Demonstration of separate receptors for human IgA and IgG in group A streptococci type 4. Separation of the solubilized receptors from group- and type-specific antigens, lipoteichoic acid and peptidoglycan.

The alkaline extract of group A streptococci type 4 was separated by electrophoresis and diffused against 27 normal human sera. One of the precipitates appeared with 85% of the sear. Addition of purified IgA myeloma protein or sera containing IgA M-components to the extract changed the electrophoretic mobility of the precipitate anodically. Purified IgG Fc-fragments or sera containing IgG M-component did not affect the mobility of the precipitate. It was concluded that this precipitate contained the streptococcal receptor for human IgA. A non-precipitating IgG Fc-receptor, with agglutinating capacity for cells coated with human IgG1 but not IgG3, was localized by preparative electrophoresis to the same electrophoretic region as the IgA receptor. The mobility of the IgG receptor remained unaltered on addition of IgA myeloma protein permitting a separation of the two receptors by preparative electrophoresis. The receptors were distinct from the group specific carbohydrate, peptidoglycan and lipoteicholic acid. No M antigen or opacity factor were demonstrated in the extract.