NOS2 and atrial fibrillation: As shown in Figure 6C, AF-induced CD14+HLA-DR–/low MDSC suppressed the proliferation of autologous CD4+ and CD8+ T cells as described above, however, addition of either nor-NOHA or SMT into T cell/MDSC cocultures rescued T-cell proliferation with concomitant inclusion of nor-NOHA and SMT almost completely abrogating the immunosuppressive effect of those MDSC, pointing to the critical role of both ARG1 and iNOS in mediating the immunosuppressive activity of AF-induced CD14+HLA-DR–/low MDSC.