Mycobacteria-induced Gr-1+ subsets from distinct myeloid lineages have opposite effects on T cell expansion

Similar to the regulation of vasodilation, the balance between NO and superoxide (O-2(-)) regulates expansion of activated T cells in mice. Reduction of suppressive NO levels by O-2(-) is essential for T cell expansion and development of autoimmunity. In mice primed with heat-killed Mycobacterium, a splenocyte population positive for Gr-1 (Ly-6G/C) is the exclusive source of both immunoregulatory free radicals. Distinct Gr-1(+) cell subpopulations were separated according to Ly-6G expression. In culture with activated T cells, predominantly monocytic Ly-6G(-) Gr-1(+) cells produced T cell-inhibitory NO but no O-2(-). However, mostly granulocytic Ly-6G(+) cells produced O-2(-) simultaneously but hail no measurable effect on proliferation. Recombination of the two purified Gr-1(+) subpopulations restored controlled regulation of T cell proliferation through NO and O-2(-) interaction. Coculture of p47(phox-/-) and inducible NO synthase(-/-) Gr-1(+) cells confirmed this intercellular interaction. These data suggest that bacterial products induce development of distinct Gr-1(+) myeloid lineages, which upon stimulation by activated T cells, interact via their respective free radical products to modulate T cell expansion.