Macrophage and lymphocyte-depleted thymus reticuloepithelial cell cultures: establishment and functional influence on T-lymphocyte maturation, C-type virus expression and lymphomatous transformation in vitro.

A method of cultivation has been developed that yields thymus reticuloepithelial (TRE) cell monolayers composed almost entirely of epithelial-like cells, with no detectable macrophages or lymphocytes. These cultures show the capacity to induce responsiveness to lectin mitogens in immature thymocytes. Such monolayers induce Thy-1 expression in nude mouse spleen and bone marrow cells. The functional macrophage-lymphocyte depleted TRE monolayers can be cryptically infected by radiation leukemia virus (RadLV). However, RadLV-infected TRE cells lack the capacity to induce neoplastic transformation in normal weanling and newborn thymocytes. Cultures prepared from C57BL/Ka mice treated with a leukemogenic course of irradiation produce a B-fibrotropic nonleukemogenic virus, and normal thymocytes cocultivated with these monolayers do not undergo in vitro transformation. It is concluded that TRE monolayers depleted of macrophages and lymphocytes: (1) exhibit the functional capacity to induce some of the properties of mature T cells; (2) are infectable by RadLV; (3) are one of the sites for expression of ecotropic virus after leukemogenic fractionated irradiation; and (4) are not capable of transforming normal thymocytes in vitro.