MOLECULAR ANALYSIS OF SKEWED TCRA-V GENE USE IN T-CELL RECEPTOR BETA-CHAIN TRANSGENIC MICE

The influence of beta-chain diversity on the expressed T-cell receptor (TCR) alpha-chain repertoire was investigated using transgenic mice w hich exclusively express a single rearranged TCR beta-chain gene. Anal ysis of these mice using alpha-chain-specific recombinant cDNA librari es showed that expression of the transgene-encoded beta chain results in significant skewing in Tcra-V gene segment usage vs nontransgenic m ice. Skewing was most pronounced towards alpha chains using TCRA-V seg ments. 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 nont ransgenic T cells. Further analysis revealed that co-expression of Tcr a-V8 with Tcra-J24 in beta-transgenic mice is exhibited almost exclusi vely by CD4(+) T cells, and is associated with a limited number of clo sely related N-regions. Analysis of transgenic CD8(+) T cells demonstr ated predominant co-expression of Tcra-V8 with another Tcra-J (Tcra-J3 0), together with a different, limited N-region sequence. We conclude that the composition of expressed beta chains can profoundly influence the selection of companion alpha chains expressed in the periphery, a nd that alpha-chain N and J regions play a crucial role in discriminat ing 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 cons istent with a model for TCR structure in which the complementarity det ermining region (CDR)3 alpha domain participates in direct contact wit h the MHC.