Rheumatoid arthritis is a complex disease associated with >100 risk loci, with the strongest association from the major histocompatibility complex (MHC) region. Here, we analyzed a new genetic association in the MHC class-III region (MHC-III) using adjuvant- and antigen-induced arthritis models. In addition, we used models for multiple sclerosis for comparison and dissected the MHC-III-mediated mechanisms of importance for antibody and T-cell responses to antigens. With the use of a panel of MHC-III recombinant inbred strains, we found that the 33-kb Ltab-Ncr3 haplotype in MHC-III was linked to the induction of arthritis with incomplete Freund's adjuvant, with similar effects in arthritis induced by several oil adjuvants (hexadecane, heptadecane, squalene, arlacel). Adoptive T-cell transfer experiment showed that this arthritis-protective effect operated during the priming of T cells by controlling their arthritogenicity. Interestingly, Ltab-Ncr3 did not regulate autoimmune diseases induced with tissue-specific antigens emulsified in adjuvant oils, such as collagen-induced arthritis or experimental autoimmune encephalomyelitis. No effect on antibody or T-cell response to tissue antigens in the Ltab-Ncr3 could be demonstrated. The finding that Ltab-Ncr3 is specific in regulating adjuvant-induced arthritis but not antigen-induced autoimmunity, and with unique effects on priming of autoreactive and arthritogenic T cells, provides new insight for understanding the regulation of autoimmune diseases.
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