Characterization of the lymphocyte membrane receptor for factor H (beta 1H-globulin) with an antibody to anti-factor H idiotype.
Antibody to the binding site (idiotype) of anti-factor H was shown to have specificity for both B lymphocyte membrane H receptors and C3b. Goat F(ab')(2) anti-human H was purified by absorption and elution from H agarose and used for rabbit immunization to produce anti-anti-H (aaH). After absorption with nonimmune goat IgG, (125)I-labeled aaH bound to B lymphocytes and to sheep erythrocytes coated with C3b (EC3b) but did not bind to T lymphocytes or to EC3d. All B cell- and C3b-specific activities of the aaH were removed and subsequently recovered by absorption and elution of the antibody from either C3-agarose or goat-anti-H-agarose. This indicated that the aaH probably recognized a single common antigenic structure that was shared by anti-H, C3b, and the membranes of B cells. Affinity-purified aaH resembled H in that it bound to B cells, blocked the uptake of H onto B cell H receptors, and triggered B cells to release endogenous factor I (C3b inactivator). In addition, aaH functioned with factor I as either a cofactor for cleavage of fluid-phase C3b or a potentiator for cleavage of bound C3b. This same spectrum of C3 binding functions could not be demonstrated with either sheep anti-C3b or rabbit-anti-C3c. Analysis by sodium dodecyl sulfate- polyacrylamide get electrophoresis of the [(3)H]leucine intrinsically labeled B cell proteins reactive with the purified aaH revealed proteins of 100,000 M(r) and 50,000 M(r) without reduction, and after complete reduction of disulfide bonds, a single protein band of 50,000 M(r). This same protein molecular weight profile was also demonstrated with labeled B cell proteins that were absorbed and eluted from H-agarose. Thus, aaH is apparently specific for both B cell H receptors and C3b. However, because parallel analysis of C3b confirmed its known 115,000- and 75,000-M(r) polypeptide chain structure, the H receptor is probably not C3b and shares only the structure of the H binding site with C3b.
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D000918:Antibody Specificity; D001666:Binding Sites, Antibody; D001667:Binding, Competitive; D002460:Cell Line; D003179:Complement C3b / Q000276:immunology; D003180:Complement C3b Inactivator Proteins / Q000276:immunology / Q000494:pharmacology*; D017242:Complement Factor H; D006041:Goats; D006801:Humans; D007130:Immunoglobulin Idiotypes / Q000276:immunology*; D008565:Membrane Proteins; D008970:Molecular Weight; D011817:Rabbits; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*
D000888:Antibodies, Anti-Idiotypic; C493495:CFH protein, human; D003180:Complement C3b Inactivator Proteins; D007130:Immunoglobulin Idiotypes; D008565:Membrane Proteins; D011947:Receptors, Antigen, B-Cell; D003179:Complement C3b; D017242:Complement Factor H