Binding of human IgA to HCl-extracted c protein from group B streptococci (GBS).

The c beta protein of group B streptococci obtained by HCl extraction appears as a ladder-like pattern in SDS-PAGE when detected by a rabbit anti-c beta serum, and a similar picture is seen when the crude extract is incubated with human IgA and an anti-human IgA conjugate. Affinity-purified c beta antigen and IgA receptors from GBS gave identical pictures in Western blots using rabbit anti-c beta serum. Both the c beta antigen and the IgA receptor are exposed on the surface of GBS as demonstrated by immunofluorescence.