Mononuclear phagocytes in rheumatoid arthritis: Fc-receptor expression by peripheral blood monocytes

Fc receptor expression by enriched monocytes from rheumatoid arthritis (RA) patients and age and sex matched controls (healthy subjects) was compared by measuring the uptake of IgG on monocytes in a competitive radioassay. The association constant (Ka) between IgG and the monocytes and the number of Fc binding sites per cell was calculated from Scatchard plots of 4 degrees C binding data. RA monocytes had increased expression of Fc receptors as compared with those of controls. This increase was particularly pronounced in those RA patients affected by extra-articular disease. There were significant correlations between the numbers of Fc receptors on monocytes and both C1q binding and anticomplementary activity but none between monocyte Fc receptor numbers and serum rheumatoid factors (IgG and IgM). It is considered that monocyte handling of circulating immune complexes is unimpaired in RA and that monocytes make an adaptive response to increased levels of immune complexes.