circumstances the vibrios remain
intact.
We have repeated this
experiment several times with the same result, thus showing that the complement
in the white corpuscles is a very fragile substance. It is beyond doubt that
the long operations of washing, cooling and maceration of the white corpuscles
are destructive for the complement, by and large. That is why this method must
be rejected in studying the bactericidal substances in white corpuscles.
Do not think that as the action
of the complement is only manifest while the white corpuscles are alive, this
is purely a vital phenomenon. On the contrary it is most likely that this is a
chemical action which alters according to the state of the white corpuscles.
Here is an analogous example which will support this view.
The magnificent masses of
living matter to be found in certain mushrooms known as "Myxomycetes"
are capable, like the white corpuscles, of enveloping foreign bodies and
digesting them inside the vacuoles. These are filled with acid juice which
favours digestion and whose function is readily demonstrable by giving the
living matter some blue litmus particles to absorb, which in a short time turn
pink. Well, without killing the living protoplasm, it is enough to bruise it by
pressing lightly, and the grains turn blue again. The reason is that the living
matter is full of alkaline substance which straightway, at the least shock,
penetrates into the juices of the vacuoles and neutralizes the acid in them.
This is an example of purely chemical reaction, closely linked to the being and
well-being of living matter.
It may be asked why the action
of the complement is so fleeting in the white corpuscles, when it lasts much
longer in the humours taken from the organism, such as blood serum. We believe
the difference to lie in that the white corpuscles, over and above the
complement, contain an anti-complement substance as well which prevents the
action of the complement, just as the myxomycetes besides the acid juice
contain alkaline substances.
Without going into more
thorough analysis of this question, we can state that the white corpuscles are
microscopic organisms that are more complex than they appear at first sight and
that to deal with them in the mass to make extracts is almost as rough a method
as squeezing whole animals, say mice or frogs, to find out their digestive
powers.
As a result of research which
we can do no more than outline to you in summary fashion, we still hold that
the complement of the humours comes from the white corpuscles. When the white
corpuscles suffer a faint attack, they only release the complement into the
fluids in which they are immersed. When however the white corpuscles are
subject to more serious lesion, a substance is released which neutralizes the
action of the complement. We can quote as evidence to support this opinion that
in the immunized organism, where the white corpuscles are intact, vibrios do
not undergo the granular transformation in the humours and only take granular
form in the interior of the white corpuscles.
Our plea is one of identity,
for the complements contained in phagocytes and for those in blood serum. Are
there, besides the complement, other substances capable of destroying microbes,
substances exclusively and intimately linked to the white corpuscles? This
question has as yet no ready answer, owing to the technical difficulties
involved. It is likely, as appears from the research carried out by Pettersson
and others, among whom we mention Max Gruber and his assistants, that
substances of this kind, the endolysins of Pettersson or the leukins
of Schneider, do exist in reality.
Quite apart from this intricate
problem of the nature of microbicidal substances in the organism, it has been
clearly shown that the power of the humours to kill infectious agents is
restricted to the weakest microbes, also that the microbicidal part played by
the white corpuscles and the phagocytes in general holds good for all
infectious agents from which the body can have immunity.
As stated above, the
bactericidal action of the complements is closely linked with another category
of substances, the amboceptors of Ehrlich. They can not destroy nor damage the
agents of disease. The amboceptors fasten on the agents and help the
bactericidal action of the complements. The complements are localized in the
phagocytes, whereas the amboceptors are to be found in the humours of the
living organism and pass with ease to the fluids that accumulate round the
microbes. Indubitably these are humoral substances that participate in the
process of immunity. But the amboceptors are nothing else than phagocytic
products excreted in the other fluid surroundings. Various researchers have
established that the sources of the amboceptors are the spleen, bone marrow and
lymphatic ganglia, in other words the very organs which are filled with
phagocytes. It has even been shown by the experiments of Wassermann and Citron
that the amboceptors arise in the places where infectious microbes have been
introduced, places invaded by vast hordes of white corpuscles.
At the beginning of these
investigations on the amboceptors, it was thought that the substances took part
in the destruction of the microbes, but were completely alien to the system of
phagocytic defence. Later it became clear that as products of the phagocytes,
the amboceptors were only one of the terms of this defence.
The mechanism of the action of
the amboceptors on microbes is not known in detail, not being manifest. In
fact, the infectious agents impregnated with the amboceptors go on living and
reproducing at the normal rate. They even keep their pathogenic power, but
become capable of undergoing the action of the complements and more prone than
before to be seized and enveloped by the white corpuscles.
In the case of the most fragile
microbes, such as cholera vibrios and their kind, the combined action of the amboceptor
and the complement leads to the destruction of the bacteria, whether
accompanied or not by the granular transformation. But the great majority of
pathogenic agents give greater resistance to a mixture of these two substances,
as obtained in the organism or outside it in blood serum. In this case, there
can be no question of bactericidal action as it is usually understood. But the
microbes, impregnated with the amboceptor and the complement, fall an easy prey
to the white corpuscles. The mixture of the two substances serves most of all
to prepare the phagocytosis. Because of this characteristic, it has been called
opsonin by Wright and bacteriotropin by Neufeld.
Persuaded of the relative
unimportance of the humours as destructive agents to infectious microbes, the
followers of the humoral theories have lately fallen back on the opsonins and
the bacteriotropins, considered as humoral factors well to the fore in
immunity. Not being able to do any damage at all to the microbes, they only
modify them in so far as their absorption by the phagocytes are facilitated.
Wright, who has been largely responsible for developing this argument, insists
on the subordinate role of the white corpuscles that follow blindly the opsonin
lead. He even judges the progress of immunity and cure according to the opsonic
strength of the blood fluid. But, insisting on the preparation of the morbid
agents by the opsonins, Wright admits the virtue of the phagocytes in ridding
the organism of microbes. He even goes so far as to admit the existence of a
spontaneous phagocytosis, which evolves without the aid of the opsonins. The
opsonins would be important, however, in making the action of the white
corpuscles more speedy and more sure.
It is a priori probable that
the phagocytosis, namely the swallowing and digestion of the microbes by the
phagocytes, is subject to favourable influences in the organism. Is not in
intestinal digestion the secretion of the pancreatic juice favoured by other
elements like secretin? There is thus no objection in principle to the theories
of Wright and Neufeld. Only the methods on which the theories are based do tell
against them. All research into opsonins and bacteriotropins has been conducted
with humours and white corpuscles extracted from the organism and mixed with
the microbes in glass test tubes. This method, which is very demonstrative,
cannot render adequate account of the phenomena in the living body. The fate of
the bactericidal theory of humours, based on experiments in vitro, should serve
as a warning against placing too much trust in results obtained under these
conditions. If it is true, as a great number of research workers now hold, that
the opsonins and the bacteriotropins are mixtures in varying proportions of the
complements and the amboceptors, one could easily understand that in the living
organism things go on in quite another way than in test-tube experiments. We
have already stressed the fact that the complements are linked to the
phagocytes and only break away in exceptional circumstances.
In the investigations on the
opsonins and bacteriotropins, investigations guided by humoral notions, on the
whole only the power of the blood fluid to favour phagocytosis is regarded. The
white corpuscles are taken as constant elements which can only obey the behests
of the opsonins. Now the white corpuscles are living organisms, hypersensitive
to external conditions and which admit of very great variation. The least
change in the salt content of the fluid which surrounds them is enough to bring
about significant modification of the phagocytosis. The white corpuscles of
patients attacked by different diseases show a real diminution of their vital
characteristics. The work of Parvu on the cells taken from a patient suffering
from myelogenic leukemia showed more than half of the white corpuscles
powerless to absorb the microbes.
Faced with such facts, some
scientists stress the need to study not only the opsonic property of blood
fluid but also to take into account the phagocytic function of the white corpuscles
themselves. This idea is justified in so far as the destruction of the microbes
is the main purpose of the organism's fight against the agents of disease.
This destruction is carried out
by live strong phagocytes. The absorption of the pathogenic bacteria, helped by
the opsonins, is important but it is only the beginning of a series of
phenomena that culminates in the digestion of the microbes within the
phagocytes. In case the microbes that have been absorbed by the white globules
do not die, owing to a deficiency of bactericidal substances, the organism is
short on its defences and falls victim to the infection. It can happen that
highly resistant microbes, such as the spores of tetanus bacilli, can be a long
while in the white corpuscles without causing the terrible illness. The moment
the corpuscles suffer some deleterious influence, for example cooling or
overheating, then the spores that were hitherto imprisoned are set free and do
straightway produce fatal tetanic cramps.
This is why, as several doctors
have already pointed out, the power of the opsonins is not enough of itself in
all cases to ascertain the organism's level of resistance.
The phagocytes, subjected to
influences favourable or unfavourable, have to reckon with the resistance of the
agents of disease in their fight against the microbes. It can happen that the
agents secrete substances which bring about deterioration in the white
corpuscles to the point of dissolving them altogether. But in most instances,
it is lesions which prevent the phagocytes absorbing and destroying the
microbes. The substances that are directed against the phagocytes have been
designated agressins by Bail. These are special poisons which attack the
phagocytes in particular. In order for our defence cells to do their job
properly, they must be protected against the microbial agressins. It has even
been maintained that salutary phagocytosis can only take place with the aid of
some preparatory action which is capable of neutralizing the agressins. This
action would take its origin from elements of the body alien to the phagocytes.
Series of experiments show that the white corpuscles are well fitted to absorb
the agressins, without the agressins undergoing any modification. The work of
Wassermann and Citron showed that the macerations of pathogenic microbes,
prepared outside the organism, give a product which when introduced into the
organism in quantity hinders phagocytosis. But these same microbes, generators
of these agressins, are easily absorbed by the white corpuscles when the latter
are in a state of reinforced activity.
The phagocytes are capable of
fighting not only the agressins, I mean microbial poisons that work on the
white corpuscles in particular, but even violent poisons that can kill the
organism. This is a fact of prime importance in the study of immunity. After
the wonderful discovery of bacterial counterpoisons by Behring, the opinion has been voiced that the defence of the
organism which enjoys immunity relies above all on the neutralizations of the
toxins, which are the poisons that the microbes produce. The microbes,
following neutralization, forfeit the spearhead of the attack on the organism
and descend to the level of absolutely harmless entities which in turn fall
easy prey to the phagocytes. Phagocytosis would thus, although acting on live
microbes, be reduced to an action of entirely secondary importance.
Numerous findings, achieved
with care over the last few years, clean contradict this view. It has been
shown that the white corpuscles entertain no fear of microbial poisons and are
well fitted to absorb them and make them harmless. This was best illustrated by
work on poisons in the body of infections microbes, going under the name of endotoxins.
Besredka's work is the most conclusive in this regard. He injected the
abdominal cavity of guinea-pigs with dead bacilli of typhoid fever that could
not cause the infection but contained typhoid endotoxin. The animals died
within twelve hours. The same injection was given to animals whose abdominal
cavity contained a large number of strong white corpuscles, and these took over
the microbial bodies and their endotoxin and thus saved the animal from certain
death.
Bail and Weyl got analogous
results using a staphylococci poison. Injected by itself, this poison kills
young rabbits within a matter of hours. Injected with a certain amount of white
corpuscles, this poison is inactive and the animals live on.
Such examples could be
multiplied. So it seems certain that the phagocytes do ensure immunity, not
only from infections microbes but also from poisons produced by these microbes.
Of all the organism's elements, the phagocytes are distinguished by their poor
sensitivity to toxicity. This is so true that white corpuscles are even able to
withstand poisoning by mineral poisons. When endotoxins were not so well known
and when the search for bacterial poisons soluble in the organism was fraught
with great difficulty, Besredka went into the question of protection afforded
by the white corpuscles with regard to arsenical preparations of small
solubility. He selected arsenic trisulphide, the crystals of which are absorbed
and modified by the phagocytes with avidity. He found that when the abdominal
cavity of guinea-pigs contained a great quantity of white corpuscles, these
cells saved the animals from fatal poisoning by phagocytising the crystals of
the arsenic trisulphide. Similar findings have since been established on many
occasions and it is now commonly held that many toxic and medicamental
substances, introduced into the organism, are to be found in abundance in the
interior of the white corpuscles. Lately Carles of Bordeaux has demonstrated
the absorption of lead salts by white corpuscles. These salts were absorbed
insoluble and became transparent within the phagocytes. When subjected to
hydrogen sulphide vapour, however, they at once turned black. In absorbing
poisons, the white corpuscles in their capacity as primitive elements
comparatively non-sensitive to toxins, preserve the noble cells, such as those
of the nervous system, the liver and other glands.
The sum of the very numerous
facts established in the archives of science leaves no room to doubt the major
part played by the phagocytic system, as the organism's main defence against
the danger from infectious agents of all kinds, as well as their poisons. Where
natural immunity is concerned, and man enjoys this in respect of a large number
of diseases, it is a question of the phagocytes being strong enough to absorb
and make the infectious microbes harmless. It goes without saying that the
phagocytic reaction is helped by every means at the organism's command.
Thus, when the microbes
penetrate, the white corpuscles make use of the dilatation of the blood vessels
and the nervous actions that control this, in order to reach the battle field
in the shortest possible time. Every influence that can trigger off the
phagocytosis is naturally brought to bear.
In immunity achieved as a
result of vaccinations or subsequent to an attack of the disease, the organism
shows a series of modifications. Much stress has been laid on the growth in
humoral properties under these conditions. In fact the blood fluid in these
cases contains considerable amounts of amboceptors and bacteriotropins (very
probably identical) which prepare the microbes for phagocytosis. But, as said
above, the amboceptors are products of the phagocytes. Now to secrete great
quantities in the humours, the phagocytes must be modified in the organism that
has acquired immunity. This might have been expected a priori but it has not
been easy to prove by conclusive evidence. Pettersson had the idea of
introducing white corpuscles into the organism, originating from animals that
had been vaccinated against certain microbes. He found that these elements do
give real protection against doses of infectious microbes that are fatal
several times over. On the other hand, the white corpuscles of an organism
which does not have immunity are powerless to produce this result.
Salimbeni, in view of the
outstanding import of this, began a series of experiments at the Pasteur
Institute, with the aim of checking Pettersson's findings. Using a method that
allowed of great accuracy, he was able to confirm these findings and take them
further. He showed that the white corpuscles of the immunized organism are a
true source of protective substances, and that at a time when the blood fluid
does not yet show any modification. In spite of successive washings, the
phagocytes still ensured immunity. In the course of his research, Salimbeni
proved that at the moment when the humours have already lost their protective
powers altogether, the organism is still refractory and resists fatal doses of
infectious microbes. This fact, together with other supporting evidence, leads
to a conclusion of the greatest importance. Namely, that even in acquired
immunity, the properties of the cells take pride of place over the humoral
properties.
At this point, it may seem
paradoxical that in spite of the serious modifications that follow acquired
immunity, the white corpuscles show no augmentation of their function which may
strictly be termed phagocytic. They absorb the infectious agents to the same
extent as the white corpuscles taken from a normal organism and put into
contact with the humours of the immunized organism. Ever since the first
experiments of Denys and Leclef, those concerned have stressed the importance
of this finding. It must not be forgotten that these experiments were conducted
with white corpuscles taken from the organism and studied in vitro. In spite of
all that has been said on this score, the objection is valid. Comparison is
drawn between phagocytosis of the white corpuscles of an organism that has been
subjected during weeks and months to injections of vaccine and all the while
kept captive, and the white corpuscles of a fresh organism which has never been
under attack. The conditions, as may be seen, are far from identical.
Even were it soundly established
that the phagocytes in acquired immunity do not undergo any modification, to
their power of absorbing microbes, this result would not in any way invalidate
the general fact of augmentation in the defensive power of the phagocytic
system. It need only be admitted in this instance that just as for acquired
immunity there is no augmentation found in the production of the complements,
so there is no augmentation in the property of enveloping. The strengthening of
the defence would then be reduced to overproduction by the phagocytes of
substances that prepare the way for phagocytosis.
The total of phenomena observed
in immunity thus reduces to a series of biological acts, for example the
sensitivity of phagocytes, their active movements directed to areas imperilled
by the microbes, and a series of chemical and physical acts which bring about
the destruction and the digestion of the infectious agents. Since a dozen
years, under the impulse provided by the theories of Ehrlich, many men of
science have tried hard to lay bare the inner mechanism of the phenomena of
immunity. Ehrlich himself held that the amboceptors, which abound in acquired
immunity, combine in determined proportions with the molecules of the
complements on the one hand and with those of the microbes, i.e. their
receptors on the other. Many field-workers, led by Bordet, fight this theory. According to them, the
amboceptors are unworthy of the name, for they are not the chemical go-between
of the complements and the microbes, but act on these like the mordant in
tissue dyeing. Bordet also calls amboceptors by the name of sensitizing
substances, on account of their property to facilitate the action of the complements
on the microbes. The whole phenomenon falls in his eyes into the category of
molecular absorption in varying extents.
The polemic on these two
theories has been going on ten years. The problem of the inner mechanism of
immunity is so delicate and complicated that it is not yet definitely resolved.
It must however be said that many research workers find it fashionable to
support the idea that the action of the organism on microbes is outside the
picture of chemical phenomena strictly so-called, and is rather in the domain
of the physical actions of the colloids, some of which spring from the microbes
while others belong to the organism. Analogies are sought between substances
that are observed in immunity and the colloids. Some are not far from saying that
the complements are lipoids, analogous to those that come in to the
constitution of animal organs.
All this research promises
results of prime importance in the more or less near future. At the moment,
what it amounts to is no more than incursions into a field thick with thorny
problems. The place of the phagocytic system in immunity has however emerged
from the stage of theory and is now doctrinal.
It is time to ask now if the
notions acquired from so many years' work and discussion yield practical application
in medicine. This general law that in all cases of immunity the phagocytic
reaction is pronounced, leads one to conclude that the degree of phagocytosis
can be used in medical prognosis. From the beginning of our research on
phagocytosis, we became convinced that the more the microbes were absorbed by
the white corpuscles, then the more chance the animal had of surviving and
making a complete recovery. Swiss veterinary expert, Zschokke, was the first to
make use of this rule in the struggle against infectious mammitis in cows,
which is an epizootic that causes serious deterioration in milk. He was able to
show that plentiful phagocytosis of streptococci, which are the disease bearers
of this sickness, is a good sign that all is going well. The fate of cows
suffering from "gelber galt", as mammitis is locally called, depends
on the extent of phagocytosis. When this is insignificant or nil, the cows are
written off as no longer productive of good milk. A whole system has been built
up to determine the degree of phagocytosis and this is confirmed by findings on
slaughtered animals. Although in most instances, the extent of the phagocytosis
gave a precise indication, examples have been known of cows which did not
recover although the majority of the streptococci was contained within the
white corpuscles. These exceptions in turn led to new field-work on the part of
Vrijburg. As was to be expected according to phagocytosis theory, for the
organism to triumph over the infectious microbes, these must not only be
absorbed by the white corpuscles but also utterly destroyed. There are cases
where the streptococci of mammitis, after absorption by the phagocytes,
demolish the cells and finish by being free to carry on their deadly work. To
arrive at sound prognosis, the extent of the phagocytosis must be measured and
the state of the phagocytes with the microbes within them must be known too.
This example of contagious
mammitis should admonish those who think it enough to determine the opsonic
strength to be able to judge how an illness or indeed immunity is faring.
In other diseases brought on by
streptococci, the degree of the phagocytosis can also serve as a prognostic.
Professor Bumm in
In the treatment of illness by
Dr. Wright's vaccinotherapy, the phagocytosis shows the opsonic strength of the
blood. It is thus a guide to the doctor. We said above that this method was
coming to be joined by that of determination of the property of phagocytes,
independently of the opsonic action in itself. For some time phagocytosis has
been used with success in the diagnosis of certain infectious diseases.
Among the practical
applications of the doctrine of phagocytosis mention must be made of the use in
surgery of substances capable of bringing a large quantity of white corpuscles
to areas under operation and open to infection. There are already surgeons in
Of the therapeutic methods that
have emerged latterly, we note the process of Professor Bier. This consists in
the systematic application of cupping-glasses and rubber strips to augment the
veinous stasis round abcesses, furuncles and similar afflictions of many kinds.
Cure is often achieved by this means with a rapidity that is little short of
surprising. It has been asked what caused such success. Modern methods of
research at their most refined have been used. The contradictions have not been
entirely removed. But it is generally held that the phagocytosis is an
important element in cure effected by the Bier method. The application of
cupping-glasses and bands causes veinous stasis and thus an oedema is formed
round the injured area. At the same time, a large number of white corpuscles
come to the spot, and these serve to strengthen the phagocytosis. In a very
recent treatise on this subject, the Japanese Dr. Schimodaira, working in a
European laboratory and with no particular love of the phagocytic theory, has
nevertheless been forced to admit that augmenting the phagocytic reaction in
the use of the Bier method is one of the main factors effecting cure.
It is small wonder after so much
evidence has been given on the valuable part played by the phagocytes, that
research should concentrate on the conditions capable of strengthening
phagocytic reaction. A number of works has recently been published on this
topic. Among the substances that activate phagocytosis, mention can be made of
quinine, a medicine much loved by medical practitioners. Grünspan's research
shows that weak solutions of two milligrams per hundred raise the power of
phagocytosis to a marked degree, while solutions fifty times stronger give the
opposite result. Neisser and Guerrini have studied a whole series of substances
that stimulate phagocytic activity, among which they make especial reference to
certain solutions of peptones. The chapter on stimulins that we opened a
long time ago and that had lain forgotten has recently been put back on the map
again. All means are used to augment the phagocytic reaction to ensure cure and
immunity. How different by far from the ideas that were once sovereign in
medicine. I remember forty years ago the famous Helmholtz having learned from
Cohnheim that the pus corpuscles in inflammation come from the white corpuscles
in the blood, taught, in accordance with the then current theories, that the
accumulation of such elements constituted a danger to the organism, a danger
that must be met by doses of quinine, capable of paralysing the movements of
the white corpuscles. It is enough to compare this point of view with the
actual concept of the benign role of the inflammatory reaction in general and
of the phagocytic reaction in particular, to gather how far we have come.
The theory of phagocytes, laid
down more than twenty-five years ago, has come under heavy fire on all sides.
It is only of late that it has won recognition from the well-informed in all
lands, and it is only as it were yesterday that it has begun to have practical
use. We have thus the right to hope that for the future medicine will find more
than one way to bring phagocytosis into play to the benefit of health.
I have attempted to outline the
present state of a subject that may serve as an example of the useful purpose
to be served by purely theoretical research. The study of the origin of the
digestive organs in the lower animals, since long disappeared, has opened up
the field little by little, leading to a new concept of immunity, to the quest
for methods of fighting infection and ensuring resistance and recovery, of the
organism.
In awarding me a prize for my
research on immunity, the Nobel Committee has chosen to honour me for all my
work done over twenty-six years, and in part carried out by my many pupils at
the Pasteur Institute.
I express my deepest thanks to
the Committee for this great distinction which gives me the greatest joy any
savant can wish for. I have however one fear. Namely that the Committee is
esteeming my work beyond its true worth. I take heart from the thought that it
was the intention of the generous founder Alfred Nobel to reward men of
learning who give their lives to knowledge without deriving any benefit from
its practical applications.
From Nobel Lectures, Physiology or Medicine 1901-1921,
Elsevier Publishing Company,
