Relative reactivities of rheumatoid factors in serum and cells. Evidence for a selective deficiency in serum rheumatoid factor.

Investigations of rheumatoid factors by a hemolytic plaque forming cell assay of blood lymphocytes with sensitized sheep cells have suggested that the rheumatoid factors released from the cells have higher affinities for human IgG than do the rheumatoid factors measured in the patient's serum. This study reaffirms this observation and provides evidence that the reported differences are not artifacts of technique. The findings imply that rheumatoid factors of higher affinity for IgG than those of the serum are being released into the tissue fluids by lymphocytes and locally precipitated. Such rheumatoid factors may never reach the peripheral blood serum in detectable quantity or may do so only infrequently.