title: [Problem of J-chain of immunoglobulins].
abstract: Molecules of secretory immunoglobulins (Ig) of classes A and M (sIgA and sIgM) play the main role in protection of mucosae from pathogenic factors. The apparatus of synthesis of these molecules represents the most powerful part of the immune system. One of the key elements of the sIgA and sIgM is J-chain. It represents an acid polypeptide of molecular mass of about 15 kDa composed of 137 amino acid residues including 8 cysteine residues and one site of N-glycosylation. The primary structure of the J-chain is unique: attempts to ascribe it to any family of known proteins so far have failed. The J-chain is inserted into the sIgA and sIgM molecules to form disulfide bonds with C-terminal sites of alpha- or mu-chains. It is necessary for formation of IgA dimers and IgM pentamers, for reception of these molecules by epithelial cells, binding of secretory component to them, and for transfer of sIgA and slgM molecules onto mucosal surfaces and into secrets of endocrine glands. The J-chain has been revealed in the cytoplasm of the early T- and B-lymphocyte precursors not producing Ig. The J-chain is detected in the human embryonic liver cells earlier than the expression of the mu-chain gene begins. Study of mice with knockout of J-chain B-lymphocytes-producents has shown their block of function of T-helpers providing formation of immunologic memory. Comparison of J-chain genes of mammals, amphibians, reptiles, and cartilaginous fishes has shown the degree of interspecies homology of these proteins to vary from 33% to 70%. The J-chain genes were revealed in representatives of all vertebrate classes except for cyclostomes and bony fishes. In 1996, data were published about the presence of the J-chain genes-homologs in invertebrates, tunicates, and cyclostomes. No papers reproducing or confirming these data have been published. On the contrary, in the literature an opinion appeared that indicate necessity to revise the notion about the presence of J-chain in invertebrates. The main unsolved issues on the J-chain involve the tertiary structure of this protein, its relation to some particular protein family, its functions in cells of the T- and B-lymphocytic differentiation lineages as well as its evolutionary age.
authors.forename: V B
authors.initials: VB
authors.lastname: Klimovich
authors.forename: M P
authors.initials: MP
authors.lastname: Samoĭlovich
authors.forename: B V
authors.initials: BV
authors.lastname: Klimovich
mesh_terms: D000818:Animals; D019281:Dimerization; D004220:Disulfides / Q000276:immunology; D006031:Glycosylation; D006801:Humans; D007070:Immunoglobulin A / Q000235:genetics / Q000276:immunology*; D007144:Immunoglobulin J-Chains / Q000235:genetics / Q000276:immunology*; D007075:Immunoglobulin M / Q000235:genetics / Q000276:immunology*; D007137:Immunoglobulin alpha-Chains / Q000235:genetics / Q000276:immunology; D007148:Immunoglobulin mu-Chains / Q000235:genetics / Q000276:immunology; D054503:Lymphoid Progenitor Cells / Q000276:immunology; D009092:Mucous Membrane / Q000276:immunology; D020836:Protein Structure, Quaternary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology
chemical_list: D004220:Disulfides; D007070:Immunoglobulin A; D007144:Immunoglobulin J-Chains; D007075:Immunoglobulin M; D007137:Immunoglobulin alpha-Chains; D007148:Immunoglobulin mu-Chains