Immune system

“ T lymphocytes: also called T cell. They are an important type of lymphocytes that maintain the immune system and are essential to fight against pathogenic microorganisms. There are two main types of T lymphocytes, Cytotoxic T cell (Tc) and the T helper cells (Th) . The Tc look for antigen infected cells in the body. When a Tc recognizes an antigen bound to a cell, it adheres to the surface of the infected cell and produces toxic molecules, killing the cell. ”

“ Finally, a secondary stain (safranin) is added and Gram-negative bacteria will appear pink.
Immunological memory: it is the ability of rapid immune response against an agent that already had contact with the immune system. ”

“ The migration reduces the viral presence in other parts of the body, with a corresponding diminution in physical manifestations of the disease. The virus, however, thrives in the lymph nodes, which, as a vital point of the body's immune response system, represents an ideal environment for the infection of other CD4‘ cells. ”

“ Suffice it to say, that various scientists have learned that immunity may be produced in a previously susceptible animal by the injection of various preparations. But in each instance, the injection is expected to produce immunity from only one disease. My own studies were at first in this direction, and I have succeeded not only in learning how to prevent each malady separately, but what is far better, I have discovered a method by which I can render an individual immune to all zymotic diseases. ”

“ In passive immunity the blood serum of an actively immunized animal is introduced into a second animal, which thereupon becomes immune, though its cells are not concerned in the process. The animal is passive, just as a test-tube, in which a reaction takes place, plays no other part than that of a passive container for the reagents.
In active immunity the organism may be introduced in what is to be considered a natural manner, as when an animal becomes infected, has a disease, without human interference. Or the organism may be purposely introduced to bring about the immunity. ”

“ It has been found that immunity from disease may be acquired by young animals being suckled by a female which had previously become immune, the antibody to the disease being absorbed in the ingested milk. ”

“ But acquired immunity, possessed by an individual residing among a people who are susceptible, is the problem of greatest interest. The difference between a susceptible and an immune animal depends upon one fact. In the former, when the disease-breeding germ is introduced, it finds conditions favoring its multiplication, so that it makes increasing invasions into the tissues. The immune animal resists such multiplication, and possesses inherent powers of resistance which finally exterminates the invader. But how can this immunity be acquired by a given individual? ”

“ It is a fact that if the serum of an animal which has been rendered immune to a certain disease be injected into a susceptible animal, the same immunity can be produced temporarily in the second animal. ”

“ In fact, as he ascended the scale of beings and studied their natural and artificial immunity, he ascertained that, in all of them, the essence of immunity, masked by the complexity of the organism, reduced itself to the phagocytes becoming accustomed to noxious agents. The mechanism of immunity in protozoa could therefore really be compared with that of immunity in multicellular beings.
Becoming accustomed and becoming immune are phenomena of a general order, for they can be manifested not only by animals, but also by plants. They, too, have to defend themselves against numerous diseases. ”

“ One thing seems, however, to become more and more certain—namely, that the serum of the blood of immune or vaccinated animals, although in many cases it does not destroy the microbes themselves, is nevertheless possessed of a vaccinating power. ”

“ I desire now to refer again to the subject of racial and species immunity for which the humoral factors of bacterial destruction afforded an imperfect explanation, in order that I may point out that the introduction of bacteria, incapable of causing infection, into immune species is followed by immediate phagocytic ingestion and destruction of the microorganisms. The rapidity and perfection of the phagocytic reaction in insusceptible animals are very impressive and might readily lead to the decision that they suffice to explain the resistance or immunity. ”

“ In general, the innate and acquired immune responses are not activated independently. Their optimal performance is when they complement each other.
In particular, the AIS’ antibodies are able to direct the IIS’ components toward the relevant objects. ”

“ To be able to resist the invasion of any species of bacteria, one is said to be refractory to or immune against that variety of germs.
Serum therapy is based on the demonstrated fact of immunity, and of the possibility of producing it by injecting the serum of immunized animals. In many infectious diseases, one attack protects an individual for a lifetime and one form of disease may protect against even a more virulent form, as vaccination protects against smallpox. ”

“ The child that sleeps in the open and eats an abundance of pure, wholesome foods and takes a proper amount [Pg 85] of exercise, will escape most of the diseases of infancy and grow into manhood with a body immune to almost every infectious germ. I need not go into detail in regard to the actual mechanism of immunity to prove the fact that a well-nourished body, sustained by blood of high nutritious power and bearing its untold millions of organisms, armed cap-a-pie to destroy intruders, is a sufficient illustration of immunity. ”

“ This conclusion is not justified, as we must suppose that the process of immunization begins to be developed at an early period in the disease, that it gradually increases, and ultimately results in cure. It should also be stated that agglutinins are used up in the process of agglutination, apparently combining with some element of the bacterial structure. In view of all the facts it must be admitted that the agglutinins and immune bodies are the result of corresponding reactive processes, and are probably related to one another. ”

“ Immunity may be acquired in several ways. It is commonly known that one attack of certain communicable diseases renders the individual immune for a varying length of time, and sometimes for life. Among these diseases are smallpox, measles, whooping-cough, scarlet fever, infantile paralysis, typhoid fever, chicken-pox, and mumps; erysipelas and pneumonia on the other hand appear to diminish resistance and to leave a person more susceptible to later attacks. ”

“ The increased ingestion of bacteria in active immunity would seem to depend upon the presence of immune opsonins in the serum. These, as already explained, are true anti-substances. Thus the apparent increased activity of the leucocytes is due to a preliminary effect of the opsonins on the bacteria. We have no distinct proof that there occurs in active immunity any education of the phagocytes, in Metchnikoff’s sense, that is, any increase of the inherent ingestive or digestive activity of these cells. ”

“ Many animals have natural immunity to certain diseases; they do not have the disease under natural conditions, nor do they acquire the disease when the organisms causing it are artificially introduced into their tissues by inoculation. Such natural immunity seemed to be unconnected with defence by phagocytosis, for the leucocytes of the animal might or might not have phagocytic reaction to the particular organisms to which the animal was immune. It was also seen that recovery from infection in certain diseases was unconnected with phagocytosis. ”

“ Ordinary cleanliness, good vitality, clean blood and tissues, the organs of elimination in good, active condition and, last but not least, a positive, fearless attitude of mind will practically establish natural immunity to the inroads and ravages of bacteria and disease taints. If infection takes place, the organism reacts to it through inflammatory processes, and by means of these endeavors to overcome and eliminate microorganisms and poisons from the system. ”

“ The process by which passive immunity is acquired depends upon the fact that as a result of the reaction between the specific virus of a particular disease (the antigen) and the tissues of the animal attacked, certain substances—antibodies—are produced, which when transferred to the body of a susceptible animal protect it against that disease. The most important of these antibodies are the antitoxins. From the study of the processes by which immunity is secured against the effects of bacterial action the serum and vaccine methods of treating certain infective diseases have been evolved. ”

“ Since the neutralizing materials are different for different infections, immunity against one is in most cases of no avail against another. One may be immune against scarlet fever, but be just as likely to catch pneumonia as a person who has never suffered from any infection at all. ”

“ Immune body or amboceptor is the name given to a substance present in the serum of an infected animal that has successfully resisted inoculation with some particular micro-organism, and which possesses the power of linking the complement normally present in the serum to bacteria of the species used as antigen in such a manner that the micro-organisms are rendered innocuous, and ultimately destroyed. ”

“ Immunity may be natural or acquired. By [14] natural immunity is meant an inherited characteristic by which all individuals of a species are immune to a certain disease. The natural immunity of certain species of animals to the diseases of other animals is well known. Man is immune to many diseases of lower animals, and they in turn are immune to many diseases of man. Cattle, for instance, are immune to typhoid and yellow fever, while man shows high resistance to rinderpest and Texas fever; both, however, are susceptible to tuberculosis, to which goats are immune. ”

“ If these germs, however, are conveyed to another person, who has never had the disease, or whose tissue is not immune, they will immediately resume their full activity and virulence, and will establish the disease, frequently in its most violent form, in the person so infected. ”

“ The theories of immunity rest upon the assumption of the presence of some proteid body in the blood which endows the whole system with powers of resistance to toxins. Exhaustion, especially such as is induced by the emotions, fatigue, grief, anger and fear, are well known to weaken the protective power of these mysterious agencies. ”

“ Diseases which produce a general infection of the whole system are, as a rule, more likely to give rise to a lasting immunity than those which affect only small parts. Tuberculosis, which, as already noticed, is commonly quite localized in the body, has little power of conveying immunity, while a disease like scarlet fever, which affects the whole system, conveys a more lasting protection. ”

“ The question of the value of preventive inoculation is, however, still an open one. So also are other applications of the principles of immunity, as the production of anti-sera for snake-venom, and for the irritant (and perhaps intoxicating) vegetable agent causing hay fever.
I have earlier in this lecture referred to methods of serum diagnosis depending on agglutination or solution of bacteria or on the precipitation of protein. Immunology has recently contributed to medicine another diagnostic method of great value. ”

“ Incidentally we have discovered from this process of mixed or conjoint vaccination that immune sera prepared for bacteria or other parasites which are not toxin producers in the manner of the diphtheria bacillus, but which contain endotoxin, act not especially by neutralizing toxins, or by destroying outright the bacteria, but by exercising an efficient protective control over the injury which these parasites or their poisons tend to inflict on certain sensitive body cells. ”

“ In fact, one of our newest and most reliable tests for the disease consists in a curious "clumping" or paralyzing power over cultures of the Bacillus typhosus, shown by a drop of the patient's blood, even as early as the seventh or eighth day of the illness. And, while it is an immensely difficult and complicated subject, we are justified in saying that this immunity is not merely a substance formed in the body, the stock of which will shortly become exhausted, but a faculty acquired by the body-cells, which they will retain, like other results of education, for years, and even for life. ”

“ Ways of detecting adulteration in foods, particularly foods from animal sources, and of differentiating proteins of varied origin, as well as means of establishing biological relationships and differences among groups of animals through “immunity reactions” of blood serums have followed from knowledge gained by application of the facts or the methods of immunity research. Hence the study of “immunity problems” has come to include much more than merely the study of those factors which prevent the development of disease in an animal or result in its spontaneous recovery. ”

“ By immunity is meant non-susceptibility to a given disease, or to experimental inoculation with a given bacterium or toxin. The term must be used in a relative sense, and account must always be taken of the conditions present. Immunity.An animal may be readily susceptible to a disease on experimental inoculation, and yet rarely or never suffer from it naturally, because the necessary conditions of infection are not supplied in nature. That an animal possesses natural immunity can only be shown on exposing it to such conditions, this being usually most satisfactorily done in direct experiment. ”

“ Doubtless, also, some of the gland cells in the body have a corresponding action; statements which, if true, tend to emphasize the possible proteid nature of the protective substances.
While in a general way we may say that the natural immunity to certain bacteria possessed by some animals is due in large measure to an inhibition of the growth of the micro-organism, it must also be remembered that there is in many species a distinct immunity to the action of the poison which the specific micro-organism produces. ”