Invariant natural killer T (iNKT) cells represent a particular subset of T lymphocytes capable of producing several cytokines, which exert regulatory or effector functions, following stimulation of the T cell receptor. In this study, we investigated the influence of iNKT cells on the development of experimental anti-glomerular basement membrane glomerulonephritis (anti-GBM GN). After injection of anti-GBM serum, the number of kidney iNKT cells rapidly increased. iNKT cell-deficient mice (J alpha 18(-/-)) injected with anti-GBM serum demonstrated worse renal function, increased proteinuria, and greater glomerular and tubular injury compared with similarly treated wild-type mice. We did not detect significant differences in Th1/Th2 polarization in renal tissue that might have explained the severity of disease in J alpha 18(-/-) mice. Interestingly, expression of both TGF-beta and TGF-beta-induced (TGFBI) mRNA was higher in wild-type kidneys compared with J alpha 18(-/-) kidneys, suggesting a possible protective role for TGF-beta in anti-GBM GN. Administration of an anti-TGF-beta neutralizing antibody significantly enhanced the severity of disease in wild-type, but not J alpha 18(-/-), mice. In conclusion, in experimental anti-GBM GN, iNKT cells attenuate disease severity and TGF-beta has a renoprotective role.