T cell receptor (TcR) β chain transgenic mice: Studies on allelic exclusion and on the TcR+ γ/δ population

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Abstract
To study allelic exclusion of TcR genes we analyzed two types (I and II) of TcR β transgenic mice. T cells derived from both types of mice contained similar amounts of transgenic RNA transcripts; however, surface expression of the transgenic β chain was drastically reduced in type II compared to type I. In type I transgenic mice, productive rearrangements and expression of endogenous TcR β genes were suppressed whereas on T cells of type II mice, both transgenic and endogenous TcR β chains were expressed on the surface of the same cell. These findings suggest that allelic exclusion of TcR genes in β transgenic mice depends on amount and/or onset of transgene expression during thymic development. Furthermore, TcR γ rearrangements and the population of TcR γ/δ‐bearing double‐negative CD4−CD8− thymocytes were reduced fivefold in type I transgenic animals. However, the Vγ usage and the γ/δ+ dendritic epidermal cell populations appeared normal. RNase protection analysis further revealed low levels of transgenic TcR β chain transcripts in TcR+ γ/δ CD4−CD8− thymocytes. These results suggest that the β transgene only quantitatively influences the γ/δ T cell compartment, and supports the independence of the γ/δ population.