Regulation of antibody responses by rheumatoid factor. I. Polyclonal activation of human B cells by rheumatoid factor-containing preparations from seropositive plasma.

Rheumatoid factor (RF)-containing IgM preparations isolated from the plasma of two seropositive patients were able to increase the number of Ig-secreting cells in normal human peripheral blood lymphocyte cultures. This polyclonal B cell activation was optimal in the presence of both T cells and monocytes. A relationship was established between the activator and RF in these preparations based on the ability of both to bind to insolubilized human IgG. The presence of the activator also coincided with the presence of large, RF-containing Ig complexes. These data suggest that RF contributes to the formation of B cell-stimulating immune complexes--a phenomenon with possible negative consequences in disease states characterized by these complexes.