1A), in line with previously published results [20]. Activation of Vav1AA/AA T cells as measured by surface expression of CD25 was also impaired compared to WT T cells, although they reached almost WT levels of surface CD25 under strong stimulatory conditions. In addition, IL-2 secretion was severely reduced in Vav1AA/AA T cells, which might contribute to the impaired proliferative potential (Fig. 1B). As T cell proliferation

and activation by antibody-mediated stimulation is affected by the loss of Vav1 GEF activity, we wanted to know if Vav1 GEF activity also affects allogeneic T cell proliferation. To address this question, we cultured equal numbers of purified T cells of Vav1AA/AA mice or WT control animals with irradiated splenocytes from fully mismatched allogeneic BALB/c mice in a one-way mixed lymphocyte reaction (MLR). Whereas WT T cells proliferated strongly

in response selleck products to increasing numbers of stimulator cells, Vav1AA/AA T cells showed a marked impairment of proliferation in response to allogeneic stimulation (Fig. 2A). To compare this phenotype to total Vav1 deficiency, we used T cells from Vav1−/− mice in the MLR. T cells from Vav1−/− mice also showed a strong proliferative 17-AAG defect as observed before (Fig. 2B) [23], which, despite the total Vav1 deficiency, is only slightly stronger compared to Vav1AA/AA T cell. These results indicate that the GEF function of Vav1 has a key role in the proliferation and activation of allogeneic T cells.

To test whether the observed proliferation defect of Vav1AA/AA T cells in vitro translates into an in vivo situation, we used splenocytes from Vav1AA/AA or WT mice in a systemic graft-versus-host (GvH) model. CFSE-labeled splenocytes from Vav1AA/AA or control mice were injected into BALB/c SCID mice, and alloantigen-driven proliferation of donor T cells in the recipient spleen was measured Tangeritin after 4 days. To account for the reduced number of single-positive T cells in Vav1AA/AA mice which is caused by a developmental defect in the thymus [20], the number of injected splenocytes was increased accordingly to achieve equal number of injected T cells for the Vav1AA/AA and WT groups. In addition, a third group treated with cyclosporine A (CsA) was included as a control for strong immunosuppression. In mice treated with CsA, the number of total splenocytes as well as CD4+ and CD8+ T cells in the spleen was reduced after 4 days compared to control mice. Interestingly, an almost equally pronounced reduction in splenocytes and T cells from Vav1AA/AA mice was observed (Fig. 3A). To examine the proliferation of allogeneic T cells in more detail, the number of cell divisions was analyzed for CD4+ and CD8+ T cells by CFSE dilution.