Modulation of IgM to IgG class switch by protein A.

Abstract

The Fc binding property of soluble protein A (SpA) from Staphylococcus aureus has been utilized to form IgG-SpA complexes which enabled an increase or decrease of IgG from the host depending on the dose of SpA administered. When 5 micrograms SpA was administered the IgG-SpA complexes were rapidly catabolized and, hence, low plasma IgG levels were observed. In contrast 25 micrograms SpA resulted in a significant increase in the IgG level in the host plasma. Based on these observations, the present investigation attempted to study the effect of IgG depletion/increase on the primary and secondary B-cell response to sheep erythrocyte (SRBC) antigen in Balb/c mice. Introduction of 5, 10 and 25 micrograms SpA at the time of the primary antigenic challenge inhibited both the primary IgM and the secondary IgM and IgG responses in a dose-dependent manner. Administration of 5 and 10 micrograms SpA at the time of the secondary antigenic challenge enabled the host to maintain the otherwise depressed secondary IgM response equivalent to the normal primary response. In contrast, 25 micrograms SpA at the time of the secondary antigenic challenge inhibited both the IgM and IgG PFC responses. These results extend our understanding of the mechanism of switch in immunoglobulin class expression during antigen driven maturation of the B-cell response.