immunity

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The quality or condition of being immune.
2. n. Immunology Inherited, acquired, or induced resistance to infection by a specific pathogen.
3. n. Law Exemption from normal legal duties, penalties, or liabilities, granted to a special group of people: legislative immunity.
4. n. Law Exemption from legal prosecution, often granted a witness in exchange for self-incriminating testimony.

Century Dictionary and Cyclopedia

1. n. Exemption from obligation or responsibility in any respect, conferred by law or a sovereign act; freedom from legal liability; an exemption conferred, as from public service or charges, or from penalty for any particular act or course of conduct; hence, special privilege; liberty to do or refrain from doing any particular thing.
2. n. Exemption from any natural or usual liability.
3. n. In eccles. usage, the exemption of certain sacred places and ecclesiastical personages from secular burdens and functions, and from acts regarded as repugnant to their sanctity. This immunity is of three kinds:
4. n. See the quotation.
5. n. In pathology, a lack or absence of susceptibility to disease. This may be either natural or acquired. Natural immunity may be of the most varied character. Thus it is found that animals are altogether insusceptible to many diseases which are common in man, such as yellow fever, smallpox, scarlet fever, measles, etc.; the cold-blooded animals, as a class, are free from many diseases which are common in the warm-blooded animals; birds and reptiles are exempt from tetanus, mice and rats from diphtheria. Again, children are much more prone to certain diseases (as measles, scarlatina, diphtheria, etc.) than adults. Certain individuals appear immune against diseases to which others of the same species readily succumb. A familiar example of acquired immunity, on the other hand, is that which follows an attack of yellow fever, or smallpox, typhoid fever, scarlet fever, etc. Immunity of this character, which depends upon actual infection, is called active immunity, since the body itself is active in its production. This is in contradistinction to passive immunity, which is referable to the introduction of protective substances from without. Such immunity is seen, for example, following protective injections of diphtheria antitoxin. Knowledge regarding the essential factors which are operative in the production of immunity to disease is still very defective, but many points have been worked out from which a general idea of the process can be formed. Through the researches of Ehrlich and his pupils in Germany more especially, and of Metchnikoff and Bordet in France, besides many others, the concept of immunity has been materially amplified; for it has been shown that the animal body has a mechanism of self-protection which is of the most extensive character and is directed not only against the harmful effects of bacteria but also against all alien cellular elements and cell-products of whatever kind, in so far, at least, as these latter are of an albuminous character. Thus it has been ascertained that the injection of certain soluble toxins leads to the production of corresponding antitoxins, as in diphtheria, tetanus, botulism, and poisoning with certain vegetable toxins, as ricin, abrin, crotalin, etc. Similarly, the introduction of various tissue-cells of an alien species leads to the formation of corresponding cytolysins or cytotoxins, such as hemolysins, leucolysins, neurolysins, endotheliolysins, spermatolysins, and so on apparently without limit. Then, again, it was shown that the injection of certain cells calls forth the production of corresponding agglutinins, which cause the clumping or coalescence of the cells in question. Various albuminous substances similarly lead to the production of bodies which, when brought together with the first, cause the formation of precipitates—the precipitins. There are also the coagulins, which result on injection of certain albumins; the antiferments; and so on. Thus it is seen that the introduction into the body of almost any foreign substance of an albuminous character (antigen) is followed by the production of a corresponding antagonistic or antibody. It is accordingly necessary to extend the meaning of the term immunity to include the general defensive reaction on the part of the body to the action of foreign cellular elements or their constituents. As regards the mechanism by which the various antibodies are formed and immunity is accordingly produced opinions differ, but there is a general tendency to accept the explanation offered by Ehrlich and his pupils, which is based upon the now famous lateral-chain theory (see below). The general study of immunity has led to a vast amount of experimental research, and to results of the utmost practical importance. Thus the discovery of diphtheria antitoxin has furnished a cure for one of the most fatal diseases to which man is subject. Tetanus is now successfully combated by an antitetanin. Snake-bite poisoning, which in India is annually responsible for many thousands of deaths, is readily amenable to specific treatment in a large percentage of cases. Antirabic treatment has lowered the fatality percentage of rabies to nearly one per cent. In many other diseases to which man is subject altogether satisfactory antisera have not as yet been developed, but a certain degree of protective immunity can be established in some, as in plague, typhoid fever, and dysentery. In these cases immunization is effected by means of attenuated cultures of the corresponding organisms. Of vast economic importance is the successful immunization of certain animals against diseases which would otherwise prove highly fatal, as of sheep against anthrax and of cattle against rinderpest. Important from the standpoint of prophylaxis, also, is the possibility of promptly recognizing the existence of tuberculosis in cattle by the injection of tuberculin, and, to judge from recent reports, it now seems possible also to immunize actively against the disease in question. Ehrlich's lateral-chain theory, upon which the modern doctrine of immunity is largely based, explains better than any other the various experimental data that have been elaborated within recent years. According to it, the living cell contains a formative central nuclear complex, the Leistungskern of Ehrlich, to which other molecular groups, the so-called side-chains or receptors, are united. Through the union of food material with these side-chains the nutrition of the cell is maintained. Through these same side-chains, however, the cell is also open to attack by the most diverse foreign agents, provided that the chemical constitution of the latter is analogous to that of the usual food material of the cell, or, as Ehrlich puts it, provided that the deleterious agents possess groups, or haptophores, which will fit the receptors of the cell. Ehrlich recognizes three varieties of receptors, which he classifies as belonging to the first, the second, and the third order. Those of the first and second orders contain only one combining group for the alien material, which is to act upon the cell; for this reason they are termed uniceptors: while the receptors of the third order have two combining groups and are called amboceptors. In the case of the receptors of the second and third orders the alien material, antigen or immunizing body, as it is generally termed, is capable of producing its specific effect upon the cell only in the presence of a ferment-like substance which must be especially supplied, as the so-called complement in the case of receptors of the third order, while in those of the second such a complex represents an integral component of the receptor (the zymophoric group). If, now, a foreign substance of a harmful nature effects a union with some of the receptors of a cell, these receptors are practically lost to the cell. In accordance with Weigert's overproduction theory, this loss, unless the cell has been injured beyond the possibility of recovery, is then not only made up by the production of other receptors of the same kind, but an overproduction occurs. The supernumerary side-chains are thrown off, and now circulate in the blood in the free state. In this condition they are known as haptines, and, like the original sessile receptors, they may be of the first, second, or third order, as already described. As their presence in the blood in the free state prevents the access of foreign cellular products to the cell, these haptines are antagonistic in their action to that of the alien material, and thus constitute true protective bodies. For this reason they are termed antibodies, or adaptation-products, the latter term indicating that they are formed as a result of an effort on the part of the body to adapt itself to the presence of the foreign substances. The sera in question are similarly known as antisera or immune sera. Upon this basis natural immunity is readily explained by the assumption that receptors corresponding to the infecting agent are lacking, so that an attack upon the cell is impossible. Acquired immunity, on the other hand, is the result of infection and the consequent formation of antibodies. It may be antitoxic or bactericidal in nature, according to the character of the infecting agent. Antitoxic immunity is thus far known to develop in only three conditions, namely, in diphtheria, tetanus, and botulism. Bactericidal immunity, in contradistinction to antitoxic immunity, depends upon the production of more complicated antibodies, namely, haptines of the third order (amboceptors, immune bodies, etc.), in which a coaction of a ferment-like complement is necessary to produce the specific effect. Passive immunity depends upon the introduction of specific antibodies from without, and can also be of the antitoxic or bacteriolytic type, according to the nature of the substances employed.

Wiktionary

1. n. uncountable The state of being insusceptible to something; notably.
2. n. countable A resistance to a specific thing.

GNU Webster's 1913

1. n. Freedom or exemption from any charge, duty, obligation, office, tax, imposition, penalty, or service; a particular privilege
2. n. Freedom; exemption.
3. n. The state of being insusceptible to disease, certain poisons, etc.

WordNet 3.0

1. n. the quality of being unaffected by something
2. n. an act exempting someone
3. n. the state of not being susceptible
4. n. (medicine) the condition in which an organism can resist disease