TNFα and IL-1β in the synovial fluid facilitate mucosal-associated invariant T (MAIT) cell migration

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease that primarily affect the joints and inflammatory cell migration into inflamed articular sites contribute to this disease. Among the inflammatory cells, human mucosal-associated invariant T (MAIT) cells were recently recognized as critical cellular component with a pathological role in RA. However, their migratory characteristics are poorly understood. The aim of this study was to determine whether human MAIT cells preferentially traffick to inflamed synovial sites in rheumatoid arthritis patients and to elucidate the underlying mechanism. First, we found that TNFα and IL-1β were elevated in synovial fluid (SF) of RA patients, which resulted in increased expression of E-selectin, ICAM-1 and V-CAM-1 on blood vessel endothelial cells. To understand whether TNFα and IL-1β in the SF facilitated MAIT cell migration, we analyzed CD161⁺ TCRα7.2⁺ MAIT and other CD3⁺ T cells for differences in migratory capacity. Collectively, our results demonstrate that TNFα and IL-1β in the SF facilitated MAIT cell migration dependent on expression of selectin ligand, sialyl Lewis^X (sLe^X) and CCR6 on MAIT cells. We also showed that MAIT cells in the SF from RA patients equipped upregulated sLe^X compared to the peripheral blood of RA patients and healthy persons, which suggest that TNFα and IL-1β mediated expression of E-selectin preferentially attract sLe^X mediated MAIT cell migration into the SF of RA patients.