Active Immunization

Active immunization consists of the single or repeated introduction into the animal's body, parenterally or into the intestines, of killed or live causative agents of disease and their products (toxins, autolysates, various products of chemical processing of bacterial cultures, etc.). Expanding the concept, active immunization can be defined as the introduction into an animal's body of any substance possessing antigenic properties (see Antigens). The blood serum of animals immunized in this manner acquires the ability to give specific reactions with its antigen, such as agglutination, precipitation, binding of alexin (complement), toxin neutralization, etc., and the animal's body acquires increased resistance to that infection whose microbe (or its derivatives) served for immunization. Active immunization is contrasted with passive immunization, when the animal is injected with serum obtained from another actively immunized animal. Thus, in the first case, the animal's body itself participates in the development of immunity, whereas in the second it receives it passively along with the serum of another animal. Accordingly, active immunity requires for its development a more or less prolonged time—from several days to several weeks and even months (as for example, in immunization with a mixture of diphtheria toxin with antitoxins), whereas passive immunity appears immediately with the injection of the serum into the general bloodstream. The second difference is that active immunity persists for a long time—from several months to many years—depending on the properties of the material used for immunization and the infection itself, whereas passive immunity lasts only 3-6 weeks and precisely as long as the injected immune serum remains in the blood in sufficient concentration. With repeated introduction of immune serum, the duration of passive immunity decreases each time, reaching only several days. Furthermore, with repeated serum administration, especially of foreign serum, there is a danger of anaphylactic shock (see Anaphylaxis). Local active immunity, as shown by Besredka and some other researchers, does not always accompany the appearance in the animal's serum of specific reactions to the antigen, because in this case the struggle and protection of the body are limited to a specific territory and are carried out with the help of local formed elements, mainly the reticulo-endothelial system. Active immunity remains even after the disappearance from the serum of its specific reactive properties. This is explained by the fact that an actively immunized body is capable of responding to repeated irritation by the corresponding antigen or, what is the same, to new penetration of infection into it by rapid restoration and even enhancement of the specific reactive properties of its serum to these (antigen or infection). The concept "active immunization" encompasses the concept "vaccination." This term has become more widespread in recent years, when, to confer immunity to certain infectious diseases in humans, toxins detoxified by the addition of antitoxic serum or by chemical and physical means began to be used. Such is active immunization against diphtheria with mixtures of toxin and antitoxin and toxoids (see Anatoxin) or active immunization against scarlet fever with toxins, anatoxins or the so-called combined vaccine, composed in certain proportions from killed streptococci and streptococcal toxin. The same type should include immunization against tetanus and against various anaerobic causative agents of wound infections with toxoids (anatoxins) or with mixtures of toxins and antitoxins. In connection with the increasingly widespread use of active immunization, the question of the possibility and significance of Wright's "negative phase" has become particularly relevant. Depending on how it is resolved, the attitude toward active immunization in foci of infection is determined. Namely, according to Wright's hypothesis, the introduction of antigen, especially in large doses, reduces the content of antibodies in the blood of a given individual and thereby weakens his resistance to infection and consequently increases the chances of infection. Similarly, it was assumed that when antigen is introduced during the incubation period, the disease may take a more severe course. However, Wright's conclusions, based on observations of changes in the opsonic index during vaccination, have not been confirmed by epidemiological observations. Thus, the very existence of the negative phase in the sense as interpreted by Wright remains hypothetical. Consequently, it must be recognized that the presence of an epidemic is in no way a contraindication to active immunization, which is very important, because otherwise its application would be very limited and we would lose this most important means of combating epidemics at the most crucial moment.

S. Korshun.