Implications of TL Phenotype Changes in an H-2-Loss Variant of a Transplanted H-2 b /H-2 a Leukemia

An H-2-loss variant line, lacking H-2(a) antigens, was obtained from an H-2(b)/H-2(a) (C57BL x A)F(1) transplanted leukemia by immunoselection. The TL phenotype of the unselected line was TL.1,2,3,4 and that of the variant TL.1,2,4, which is the phenotype of TL(+) leukemias of C57BL. This finding, and the observed quantitative alterations of antigens TL.1,2 and 4, indicate that the Tla (Thymus leukemia antigen) locus was functionally deleted together with the H-2 locus in the process of variant formation, despite absence of selection against cells carrying TL antigens. Representation of H-2 antigens of the remaining haplotype, H-2(b), was quantitatively unchanged.