Distinct IgG1 and IgG3 subclass responses to two streptococcal protein antigens in man: analysis of antibodies to streptolysin O and M protein using standardized subclass-specific enzyme-linked immunosorbent assays.

The IgG subclass composition of antibodies to two streptococcal protein antigens in sera following infection was analysed by enzyme-linked immunosorbent assays (ELISA). The assays were standardized using 5-iodo-4-hydroxy-nitrophenacetyl (NIP)-specific chimeric antibodies, to permit quantitative comparisons between subclasses. Antibodies to streptolysin O (SLO) were predominantly IgG1, with only minor contributions from the other subclasses. In contrast, antibodies to M protein were distributed between the IgG1 and IgG3 subclasses, and in approximately half the sera IgG3 predominated. The ratio of IgG1:IgG3 was greater for SLO than for M protein in 22/23 sera. Little or no IgG4 antibody was detected to either antigen. Functional affinities of the IgG1 and IgG3 antibodies, determined by inhibition ELISA, were comparable for the two antigens. The demonstration that two protein antigens encountered during streptococcal infection elicit antibody responses with markedly different subclass profiles has implications for IgG subclass regulation and vaccine development.