Recognition of Two Distinct Groups of Human IgM and IgA Based on Different Binding to Staphylococci.

Labeled monoclonal IgM was bound to the Cowan I strain of Slaphylococcus arueus in the absence of anti-IgM antibody. This binding was inhibited by 11 of 33 monoclonal IgM proteins; 22 failed to inhibit. Agammaglobulinemic serum also failed to inhibit. High concentrations of IgG inhibited the binding of IgM Se to staphylococci, but IgG and IgM probably react with different receptors on the bacterial surface. Polyclonal IgM from all of 17 individuals tested inhibited the binding of IgM Se to staphylococci, which indicates that the distinction corresponds to an IgM subclass rather than to an allotype. Two of seven monoclonal IgA proteins also inhibited the binding of IgM Se to staphylococci. [ABSTRACT FROM AUTHOR]