We therefore addressed whether PBP2 could promote the immunogenic properties of DCs. To study this issue, we first performed in vitro allogeneic mixed lymphocyte reactions (MLR). Indeed, the allostimulatory capacity of DCs could be analysed by comparing the proliferation of allogenic T cells upon culture with untreated or PBP2-treated DCs. We studied T cell proliferation by analyzing the dilution of the PD-0325901 fluorogenic probe DDAO-SE (Figure 2B left panel). We observed that the percentage of proliferating allogeneic T cells was increased when stimulatory DCs have been previously treated with PBP2 as compared to untreated cells. PBP2-treated DCs showed similar capacity to stimulate allogeneic T cells as compared to LPS-treated DCs (data not shown). PBP2-treated human monocyte-derived DCs also increased its allostimulatory capacities as shown by 3H-thymidine uptake experiments (Figure 2B right panel). PBP2 treatment of purified T cells (not co-cultured with DCs) did not induce their proliferation (data not shown). To investigate whether PBP2 treatment promotes immunogenic DC properties in vivo, we used a HDAC inhibitor transgenic mouse model in which autoimmune diabetes is induced by mDCs. Ins- HA transgenic mice adoptively transferred with naive anti-HA CD8+ T cells developed diabetes in 6-9 days, only when immunized with both matured and HA peptide-loaded DCs and not when DCs were either immature or not loaded with HA peptide (Figure 2D). Importantly, PBP2-treated DC triggered diabetes as effectively as LPS-matured DCs. Altogether, these results show that in vitro treatment of mouse DCs with PBP2 increases its immunostimulatory properties in vitro and in vivo. We then explored the ability of PBP2 to work as an immunological adjuvant for anti-meningococcal immune responses. We immunized BALB/c mice subcutaneously with one dose of purified PBP2 (3 mg), or alternatively, with one dose of purified capsular polysaccharide X (20 mg) or both. Mice were sacrificed 10 days later and immune response, IgG production, was determined in blood against both PBP2 and purified capsular polysaccharide of serogroup X by ELISA.