In particular, the investigators identified two dominant autoreactive TCRs: TCR 7-39 and TCR 6-39. They then transferred the genes for the TCR 7-39 and TCR 6-39 into Rag2-/- mice, which lack mature T and B cells. They, thus, engineered retrogenic 7-39 (R7-39) Rag2 -/- and R6-39 mice that were populated with 7-39 and 6-39 TCR-transduced cells, respectively. Both mice strains spontaneously developed arthritis. The investigators next transferred T cells from the R7-39 mice into Rag2-/- mice and demonstrated that the autoreactive T cells were able to transfer both arthritis and dermatitis. The authors concluded that CD4+ T cells with a specific TCR mediate autoimmune arthritis and dermatitis in mice.
Ubiquitous Cellular Protein
The researchers next created T cell hybridomas that expressed either the 7-39 TCR or the 6-39 TCR. They used the hybridomas to identify the target self antigen. They found that the 7-39 TCR recognized the ubiquitously expressed 60S ribosomal protein L23a (RPL23A). The 6-39 TCR did not, however, bind to peptides derived from RPL23A. The authors hypothesized from this that RPL23A is one of the target antigens in patients with arthritis as well as dermatitis. Their results also suggest that more than one systemic antigen can underlie the induction of arthritis.
The investigators demonstrated that RPL23A was able to stimulate CD4+ T cells in the mice via RPL23A-derived peptide-MHC class II complexes. In addition, transfer of CD4+ T cells, but not sera from B cell-reconstituted R7-39 mice, was able to induce arthritis in Rag2-/- mice. Regulatory T (Treg) cells from either regular BALB/c mice or BALB/c SKG mice were not able to suppress the development of arthritis when cotransferred with 7-39 TCR+ CD4+ T cells.
The team next examined the role of RPL23A in humans. They found that RPL23A mRNA was ubiquitously expressed in healthy human tissues. Moreover, T cells and autoantibodies from patients with RA reacted to the RPL23A antigen.
“Our results show that by attenuating TCR signal intensity in developing T cells (hence reducing their sensitivity to thymic negative selection by natural self ligands), T cells reactive with ubiquitously expressed self antigens can be generated as dominant pathogenic clones causing systemic autoimmune disease. Because similar attenuation of TCR signaling at various degrees in conjunction with Treg cell depletion is able to produce a variety of other autoimmune diseases in mice, this strategy of generating pathogenic T cells and characterizing the self antigens they recognize would facilitate our understanding of the mechanisms of other autoimmune diseases of currently unknown etiology. In addition, given that genetic polymorphism in a signaling molecule in T cells is a major determinant of genetic susceptibility to various human autoimmune diseases including RA, such a genetic variation might, at least in part, alter thymic selection, hence forming a TCR repertoire for causing autoimmune disease,” wrote the authors in their paper.