We found that

IL-2, IL-4 and IFN-γ levels were extremely low in both DPP2 kd and control mice (data not shown). This is most likely due to the low percentage of OVA-specific T cells responding to antigen restimulation in vitro. In contrast, the level of IL-17 was significantly increased in DPP2 kd lymphocytes (Fig. 6B). Thus, in the absence of DPP2, the in vivo immunization led to the generation of Th17 memory cells, although the adjuvants CFA and IFA had presumably induced the full set of exogenous cytokines, necessary for Th1 and Th2 differentiation in vivo. Consistent with the higher level of IL-17 production, DPP2 kd T cells also upregulated Buparlisib order il-17a (Fig. 6C) and rorγt (Fig. 6D) transcript levels. Th17 cells are potent inducers of autoimmunity. Since activation of T cells from lck-DPP kd mice leads to differentiate into Th17 cells, these mice were examined for signs of autoimmunity. Interestingly, we observed that the level of circulating anti-nuclear

HTS assay antibodies (ANA) was increased in 6-month-old lck-DPP2 kd compared with control littermates (Fig. 7). ANA were detected on HEp-2 cells at serum dilutions of 1:50 and 1:100, but not 1:300, indicating that DPP2 kd mice have relatively low titers of circulating autoantibodies. The localization of the ANA to the nucleoli of the HEp-2 cells suggests the presence of anti-RNA, rather than anti-DNA, autoantibodies. Total Ig and IgM serum levels were quantified by ELISA, but no differences were observed between DPP2 kd and control mice (Supporting Information Fig. 3). Furthermore, pathological studies performed on these mice revealed no inflammation, lesions or cellular infiltrates. It is possibly, therefore, that the full development of autoimmunity takes 12–15 months. Our data indicate very that

DPP2 is a quiescence factor that is required for the maintenance of T cells in G0 in vivo. In the presence of this dipeptidase, T-cell differentiation into effector cells depends on TCR signals, as well as exogenous factors. In lck-DPP2 kd mice, however, the threshold of TCR-mediated activation is lowered, resulting in increased proliferation and differentiation into IL-17 secreting cells, independently of exogenous cytokines. Thus, IL-17 production seems to be the default pathway for T-cell differentiation, a process that is actively prevented by DPP2, providing a new model for the control of T-cell activation and differentiation. In our previous work we observed that in vitro inhibition of DPP2 enzyme activity or downregulation of its expression in quiescent T cells and fibroblasts leads to deregulated entry into the cell cycle, resulting in apoptosis of these cells 3–5. To further elucidate the function of DPP2, development of an in vivo model was essential.