Preferential use of a T cell receptor Vβ gene by acetylcholine receptor reactive T cells from myasthenia gravis-susceptible mice

Experimental autoimmune myasthenia gravis (EAMG) is an important model for testing current concepts in autoimmunity and novel immunotherapies for autoimmune diseases. The EAMG autoantigen, acethylcholine receptor (AChR), is structurally and immunologically complex, a potential obstacle to the application of therapeutic strategies aimed at oligoclonal T cell populations. Inasmuch as we had previously shown that the clonal heterogeneity of T cell epitope recognition in EAMG was unexpectedly limited, we examined TCR Vβ expression. AChR primed lymph node T cells and established AChR reactive T cell clones from EAMG-susceptible C57BL/6 (B6; H- 2^b, Mls-1^b) mice showed preferential utilization of the TCR Vβ6 segment of the TCR. After in vivo priming and in vitro restimulation for 7 days with AChR or a synthetic peptide bearing an immunodominant epitope, Vβ6 expressing lymph node cells (LNC) were expanded several-fold, accounting for up to 75% of recovered viable CD4⁺ cells. The LNC of B6.C-H-2^bm12 (bm12; H-2^bm12, Mls-1^b) mice, which proliferated in response to AChR but not to the B6 immunodominant peptide, failed to expand Vβ6⁺ cells. Inasmuch as nonimmune bm12 and B6 animals had similar numbers of Vβ6⁺ LNC (4-5%), this suggested that structural requirements for TCR recognition of Ag/MHC complexes dictated Vβ usage. Results concerning peptide reactivity and Vβ6 expression among T cells from (B6 x bm12)F₁ animals also suggested that structure-function relationships, rather than negative selection or tolerance, accounted for the strain differences between B6 and bm12. To examine the potential effects of thymic negative selection of Vβ6⁺ cells on the T cell response to AChR, CB6F₁ (H-2(bxd), Mls-1^b; Vβ6-expressing) and B6D2F₁ (H-2(bxd), Mls-1(axb); Vβ6-deleting) strains were analyzed for AChR and peptide reactivity and Vβ6 expression. Both F₁ strains responded well to AChR but the response of B6D2F₁ mice to peptide was significantly reduced compared to CB6F₁. Short and long term cultures of peptide-reactive B6D2F₁ LNC showed no expansion of residual Vβ6⁺ cells, although similar cultures of CB6F₁ LNC were composed of more than 60% Vβ6⁺ cells. The results from the F₁ strains further indicated that the T cell repertoire for peptide was highly constrained and that non-Vβ6 expressing cells could only partially overcome Mls-mediated negative selection of Vβ6⁺ TCR capable of recognizing peptide. Taken together, these studies clearly show that the expression of specific MHC and Mls molecules can dramatically affect the TCR repertoire for AChR.