Demonstration of the non-identity between the Fc receptor for human IgG from group A streptococci type 15 and M protein, peptidoglycan and the group specific carbohydrate.

After electrophoresis of an alkaline extract of type 15 group A streptococci, three main precipitation lines were obtained in diffusion experiments against commercial human polyclonal IgG (lines 1, 2 and 3). Nineteen of 23 sera (83%) from apparently healthy human individuals gave line 3, while 6 of them (26%) gave line 1. The sera giving line 1 did also give line 3. Line 2 was obtained with 2 sera only, also giving lines 1 and 3. Line 3 was caused by a streptococcal Fc-receptor for human IgG, since the line could be displaced by addition of Fc-fragments, but not Fab-fragments of pooled human IgG. Line 1 was shown to be different from line 3, since (1) line 1 was suppressed in contrast to line 3 on absorption of a human serum or commercial polyclonal human IgG with S. aureus; and (2), line 1 was suppressed by Fab-fragments but not Fc-fragments of polyclonal human IgG. Line 2 could be inhibited by addition of peptidoglycan to commercial polyclonal human IgG or a human serum investigated. Another line, 4, obtained in diffusion experiments involving electrophoretically separated alkaline extract of type 15 group A streptococci was type-specific as shown by rabbit antisera to streptococci type M1, M8, M15, and T44, and disappeared on trypsinization of the extract. The component responsible for line 4 in the streptococcal extract, judged to be type-specific M protein, had a mobility different from the component responsible for line 3 in electrophoresis.