Objective. To analyze subsets of primed T helper cells, defined by expression of the CD45RB isoform of the leukocyte common antigen, in the blood and synovial fluid (SF) of patients with rheumatoid arthritis (RA).
Methods. Three-color immunofluorescence was used to study CD45 isoform expression by peripheral blood and SF CD4+ T cells.
Results. CD45 isoform expression in the peripheral blood of patients with either RA or reactive arthritis did not differ from that in healthy controls. SF T cells from both RA patients and reactive arthritis patients were almost exclusively primed (CD45RO+) cells. RA SF T cells expressed very low levels of CD45RB; this is the most highly differentiated subset of primed cells. Patients with acute reactive arthritis showed higher levels of CD45RBbright cells in their synovial fluid.
Conclusion. The highly selected cell population in SF, representing one subset of primed cells, may relate to the apparent functional abnormalities of cells from this site in patients with RA.