Exogenous Thy-1.1 expression as a marker for thymocyte maturation in transgenic mice.

We established a line of transgenic mice carrying the exogenous mouse Thy-1.1 gene (8.2 Kb Eco RI genomic DNA fragment). In these mice, Thy-1.1 was expressed on thymocytes but not on peripheral T cells, presumably due to the lack of cis-acting element(s) on the microinjected genomic DNA. Even in the thymus, however, while most of the CD3/TCR- thymocytes were positive for the transgenic Thy-1.1 gene expression, the CD4+ or CD8+ single positive (SP) thymocytes were composed of two groups, one Thy-1.1+ and one Thy-1.1-, suggesting that the former belongs to cells at premature stages of terminal T cell differentiation. There was no difference in the amount of CD3/TCR complexes expressed on two such SP thymocyte subsets. In the double negative (DN) thymocytes, all the CD3/TCR+ cells were Thy-1.1-. These results suggest that the maturational process of CD3+ DN thymocytes differs from that of SP thymocytes. The unique distribution of Thy-1.1+ population among CD3+ thymocytes suggests that the transgenic Thy-1.1 gene expression can serve as a useful marker to examine terminal maturation processes of CD3+ thymocytes.