Functional activity of a transformed thymic epithelial cell line.

In an attempt to obtain pure populations of nonlymphoid thymic cells, monolayers of thymic cells enriched for low-density cells were transformed with SV40. This paper describes the characteristics of the initial cell lines which resulted from this approach. These cell lines appeared to be of epithelial origin by morphologic criteria (extensive surface microvilli and pronounced intercellular tight functions) and by biochemical analysis, since they possessed mouse keratin proteins. They did not possess I-region-associated antigens on their surface, markers that have been detected on normal thymic epithelium. Functionally, these transformed cell lines secreted a factor capable of inducing thymocytes to mature to functional cytotoxic effector cells directed against allogeneic stimulators. This factor did not appear to be interleukin 1, interleukin 2, or colony-stimulating factor; did not result in thymocyte proliferation; and did not affect peripheral T cells. The cell lines described in this report should prove useful in delineating the steps by which immature T cells acquire their immunocompetence in the thymus.