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The group A streptococcal receptor for human IgA binds IgA via the Fc-fragment
Eight freshly isolated type M4 strains of group A streptococci were found to bind between 60 and 80% and 2.5 microgram radiolabelled IgA myeloma protein in a standard test system, while a reference type 4 strain bound only 20%. Commercial human IgG or IgG1 myeloma protein did not inhibit the binding of IgA by the reference type 4 strain or one of the freshly isolated type 4 strains, whereas inhibition was obtained by purified polyclonal IgA myeloma protein. Fc fragments of purified IgA1 myeloma protein, obtained by digestion with gonococcal protease, inhibited binding or radiolabelled IgA1, while the Fab fragments had no inhibitory effect.
Eight freshly isolated type M4 strains of group A streptococci were found to bind between 60 and 80% and 2.5 microgram radiolabelled IgA myeloma protein in a standard test system, while a reference type 4 strain bound only 20%. Commercial human IgG or IgG1 myeloma protein did not inhibit the binding of IgA by the reference type 4 strain or one of the freshly isolated type 4 strains, whereas inhibition was obtained by purified polyclonal IgA myeloma protein. Fc fragments of purified IgA1 myeloma protein, obtained by digestion with gonococcal protease, inhibited binding or radiolabelled IgA1, while the Fab fragments had no inhibitory effect.