Activated CD27+ and CD27- memory B cells accumulate in the joints of patients with juvenile idiopathic arthritis

The expression of the costimulatory molecules CD80 and CD86 was increased on synovial fluid CD19+ B cells as compared to peripheral blood. CD80/CD86 expression on these B cells could be shown to induce alloreactive T cell proliferation in vitro. Most of the synovial fluid B cells belonged to the CD27+IgDclass-switched memory B cell subset. However, almost half of the CD27 negative synovial B cells ("naïve" B cells lacking the memory B cell marker CD27) showed molecular characteristics of memory B cells (isotype switching, somatic hypermuation). These B cells also expressed increased levels of CD80/ CD86 as compared to CD27-IgD+ naïve B cells of the synovial fluid.