Restricted heterogeneity of polyclonal rheumatoid factors.

The electrophoretic pattern of rheumatoid factor (RF) was investigated in 40 polyclonal sera, by using radiolabeled IgG. Thirty sera specifically bound IgG aggregates, correlating with their RF titer. The binding pattern was monoclonal or oligoclonal. The molecules responsible were classic RF antibodies, as shown by using purified IgM, inhibition experiments, and by the optimal size of aggregates (2,000-4,000 kd). These data show that RF heterogeneity is restricted in polyclonal sera, and this can have a bearing on several mechanisms.