NOS2 and viral infectious disease: MuLV/Friend virus infection increased the accumulation of both G-MDSCs and monocytic myeloid-derived suppressor cells (M-MDSCs) in both WT and Sash mice, but only elevated the expression of PD-L1 and iNOS on G-MDSCs in WT mice, but not in Sash mice (Figures 2C, D).