However, OVA-pulsed viable DC that had taken up apopotic DC failed to induce OVA-specific T-cell proliferation HSP inhibitor (Fig. 5F). These results indicate that upon uptake of apoptotic DC but not necrotic DC, viable DC are refractory to LPS-induced maturation. As viable DC acquired a tolerogenic phenotype upon apoptotic DC uptake, we then assessed the ability of viable DC to induce Treg differentiation upon apoptotic DC uptake. Culture of naïve CD4+CD25– OT-II T cells with OVA-pulsed viable DC resulted in approximately 4–5% of naïve T

cells differentiating into Foxp3+ Treg, which increased to approximately 23–24% upon culture with OVA-pulsed MG-132 solubility dmso viable DC that had taken up apoptotic DC. In contrast, culture of naïve CD4+CD25– T cells with OVA-pulsed viable DC that had taken up necrotic DC only resulted in approximately 5–6% Foxp3+ Treg (Fig. 6A and B). The increase in the proportion of Foxp3+ Treg was not paralleled by an increase in the absolute T-cell count, indicating that it was likely the induced expression of Foxp3 and not expansion, which mediated the observed increase in the proportion of Foxp3+ Treg among T cells cultured with OVA-pulsed viable DC that had taken up apoptotic DC (data not shown). In order to test whether the induction of Foxp3+ Treg

was induced specifically upon uptake of apoptotic DC by viable immature DC and not by uptake of other types of apoptotic cells, we looked at the effects of apoptotic splenocyte uptake on the ability of viable

DC to induce Foxp3+ Treg. Results indicate that the uptake of apoptotic splenocytes did not enhance the ability of viable DC to induce Treg, as only 7–8% of naïve T cells differentiated into Foxp3+ Treg, which was similar to the control group. Furthermore, we also assessed the ability of in vitro-generated Foxp3+ Treg to suppress T-cell proliferation. Bcl-w Our findings identify that the CD4+CD25+ T-cell subset only from the co-culture of naïve T cells and OVA-pulsed viable DC that had taken up apoptotic DC, was in fact enriched for suppressor T cells, as they were able to inhibit T-cell proliferation in a dose-dependent manner (Fig. 6C). Overall, these results indicate that it was specifically the uptake of apoptotic DC which was primarily responsible for the induction of Foxp3+ Treg by viable DC. Next, we wanted to assess whether the ability to induce Foxp3+ Treg by viable DC upon apoptotic DC uptake dependent on interaction with naïve T cells or soluble factors. This was tested by separating T cells from DC using a transwell plate followed by an assessment of Foxp3+ Treg induction.