Molecular analysis of skewed Tcra-V gene use in T-cell receptor β-chain transgenic mice

The influence of β-chain diversity on the expressed T-cell receptor (TCR) α-chain repertoire was investigated using transgenic mice which exclusively express a single rearranged TCR β-chain gene. Analysis of these mice using α-chain-specific recombinant cDNA libraries showed that expression of the transgene-encoded β chain results in significant skewing in Tcra-V gene segment usage vs nontransgenic mice. Skewing was most pronounced towards α chains using TCRA-V segments. Sequence analysis of Tcra-V8-containing genes from transgenic T cells revealed predominant use of a single Tcra-J segment (Tcra-J24), which was not detected in Tcra-V8 containing genes isolated from nontransgenic T cells. Further analysis revealed that co-expression of Tcra-V8 with Tcra-J24 in β-transgenic mice is exhibited almost exclusively by CD4+ T cells, and is associated with a limited number of closely related N-regions. Analysis of transgenic CD8+ T cells demonstrated predominant co-expression of Tcra-V8 with another Tcra-J (Tcra-J30), together with a different, limited N-region sequence. We conclude that the composition of expressed β chains can profoundly influence the selection of companion α chains expressed in the periphery, and that α-chain N and J regions play a crucial role in discriminating between class I vs class II major histocompatibility complex (MHC)-restricted recognition. Further, these results are in agreement with recent data concerning the crystal structure of the TCR, and most consistent with a model for TCR structure in which the complementarity determining region (CDR)3α domain participates in direct contact with the MHC.