Incompatibility between C3b and B of guinea-pig and man and its influence on the titration of the alternative pathway factors D and B in these two species.
The incubation of the proteins C3b, B, D and C3 induces enzymatic activation of B and of C3. This system of purified components was applied to the titration of the guinea-pig and human factors D and B in various homologous and heterologous reaction mixtures. On the basis of functional as well as of immunological tests, the D enzymes of both species were found to be related proteins. First, titrations of factor B revealed that both D enzymes activate homologous and heterologous B with comparable efficiency. Secondly, a rabbit anti-D antiserum raised against guinea-pig D was found to form a precipitation line of partial identity with guinea-pig and human D. In contrast to the compatibility between heterologous D and B, heterologous combinations of C3b and B were found to be incompatible. This incompatibility  was indicated by low titres of D in the presence of heterologous C3b and B; in contrast, in the presence of homologous C3b and B, the titres of D were up to one hundred-fold higher. The reason for this effect was found to reside in inefficient complex formation between heterologous C3b and B. Therefore titrations of D and B should be only performed in the presence of homologous C3b and B.
D000818:Animals; D000941:Antigens; D001797:Blood Protein Electrophoresis; D003176:Complement C3; D003165:Complement System Proteins; D003429:Cross Reactions; D000939:Epitopes; D006023:Glycoproteins / Q000097:blood; D006168:Guinea Pigs; D006801:Humans; D006867:Hydrolases; D009500:Neutralization Tests; D011485:Protein Binding; D012712:Serum Globulins; D015054:Zymosan
D000941:Antigens; D003176:Complement C3; D000939:Epitopes; D006023:Glycoproteins; D012712:Serum Globulins; D003165:Complement System Proteins; D015054:Zymosan; D006867:Hydrolases