Given the highly conserved nature of invariant Natural Killer T (iNKT) cells and CD4⁺CD25⁺FOXP3⁺ regulatory T cells (Tregs) among species, our goal was to assess the in vivo reciprocal crosstalk between these cells in TNF driven arthritis. First, we evaluated iNKT responses under steady state conditions in DEREG mice allowing conditional Treg depletion by injection of diphtheria toxin. In the absence of Tregs, there was a significantly increased cytokine release induced by α-GalCer, along with a more robust expansion of iNKT cells in liver and spleen. We next examined the cooperation of iNKT cells and Tregs under conditions of high TNF load which leads to arthritic disease, with many features of human spondyloarthritis. To this end, we backcrossed DEREG and Jα18^-/- mice with TNF^∆ARE mice, and evaluated onset and progression of peripheral arthritis in TNF^∆ARE DEREG mice versus Jα18^-/- TNF^∆ARE DEREG mice by clinical scoring, histopathology and microCT.  Lack of iNKT cells in Jα18^-/-TNF^∆AREmice was found to result in a substantial increased disease progression as compared to TNF^∆ARE mice. Rather unexpectedly, Treg depletion did not cause worsening of arthritis in both TNF^∆ARE  as well as Jα18^-/- TNF^∆ARE mice. Evaluating Treg features in these mice into detail, we found that Treg frequencies in lymphoid organs of TNF^∆ARE mice were increased and they showed an altered phenotype, which was even more pronounced in the iNKT deficient TNF^∆ARE mice. Moreover, while conventional T cell proliferation was suppressed by Tregs isolated from joint- and gut-draining lymph nodes of TNF^∆ARE mice and Jα18^-/- TNF^∆ARE mice,  inhibition of cytokine production  was markedly affected. Taken together, our findings highlight an important regulating role for iNKT cells in TNF driven forms of arthritis, independent of a Treg crosstalk. Furthermore, our results indicate that Treg cells are particularly prone to functional modulation under conditions of high TNF load.