4C, D). However, not only γδCD8αα+ iIEL but also αβCD8α+ iIEL cells showed a basal [Ca2+]i decrease. This was unlikely to be a direct effect of the GL3 mAb on αβ iIEL but may be due to changes in the composition of αβCD8α+ iIEL, e.g. through attraction of systemic αβ+CD8+ cells with lower basal [Ca2+]i levels into the gut epithelium 40. In contrast, basal [Ca2+]i levels of neither systemic CD8− p-γδ nor CD8− i-γδ were altered by GL3-treatment (Fig. 4C and D). These data suggest that the observed high basal [Ca2+]i levels of γδCD8αα+ Navitoclax nmr iIEL reflect a constant TCR-specific activation in vivo,

which could be partially blocked by anti-γδ TCR mAb treatment. Next, we investigated how γδ T cells from GL3-treated γδ reporter mice responded to TCR stimulation. As shown in Fig. 4A, the TCR complex was down-regulated

but still present at residual levels on the cell surface of these γδ T cells. We found that anti-CD3 and anti-γδ PD-0332991 chemical structure TCR mAb clustering still elicited Ca2+-fluxes in CD8− p-γδ and CD8− i-γδ from mice injected with GL3, albeit with lower or almost flat amplitudes compared with those from mock-treated animals. The iIEL populations CD8+ i-γδ and CD8+ i-αβ only showed a decrease of basal [Ca2+]i, without evident mAb-induced Ca2+-flux neither in PBS nor in GL3 treated mice (Fig. 5A). The quantification of these changes, displayed as fold of basal [Ca2+]i Cyclin-dependent kinase 3 levels after anti-CD3 and anti-γδ TCR mAb clustering, showed that CD8− p-γδ and CD8− i-γδ were affected by the GL3 treatment (Fig. 5B). In addition, iIEL from PBS- and GL3-treated γδ reporter mice were analyzed

for responsiveness to ex vivo stimulation with GL3 and GL4, a different anti-γδ TCR mAb. In vivo treatment with GL3 reduced the TCR-dependent CCL4 and IFN-γ production of γδ iIEL (Fig. 5C). Surprisingly, the CCL4 and IFN-γ production capability of γβ iIEL from GL3-treated γδ reporter mice stimulated ex vivo with the anti-αβ TCR (H57) was increased (Fig. 5D). In conclusion, γδ iIEL suffered a loss of function in response to TCR stimuli when their TCR was modulated by GL3 treatment for 6 days. Together, this suggests that the iIEL do not become exhausted and do not change their activated phenotype with repeated high-dose anti-γδ TCR treatment. However, the down-modulation of their surface TCR in combination with the decoration of residual surface γδ TCR is likely to be the reason for the diminished TCR responsiveness and cytokine production. This further implies a role for the TCR in the physiology of γδ T cells. However, it is at present not clear to what extent the responsiveness of γδ T cells to other stimuli, e.g. engagement of other receptors such as NKG2D or TLR, may be also altered by TCR modulation. The question whether, after thymic selection, the TCR on γδ T cells had a physiological role at all was not unanticipated 19, 23.