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.