[Asymmetric IgG antibodies. Structural, immunochemical and biological studies]

Studies of our laboratory have shown that the coprecipitating antibodies are IgG molecules which possess an asymmetric structure due to a carbohydrate group present in only one of the Fab regions of the molecule. The combination of the corresponding antibody site with antigen is sterically hindered by the carbohydrate group, and as a consequence, the molecule is functionally univalent. As no aggregation of the antibody takes place, effector immune mechanisms such as complement fixation, phagocytosis, clearance of antigen, etc. are not triggered. However, since nonprecipitating antibodies can firmly combine with antigen, they act in a competitive way when they are mixed with precipitating antibodies of the same specificity. It has been demonstrated that hybridomas synthesize both symmetric and asymmetric molecules indicating that precipitating and nonprecipitating antibodies are elaborated by the same cellular clone. Nonprecipitating antibodies do not precipitate the antigen but they are able to agglutinate sheep red blood cells sensitized with the specific antigen. Because red blood cells of sheep and of many other animal species possess a membrane receptor for aggregated Fc, agglutination of sensitized sheep red cells by nonprecipitating antibodies is a consequence of a mixed mechanism in which one Fab and the Fc fragment of the IgG molecule participate. In animals immunized with soluble antigens, the nonprecipitating antibody represents 10-15% of the total. Higher concentrations have been observed when the inoculated antigen is particulate. In cows infected by B. aortus and in humans infected by T. cruzi, the percentage of nonprecipitating antibody ranges between 30-70% of the total antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)