SUMMARYTo investigate the role of B cells in the development of CIA, a model for rheumatoid arthritis, we investigated susceptibility to CIA in mice lacking B cells due to the deletion of the IgM heavy chain gene (mMT). The mMT deletion was backcrossed into two different CIA-susceptible strains, B10.Q and B10.RIII. Two different variants of the CIA model are inducible in these strains: in B10.Q with rat type II collagen (CII) and in B10.RIII with bovine CII. Homozygous deletion of the IgM gene led to the absence of B cells and dramatically reduced immunoglobulin levels compared with wild-type mice. The deletion of IgM totally abrogated development of CIA in both strains, although the anti-CII T cell response did not differ between the mMT and wild-type controls. We conclude that B cells play a crucial role in the development of CIA.

B10.RIII mice develop chronic and relapsing experimental autoimmune encephalomyelitis (EAE) after immunization with the myelin basic protein (MBP) peptide 89-101. The disease is associated with the major histocompatibility complex (MHC) (eae1). We have now investigated the importance of non-MHC regions for the EAE susceptibility in a cross between RIIIS/J and B10.RIII mice which share the MHC region but differ in disease susceptibility. Linkage analysis using microsatellite markers spanning the genome identified a region (eae2) on chromosome 15 which showed linkage to disease (P = 0.0002). Our data also suggest linkage to a second region (eae3) on chromosome 3 (P = 0.0024), and provide evidence for locus interactions between eae2 and eae3. These results provide clues to the genetic basis of multiple sclerosis.

The genetic susceptibility to collagen-induced arthritis (CIA) in mice, the most commonly used model for rheumatoid arthritis, has been analyzed. The highly susceptible B10.RIII strain was crossed with the resistant RIIIS/J strain and the F2 intercross mice were subjected to genomic screening using microsatellite markers. These strains share the MHC region on chromosome 17, known to be of importance in CIA (this locus is named Mcia1). The same cross has earlier been used to map the major genes outside the MHC controlling chronic relapsing experimental allergic encephalomyelitis (EAE). It was found that the major locus controlling CIA (Mcia2; lod 4.12) was located on chromosome 3 in the same region as one of the major loci controlling EAE (Eae3). The linkage was reproduced in a mouse strain in which the locus was isolated on the B10.RIII background at the N4I2 generation. A second putative locus was identified on chromosome 13 (lod 3.13). The present finding identifies new loci outside the MHC controlling CIA and provides evidence that mouse CIA is controlled by polymorphic genes.

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RORγt, an isoform of the retinoic acid-related orphan receptor gamma (RORc, RORγ), has been identified as the master regulator of T-helper 17 (TH 17) cell function and development, making it an attractive target for the treatment of autoimmune diseases. Validation for this target comes from antibodies targeting interleukin-17 (IL-17), the signature cytokine produced by TH 17 cells, which have shown impressive results in clinical trials. Through focused screening of our compound collection, we identified a series of N-sulfonylated benzoxazepines, which displayed micromolar affinity for the RORγ ligand-binding domain (LBD) in a radioligand binding assay. Optimization of these initial hits resulted in potent binders, which dose-dependently decreased the ability of the RORγ-LBD to interact with a peptide derived from steroid receptor coactivator 1, and inhibited the release of IL-17 secretion from isolated and cultured human TH 17 cells with nanomolar potency. A cocrystal structure of inverse agonist 15 (2-chloro-6-fluoro-N-(4-{[3-(trifluoromethyl)phenyl]sulfonyl}-2,3,4,5-tetrahydro-1,4-benzoxazepin-7-yl)benzamide) bound to the RORγ-LBD illustrated that both hydrophobic interactions, leading to an induced fit around the substituted benzamide moiety of 15, as well as a hydrogen bond from the amide NH to His479 seemed to be important for the mechanism of action. This structure is compared with the structure of agonist 25 (N-(2-fluorophenyl)-4-[(4-fluorophenyl)sulfonyl]-2,3,4,5-tetrahydro-1,4-benzoxazepin-6-amine ) and structures of other known RORγ modulators.