Protein B: a versatile bacterial Fc-binding protein selective for human IgA.

Protein B, a selective bacterial IgA Fc-binding protein isolated from group B streptococci, has been used to quantify fluid phase and immobilized human IgA. Protein B detects both human IgA1 and IgA2 subclasses and is also reactive with secretory IgA. Protein B can be used immobilized to microtiter plates to capture IgA or following biotinylation as a tracer for fluid phase or immobilized human IgA. The studies presented here suggest protein B will prove to be a valuable reagent for quantitative immunochemical procedures involving human IgA antibodies and facilitate a variety of studies of IgA responses in man.