Binding of Murine Myeloma Proteins of Different Ig Classes and Subclasses to Fc-reactive Surface Structures in Gram-positive Cocci

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Abstract
Twelve different murine myeloma proteins were tested for binding to 70 Gram-positive strains belonging to group A, C and G streptococci and to Staphylococcus aureus. Group A streptococci, known to bind human Ig[immunoglobulin]G, were incapable of binding any of 8 murine IgG Ig tested except for 1 strain that bound an IgG2b myeloma protein. Group C and G streptococci interacted with murine Ig of subclasses IgG2a, IgG2b and IgG3, and G strains also to a lesser extent with IgG1. Bovine and equine group C streptococci did not differ from human group C streptococci in their IgG reactivity. Staphylococcal strains showed high reactivity with murine myeloma components of IgG subclasses 2a, 2b and 3 and a low but definite binding of an IgG1 myeloma protein. IgA myeloma protein S-122 interacted with 9 of 15 group A streptococci. This binding could not be inhibited by human IgG and the reactivity is thus different from Fc-mediated binding of Ig. One of 3 IgA myeloma proteins tested, TEPC 15, bound to staphylococci. The Fc specificity of this interaction was confirmed by chromatography on protein A-Sepharose and by inhibition studies using polyclonal human IgG. The protein A reactivity of this monoclonal protein was detected in IgA aggregates and absent in the monomeric form of IgA.