The CD19+ CD25+ population was enriched in PB and in the inflamed synovial fluid compared with BM (Fig. 4a). Mononuclear cells in PB sorted into CD19+ CD25+ and CD19+ CD25− subsets were stimulated with EBV (3·6 × 106 copies/ culture). The CD25+ cultures responded to EBV stimulation with a significant increase in the number of immunoglobulin-producing cells, but no increase was observed in CD25– cultures of

the same RA patient (Fig. 4b). The stimulatory effect was seen on the IgM- and IgG-producing CD25+ cells. Similar EBV stimulation of the CD25+ cultures from healthy subjects had no increase of immunoglobulin-producing cells (Fig. 4c). We have previously shown that RA patients with EBV replication in BM present a better clinical response to RTX treatment.[25] Interestingly, RTX treatment was associated with a clear reduction of EBV load in patients with RA. These CB-839 mw data allowed us to speculate that active EBV might be harboured within the RTX-sensitive B-cell populations in vivo. As a consequence, in the present study we assessed the impact of EBV infection on the phenotype and function of B cells in blood and BM of patients with RA. The present study identifies the CD25+ subset of B cells to be enriched in PB of EBV+ RA patients suggesting that this CAL-101 solubility dmso population might be an important source of EBV infection for reactivation and re-infection of the RA patient.

Importantly, EBV transfection has shown an induced CD25 expression in Hodgkin’s lymphoma cells and in Burkitt’s lymphoma cells[51, 53] and in natural killer cell lines.[52] Similarly,

EBV-specific T cells can be selected using CD25.[54] In patients with RA, the CD25+ B-cell subset belongs to the memory pool of B cells, which is functionally characterized by an increased IL-10 secretion and low spontaneous immunoglobulin secretion.[43-45] We found that the CD25+ B-cell population was enriched with the cells Urocanase expressing the activation and apoptosis marker CD95. This is supported by our previous data where we observed that EBV replication gave rise to a concomitant expression of CD95 on CD19+ B cells and this might increase the sensitivity to RTX-induced depletion.[25] On the other hand, it has been shown that cells from patients with RA may be resistant to CD95-mediated apoptosis.[55] In EBV+ RA patients an increased frequency of CD25+ CD27+ memory cells are found. CD27 is shown to be critical for several steps of EBV infection, and CD27+ B cells are considered as a reservoir of EBV in the viral latency phases.[56, 57] CD27 expression has recently been identified as essential for combating EBV infection, because individuals with CD27 deficiency develop combined immunodeficiency, hypogammaglobulinaemia and persistent symptomatic EBV viraemia.[58, 59] Interestingly, it has been shown that B cells in the rheumatic synovia express latent membrane proteins 1 and 2A, the EBV-encoded proteins that provide additional survival and maturation signals to B cells.