Hidden Rheumatoid Factors Reacting with “Non a” and other Antigens of Native Autologous IgG

Abstract

Several rheumatoid factor activities were revealed in 14 rheumatoid sera after the separation of IgM rheumatoid factors from inhibiting autologous IgG by gel filtration. These included a “new” specificity, anti-“non a.” Anti-Ga, found in 14 sera, anti-Gm(a), found in 10, and anti-“non a,” found in 6, were the most frequently detected rheumatoid factor specificities, while anti-Gm(g) was found in one serum. The anti-“non a” and anti-Ga rheumatoid factors reacted with antigens present in native autologous IgG. The original anti-Gm(p) and anti-Gm(e) rheumatoid sera contained anti-“non a” together with anti-Ga, and the respective original anti-Rh antibodies carried both the “non a” and Ga antigens. Gm(p) and Gm(e) appeared to be identical in part with “non a” and in part with Ga, and thus were not regular Gm types. The antigen for rheumatoid anti-“non a” was found to be located on the pFc' fragment of IgG. In contrast, the antigen for anti-Ga was present on Fc, but not on the pFc' fragment. Thus two distinct molecular regions of Fc were involved in the rheumatoid factor reactions.