MHC class II alleles associated with Th1 rather than Th17 type immunity drive the onset of early arthritis in a rat model of rheumatoid arthritis

Tuncel, Jonatan; Haag, Sabrina; Holmdahl, Rikard

Polymorphisms in the MHC class II (MHCII) genes are strongly associated with rheumatoid arthritis, supporting the importance of autoreactive T helper (Th) cells for the development of this disease. Here, we used pristane‐induced arthritis (PIA), induced by the non‐antigenic hydrocarbon pristane, to study the impact of different MHCII alleles on T‐cell activation and differentiation. In MHCII‐congenic rats with disease‐promoting MHCII alleles, pristane primarily induced activation of Th1 cells, whereas activated T cells were Th17 biased in rats with protective MHCII alleles. Neutralization of IFN‐γ during T‐cell activation abrogated the development of disease, suggesting that Th1 immunity is important for disease induction. Neutralization of IL‐17, by contrast, suppressed arthritis only when performed in rats with established disease. Adoptive T‐cell transfers showed that T cells acquired arthritogenic capacity earlier in strains with a prevailing Th1 response. Moreover, upon pristane injection, these strains exhibited more Ag‐primed OX40+ and proliferating T cells of polyclonal origin. These data show that T cells are polarized upon the first encounter with peptide‐MHCII complexes in an allele‐dependent fashion. In PIA, the polyclonal expansion of autoreactive Th1 cells was necessary for the onset of arthritis, while IL‐17 mediated immunity contributed to the progression to chronic disease.