AbstractObjectiveTo investigate the role of invariant natural killer T (iNKT) cells in TNFΔARE/+ mice, an animal model of spondylarthritis (SpA) with both gut and joint inflammation.MethodsThe frequency and activation of iNKT cells were analyzed on mononuclear cells from the lymph nodes and livers of mice, using flow cytometry with α‐galactosylceramide/CD1d tetramers and quantitative polymerase chain reaction for the invariant Vα14–Jα18 rearrangement. Bone marrow–derived dendritic cells (DCs) were obtained by expansion of primary cells with granulocyte–macrophage colony‐stimulating factor followed by coculture with iNKT cell hybridomas, and interleukin‐2 release into the cocultures was then measured by enzyme‐linked immunosorbent assay (ELISA). Cytokine levels were determined by ELISA or cytometric bead array analyses of freshly isolated DCs and iNKT cells in mixed cocultures. TNFΔARE/+ mice were backcrossed onto Jα18−/− and CD1d−/− mice, and disease onset was evaluated by clinical scoring, positron emission tomography, and histology. CD1d levels were analyzed on mononuclear cells in paired blood and synovial fluid samples from patients with SpA compared with healthy control subjects.ResultsIn the absence of iNKT cells, symptoms of gut and joint inflammation in TNFΔARE/+mice were aggravated. Invariant NKT cells were activated during the course of the disease. This was linked to an enrichment of inflammatory DCs, characterized by high levels of CD1d, particularly at draining sites of inflammation. A similar increase in CD1d levels was observed on DCs from patients with SpA. Inflammatory DCs from TNFΔARE/+ mice stimulated iNKT cells to produce immunomodulatory cytokines, in the absence of exogenous stimulation. Prolonged, continuous exposure, but not short‐term exposure, to tumor necrosis factor (TNF) was found to be responsible for the enhanced DC–NKT cell crosstalk.ConclusionThis mode of iNKT cell activation represents a natural counterregulatory mechanism for the dampening of TNF‐driven inflammation.