Precipitation of streptococcal peptidoglycan by human sera: influence of anti-immunoglobulins.

Antibodies to streptococcal peptidoglycan (PG) were detected by gel-precipitation in 38% of sera from blood donors and in 71% of sera with a Waaler-Rose test titre of greater than or equal to 1:64. Twenty-six rheumatoid arthritis sera revealed patterns of interference with complete or partial fusion between PG and aggregated human IgG while none of the sera precipitating both these preparations showed non-interference. The reactions were interpreted as denoting interference between the PG-antibody complexes and aggregated IgG. Conversion of some non-precipitating blood donor sera to PG precipitation was obtained by addition of isolated rheumatoid factor, in itself not precipitating PG, to the sera. Thus, the high frequency of PG precipitation among rheumatoid arthritis sera could--at least in part--be attributed to the participation of anti-IgG in the reaction.