Immunochemical Properties of the Cross-Reactions between Anti-BSA and Heterologous Albumins

Abstract

Summary The immunochemical properties of the cross-reactions of 11 mammalian serum albumins with rabbit anti-BSA were investigated. The degree of the cross-reactions, as measured by precipitation, ranged between 5 and 75%. Nonmammalian albumin showed no cross-reaction with rabbit anti-BSA. In general, the initial combining ratios and the combining ratios at equivalence were lower with the heterologous reactions than with the homologous reaction. The precipitation curve obtained with the heterologous albumins showed the typical zones of excess antibody, equivalence and excess antigen. When I131 trace-labeled heterologous albumins were added to anti-BSA, virtually all of the I* activity was precipitated in the zone of excess antibody. The reaction between BSA and anti-BSA after absorption of the anti-BSA with sheep albumin gave a lower initial combining ratio and a lower ratio at equivalence than before absorption. The addition of an extreme excess of heterologous albumin to anti-BSA previously absorbed with the same albumin, failed to inhibit markedly the precipitation of the remaining antibody by BSA. Only 2 to 14% more cross-reacting antibody could be detected by an inhibition test than could be detected by direct precipitation. Studies employing absorption techniques, inhibition tests and double diffusion in agar, demonstrate that the cross-reactions between heterologous albumins and anti-BSA result from a sharing of certain related or identical determinant groups which represent only a portion of the total determinants present on the molecules. With absorption techniques and double diffusion in agar, it was shown that most heterologous albumins contain two or more serological types of determinants which crossreact with anti-BSA. Pepsin degraded BSA was shown to contain at least four serologically distinct determinants.