Post-translational attainment of allelic exclusion of the T cell receptor α chain in a T cell clone

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Abstract
Two in-frame rearranged mouse TCR α chain genes from a single CD4+ T cell clone, MS202, specific for self-class II MHC antigen were transfected into a TCR-negative T cell hybridoma together with a β chain gene derived from the same T cell clone. Both α chain genes were efficiently transcribed and translated In the cytoplasm of host cells, but only one α chain (Vα5) was expressed on the cell surface in association with the partner β chain (Vβ4). The other α chain gene (Vα4) was translated into a mature form of the a chain but was unable to make a pair with the β chain, being prohibited from the surface expression. The supertransfection of the CD4 gene Into the α β transfectants did not alter the transcription and expression of both combinations of TCR α and β genes. The original self-class II reactivity was, however, reconstituted only in the cells expressing Vα5 and Vβ4 genes supertransfected with CD4. These results Indicate that the allelic exclusion of MS202 was achieved by a post-translatlonal mechanism where the product of an in-frame rearranged α chain was unable to be expressed on the cell surface, allowing further rearrangement and expression of the other α chain gene. The self-class II reactivity of TCR was dependent on the co-expression of CD4 molecules.

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