Superoxide prevents nitric oxide-mediated suppression of helper T lymphocytes: Decreased autoimmune encephalomyelitis in nicotinamide adenine dinucleotide phosphate oxidase knockout mice

NO, which suppresses T cell proliferation, may be inactivated by superoxide (O-2(-)) due to their strong mutual affinity. To examine this possibility, preactivated Th clones were cocultured with stimulated macrophages. PMA neutralized the inhibitory activity of NO, which aas dependent on extracellular O-2(-) production. In contrast, macrophages from p47(phox -/-) (pKO) mice, which lack functional NADPH oxidase, retained their NO-dependent inhibition of T cell proliferation upon stimulation with PMA, indicating that NADPH oxidase is the major source of NO-inactivating O-2(-) in this system. To examine the NO-O-2(-) interaction in vivo, the role of NADPH oxidase in experimental autoimmune encephalomyelitis was studied in pKO mice. No clinical or histological signs were observed in the pKO mice. Neither a bias in Th subsets nor a reduced intensity of T cell responses could account for the disease resistance. Although spleen cells from pKO mice proliferated poorly in response to the immunogen, inhibition of NO synthase uncovered a normal proliferative response, These results indicate that NO activity may play a critical role in T cell responses in pKO mite and that in normal spleens inhibition of T cell proliferation by NO may be prevented by simultaneous NADPH oxidase activity.