Comparative analysis of CD45RA- and CD45RO-positive CD4⁺T cells in peripheral blood, synovial fluid, and synovial tissue in patients with rheumatoid arthritis and osteoarthritis

 To determine whether the predominant infiltration with memory CD4⁺T cells in joints is specific to the local immune and inflammatory response in rheumatoid arthritis (RA), the proportions of CD45RA⁺ or CD45RO⁺ cells in the CD4⁺T cell populations in three different compartments (i.e., peripheral blood, synovial fluid, and synovial tissue) from patients with RA and osteoarthritis (OA) were compared by two-color flow-cytometric analysis. In the CD4⁺T cell population of peripheral blood, the number of CD45RO⁺ cells was relatively higher than CD45RA⁺ cells in both RA and OA patients, but their percentages did not differ from those found in healthy individuals. However, the great majority of CD4⁺T cells present in synovial fluid and synovial tissue were CD45RO-positive and CD45RA-negative in both patient groups; although CD4⁺T cells infiltrating both the disease compartments were markedly greater in RA joints, their mean percentages of CD45RO⁺ cells were not significantly different from those in OA joints. These data indicate that an accumulation of CD45RO⁺ memory CD4+T cells is a generalized phenomenon during local inflammatory responses in both RA and OA joints, and may be due mainly to the propensity of these cells to preferentially transmigrate into the inflamed joint via adhesion molecules as compared with CD45RA⁺ naive CD4⁺T cells.