Cytotoxic T lymphocytes specific for murine type II collagen do not trigger arthritis in B10 mice

T-bet represses collagen-induced arthritis by suppressing Th17 lineage commitment through inhibition of RORγt expression and function

T-bet is a key transcription factor for the T helper 1 lineage and its expression level is negatively correlated to inflammation in patients with rheumatoid arthritis (RA). Our previous study using T-bet transgenic mice revealed over-expression of T-bet completely suppressed collagen-induced arthritis (CIA), a murine model of RA, indicating a potential suppressive role of T-bet in the pathogenesis of autoimmune arthritis. Here, we show T-bet-deficiency exacerbated CIA. T-bet in CD4 + T cells, but not in CD11c + dendritic cells, was critical for regulating the production of IL-17A, IL-17F, IL-22, and TNFα from CD4 + T cells. T-bet-deficient CD4 + T cells showed higher RORγt expression and increased IL-17A production in RORγt-positive cells after CII immunization. In addition, T-bet-deficient naïve CD4 + T cells showed accelerated Th17 differentiation in vitro. CIA induced in CD4-Cre T-bet^fl/fl (cKO) mice was more severe and T-bet-deficient CD4 + T cells in the arthritic joints of cKO mice showed higher RORγt expression and increased IL-17A production. Transcriptome analysis of T-bet-deficient CD4 + T cells revealed that expression levels of Th17-related genes were selectively increased. Our results indicate that T-bet in CD4 + T cells repressed RORγt expression and function resulting in suppression of arthritogenic Th17 cells and CIA.

CD4 and CD8 T cells in susceptibility/protection to collagen-induced arthritis in HLA-DQ8-transgenic mice: implications for rheumatoid arthritis

To investigate the role of CD4 and CD8 T cells in arthritis, we generated transgenic mice deficient in CD4 and CD8 molecules expressing RA-susceptible gene HLA-DQ8. DQ8.CD4(-/-) mice were resistant to developing collagen-induced arthritis (CIA). However, DQ8.CD8(-/-) mice developed CIA with increased incidence and more severity than DQ8 mice. Both DQ8.CD8(-/-) and DQ8 mice produced rheumatoid factor. In addition, DQ8.CD8(-/-) mice produced antinuclear Abs. The B cell compartment and expression of DQ8 were normal in all the strains, although frequency of cells expressing DQ8 was less in CD4(-/-) mice. An increased frequency of CD3(+) double-negative (DN) T cells was found in DQ8.CD8(-/-) compared with DQ8.CD4(-/-) and DQ8 mice. These CD3(+) DN T cells produced high amounts of IL-10 in CD8-deficient mice. Analysis of cell division using a cell cycle tracking dye showed a higher rate of division of CD3(+) and CD3(+) DN T cells in DQ8.CD8(-/-) mice compared with DQ8.CD4(-/-) and DQ8 mice. Decreased apoptosis was seen in CIA-susceptible DQ8 and CD8-deficient mice, indicating a defect in activation-induced cell death. These observations suggest that CD4 cells are necessary for initiation of CIA in DQ8 mice. We hypothesize that CD8(+) T cells are not capable of initiating CIA in DQ8-transgenic mice but may have a regulatory/protective effect.

Influence of CD4 or CD8 deficiency on collagen-induced arthritis

The role of T cells in the mouse collagen-induced arthritis (CIA) model for rheumatoid arthritis is not clarified, and different results have been reported concerning the role of CD4 and CD8 T cells. To address this issue, we have investigated B10.Q mice deficient for CD4 or CD8. The mice lacking CD4 were found to be less susceptible to disease, but not completely resistant, whereas the CD8 deficiency had no significant impact on the disease. No difference in the development of late occurring relapses was noted. Interestingly, the CD4-deficient mice had a severely reduced response to the glycosylated form of the immunodominant type II collagen (CII) 256-270 peptide whereas the response to the non-glycosylated peptide was not significantly different. Furthermore, CD4-deficient mice had lower antibody responses to CII, explaining the lower disease susceptibility. In comparison with previously reported results, it is apparent that the lack of CD4 molecules has a different impact on CIA if present on different genetic backgrounds, findings that could possibly be related to the occurrence of different disease pathways of CIA in different mouse strains.

Phosphorylated Peptides Can Be Transported by TAP Molecules, Presented by Class I MHC Molecules, and Recognized by Phosphopeptide-Specific CTL

CTL recognize short peptide fragments presented by class I MHC molecules. In this study, we examined the effect of phosphorylation on TAP transport, binding to class I MHC molecules, and recognition by CTL of peptide fragments from known phosphorylated oncogene proteins or virus phosphoproteins. We show that phosphopeptides can be efficiently transported from the cytosol to the endoplasmic reticulum by the TAP. Furthermore, we show that phosphorylation can have a neutral, negative, or even a positive effect on peptide binding to class I MHC. Finally, we have generated phosphopeptide-specific CTL that discriminate between the phosphorylated and the nonphosphorylated versions of the peptide. We conclude that phosphopeptide-specific CTL responses are likely to constitute a subset of the class I MHC-restricted CTL repertoire in vivo.