[Adaptive significance of the limited gene expression of the immune system]. / Ob adaptivnom znachenii ogranichennoi ékspressii genov immunnoi sistemy.

Evolutionary development of immunity multigene systems seems to involve host-parasite molecular coevolution, as evidenced by comparison of metasoans and unicellular organisms in fixation rates of neutral and adaptive point mutations per one pair of corresponding genes. The estimations we attempted revealed that organisms with maximal restriction of Ig-like gene repertoire expression by an individual immune cell are more adaptive in formation of competent antigen-induced immune response, provided that the magnitude of potential repertoire of functional Ig-like receptors exceeds lymphoid cell population size. In contrast, when phage and bacteria populations are in coevolution, there is no need to limit the repertoire of expressive genes encoding bacteria surface receptor proteins which are recognized by a phage adsorption system. Other hypotheses of evolutionary premises and stimulus of immune genes expression limitation (allelic, isotypic etc.) are critically discussed.

[Theoretical analysis of the correspondence between the stages of evolutionary divergence and the functioning of multigene families of the immune system]. / Teoreticheskii analiz sootvetstviia mezhdu étapami évoliutsionnoi divergentsii i funktsionirovaniia mul'tigennykh semeistv immunnoi sistemy.

By means of phylogenetic comparison of main immunoglobulin-like multigene families (MF) and of different C-domain sequences representing them, the order of divergences of these MF in the process of evolution of the system was analysed. The order proved to be in good agreement with the ordered fashion of MF's involvement into recombinational rearrangements during the immune cell development. Indeed, according to topology of the tree for 34 C-domains, all MHC antigens are separated from the rest of Ig-like sequences, at first. Secondly, beta-chain of T-receptor is branched off the main stem of divergences, then there is a serium of divergences of CH-domains for different Ig-classes, and at last, kappa- and lambda-chains are separated. It is mu-chain of IgM which first of all branched off within an each group of isofunctional CH-sequences in the tree (CH1, CH2, CH3, CH4). The same order of events could be seen in ontogeny of the immune system. The results suggest that the appearance of a new MF of Ig-like type (or a new cluster of genetic segments within the MF) in the course of evolution could mean the addition of a new step in the regulatory system of immunologic gene expression already involved. In other words, this is unique example of recapitulation at the molecular-genetical level.