Notch Ligand Delta-like 4 Promotes Regulatory T Cell Identity in Pulmonary Viral Infection.

Regulatory T (Treg) cells establish tolerance, prevent inflammation at mucosal surfaces, and regulate immunopathology during infectious responses. Recent studies have shown that Delta-like ligand 4 (Dll4) was upregulated on APC after respiratory syncytial virus (RSV) infection, and its inhibition leads to exaggerated immunopathology. In the present study, we outline the role of Dll4 in Treg cell differentiation, stability, and function in RSV infection. We found that Dll4 was expressed on CD11b+ pulmonary dendritic cells in the lung and draining lymph nodes in wild-type BALB/c mice after RSV infection. Dll4 neutralization exacerbated RSV-induced disease pathology, mucus production, group 2 innate lymphoid cell infiltration, IL-5 and IL-13 production, as well as IL-17A+ CD4 T cells. Dll4 inhibition decreased the abundance of CD62LhiCD44loFoxp3+ central Treg cells in draining lymph nodes. The RSV-induced disease was accompanied by an increase in Th17-like effector phenotype in Foxp3+ Treg cells and a decrease in granzyme B expression after Dll4 blockade. Finally, Dll4-exposed induced Treg cells maintained the CD62LhiCD44lo central Treg cell phenotype, had increased Foxp3 expression, became more suppressive, and were resistant to Th17 skewing in vitro. These results suggest that Dll4 activation during differentiation sustained Treg cell phenotype and function to control RSV infection.