Rheumatoid factors in mice: plaque assay for homophile and heterophile rheumatoid factors.

It was found that a high proportion of IgM-producing cells secrete homophile or heterophile rheumatoid factors (RF). Injection of lipopolysaccharide (LPS) into CBA mice resulted in a sharp increase in total IgM and in RF-producing cells and in some cases resulted in an increase in RF-producing cells as a proportion of total IgM. RF plaques are indirect IgM in the sense that they require development by IgG2 (anti-IgM) antibody for visualization in a standard haemolytic plaque assay. The RF response to LPS is both dose- and time-dependent.