Immunoglobulins of colostrum--VI. Comparative studies of cytophilic properties of bovine serum and colostral IgG.

In our previous studies, using physical-chemical and serological methods, substantial differences between bovine serum and colostral IgG, especially IgG2, have been shown. The structural differences were localized in the Fc region of immunoglobulins studied. The present comparative studies were undertaken to determine whether structural differences in the Fc region of bovine serum and colostral IgG are reflected in the interaction of these immunoglobulins with the guinea-pig peritoneal macrophage Fc gamma receptor. It was found that binding of bovine serum and colostral IgG1 was a saturable process and only quantitative differences in the mode of binding to the Fc receptor were observed. There is, however, a big difference in cytophilic activity of bovine IgG2--no saturable and reversible binding is observed in the case of bovine serum IgG2.