Subcellular Representation of Murine Thymus-Leukemia (TL) Antigens in Phenotypically TL+ and TL- Cells

Abstract

The subcellular representation of thymus-leukemia (TL) antigens in murine cells was studied by inhibition of cytotoxic antiserum. By differential centrifugation, subcellular fractions were obtained from 6 sources: thymocytes of B6 mice (TL^-); thymocytes of a congenic mouse line (B6-TL⁺) differing from B6 at the Tla locus; a TL⁺ B6 leukemia (ERLD); a TL^-B6 leukemia (E♂ G2); and liver cells from B6 and B6-TL⁺ mice. Only fractions obtained from the phenotypically TL⁺ sources, i.e., B6-TL⁺ thymocytes or ERLD leukemia cells contained TL antigen. Plasma membranes were most active, followed by mitochondria and microsomes. Nuclear and cytosol fractions contained no intrinsic activity. These results suggest that the phenotypic expression of TL antigens is not a question of selective expression at the cell surface but reflects instead repression vs derepression at the level of the genome.