Immunogenetics (redirected from immunogenetic)

Immunogenetics

A scientific discipline that uses immunological methods to study the inheritance of traits. Traditionally, immunogenetics has been concerned with moieties that elicit immune response, that is, with antigens (antigenic determinants). It has now broadened its scope to study also the genetic control of the individual's ability to respond to an antigen. See Antigen

The immunological methods used in immunogenetics are of two principal kinds, serological and histogenetical. In serological methods, antibodies are used to detect antigens, either in solution or on a cell surface. In histogenetical methods, immune cells (lymphocytes) are used to detect antigens on the surface of other cells. In modern immunogenetics research, the serological and histogenetical methods are combined with molecular methods in which the researcher isolates and works with the genes that code for the traits. This approach of going back and forth from classical to molecular methods has proved to be very successful and has led to the elucidation of several complex genetic systems. See Antibody

Animal immunogenetics relies heavily on the use of inbred, congenic, and recombinant inbred strains. Inbred lines result when individuals that are more closely related to each other than randomly chosen individuals mate together, for many generations. The advantage in working with inbred strains rather than outbred animals is that inbred strains restrict the variability of the conditions of an experiment. However, when two strains are compared and it is found that they respond differently to a treatment, it is not known to what gene this difference should be attributed. The strains may differ at as many genetic loci as two unrelated individuals in an outbred population do. To study the effect of single, defined genes, immunogeneticists have developed congenic lines. These lines always come in groups, the smallest group being a pair, which consists of a congenic line and its inbred partner strain. The two are homozygous at more than 97% of their loci (that is, they are inbred) and are identical except, ideally, at one locus—the locus that is to be studied. To find out whether two loci are on the same or on different chromosomes, two individuals that differ in the traits controlled by these loci are mated and then the F₁ hybrids are intercrossed. In the F₂, generation that results from this intercross, the genes assort either independently, if they are on different chromosomes, or nonrandomly, if they are the same chromosome—that is, when they are linked. Each time the strains are tested for linkage, this laborious procedure must be repeated. To avoid this repetition, immunogeneticists have prepared a “frozen” F₂ generation by establishing separate inbred lines from the different F₂ individuals. Such lines are called the recombinant inbred strains.

Contemporary immunogenetic research concentrates on two main categories of antigenic substances—those present in body fluids, primarily blood serum or plasma, and those expressed on surfaces of various cells. In the body-fluid antigens category, a prominent position is occupied by immunoglobulins. Although antibodies are usually used to detect antigens, they themselves may also serve as antigens, and antibodies can be produced against them. These antibodies against antibodies detect three principal kinds of antigenic determinants: isotypic, allotypic, and idiotypic. The main categories of cell-surface molecules studied by immunogenetical methods are blood-group antigens, histocompatibility antigens, tissue-restricted antigens, and receptors. Blood-group antigens are alloantigens found on erythrocytes. Histocompatibility antigens are antigens capable of inducing cellular immune responses and hence are detectable by histogenetical methods. Tissue-restricted antigens are expressed on some tissues but not on others and therefore serve as markers for cell sorting. Receptors are molecules that are capable of specifically interacting with certain other molecules. The interaction often leads to activation or inhibition of the receptor-bearing cell. See Blood groups, Genetics, Histocompatibility, Immunoglobulin, Immunology