Abstract: Objective To explore the role of DNAM-1 in the activation, proliferation and function of type I regulatory T cells (Tr1 cells). Methods Anti-CD3/CD28 antibodies were used to stimulate mouse T cells derived from the spleen of wild- type (WT) mice, and the expression level of DNAM-1 in resting and activated Tr1 cells was evaluated with flow cytometry. Na?ve CD4+T cells isolated by magnetic cell sorting from the spleens of WT mice and DNAM-1 knockout (KO) mice were cultured in Tr1 polarizing conditions for 3 days, after which CD25 and CD69 expressions were measured using flow cytometry. The induced Tr1 cells were labelled with CFSE and cultured in the presence of anti-CD/CD28 antibodies for 3 days, and their proliferative activity was analyzed. The expressions of IL-10 and p-STAT5 in DNAM-1-deficient Tr1 cells were detected before and after IL-2 stimulation. Results The expression level of DNAM-1 was significantly upregulated in CD4 + T cells and Tr1 cells after stimulation with anti-CD3/CD28 antibodies (P<0.05). DNAM-1 knockout did not cause significant changes in the number or proportion of Tr1 cells, but but significantly increased the expression levels of the activation markers CD69 and CD25 (P<0.05). Compared with WT Tr1 cells, DNAM-1-deficient Tr1 cells exhibited reduced proliferative activity in vitro (P<0.05) with downregulated IL-10 production (P<0.05) and decreased expressions of Il-10 and Gzmb mRNA (P<0.05). In DNAM-1-deficient Tr1 cells, IL-2 stimulation significantly reduced IL-10 secretion level and the expression of p-STAT5 as compared with WT Tr1 cells. Conclusion DNAM-1 participate in the activation and proliferation of Tr1 cells and affect the biological functions of Tr1 cells through the IL-2/STAT5 pathway.

Key words: DNAM-1; type I regulatory T cells; interleukin-2; STAT5; interleukin-10