CD5 positive B cells in patients with rheumatoid arthritis: phorbol ester mediated enhancement of detection.

CD5 molecules present on human T cells are detectable but weakly expressed on some human B cells. We have increased the sensitivity of their detection by treating the B enriched cells with phorbol myristic acetate (PMA), a tumour promoting agent. The numbers of CD5+ B cells in the blood of patients with rheumatoid arthritis (RA) were higher than in control blood, and after PMA treatment this was statistically significant. CD5+ B cells were also increased in tonsils, lymph nodes, and spleens after PMA activation. There were no significant differences between the percentages of B cells carrying chi or lambda light chains in their expression of CD5 molecules in patients with RA.