Preferential reactivity of certain human and rabbit IgM and IgG rheumatoid factors with mildly reduced and amidomethylated IgG.

Two broadly defined populations were identified in affinity column-enriched rabbit and human rheumatoid factor (RF) preparations: one population reacted preferentially with mildly reduced and alkylated (MRA) homologous (with regard to species) IgG, and the other reacted preferentially with native, intact IgG. Each of these reactivities was identified by preferential association of RF with either intact or MRA IgG-Sepharose 4B conjugates and existed in both the IgM and IgG immunoglobulin classes. Use of soluble IgG inhibitor preparations in RF- dependent hemolytic and hemagglutination inhibition in RF-dependent hemolytic and hemagglutination inhibition assays showed that the preferred form of IgG inhibitor paralleled the preference of a particular RF preparation for a particular IgG affinity matrix. In addition, preferential reactivity was observed toward either intact or MRA Fc gamma inhibitors. On a molar basis RF reactivity with Fc gamma was significantly less than that observed in the presence of whole IgG. In contrast, neither IgG Fab nor F(ab')2 fragments were reactive with either of the 2 specificity populations of RF. The distribution of immunoglobulin class relative to specificity suggested that preferential reactivity with MRA IgG was usually associated with IgM RF, and reactivity with intact IgG was usually associated with IgG RF. These data suggest that in vivo perturbation of IgG structure may lead to an RF response identifiable by reactivity with an altered monomeric form of IgG.