B-lymphocyte subpopulation which forms rosettes with mouse erythrocytes increased in rheumatoid arthritis.

We studied the peripheral blood lymphocytes of 22 patients with rheumatoid arthritis (RA) for the presence of a subpopulation of cells which form rosettes with mouse erythrocytes. In normal subjects these cells have been characterised as immature B cells which are non-responsive to pokeweed mitogen. The mean percentage of mouse rosette-forming cells (MRFC) in the rheumatoid group was 13 +/- 10(mean +/- 2 SD), a significantly higher value than the control mean of 5% +/- 4% (P less than 0.001). The T- and B-cell percentages in the rheumatoid patients were normal. The ratio of MRFC: B cells derived from these results was 3:4 in RA and 1:4 in normal subjects. Pre-incubation of rheumatoid peripheral blood lymphocytes at 4 degrees C gave higher values of MRFC (19% +/- 10%) than pre-incubation at 37 degrees C (13% +/- 10%, P less than 0.02), but no such temperature effect was found in the control group. There was no correlation between MRFC and rheumatoid disease activity or the patients' drug regimens. We conclude that the threefold increase in mean MRFC in patients with rheumatoid arthritis indicates an abnormality in the circulating B-cell pool.