Immune response-associated antigens on mouse leukemia cells. I. Detection of Ia antigens on GRSL cells.

The expression of immune response-associated (Ia) antigens on the surface of mouse strain GR (H-2dx) ascites leukemia (GRSL) cell lines was studied by cytotoxic tests, immunofluorescence, and immunoprecipitation assays. Ia expression varied among the three GRSL cells lines (GRSL 2, GRSL 14, and GRSL 15) studied by cytotoxic assay. GRSL 14 cells showed the strongest expression of Ia antigens among these three cell lines. A time-course study of tumor growth in mice revealed that Ia antigens on the tumor cells demonstrated the strongest expression 10 days after injection of GRSL cells into GR mice, and that subsequently it decreased until the death of the animal. Cells treated with neuraminidase exhibited more readily detectable Ia antigens, expecially in the late stages of leukemia, which suggested that Ia antigens had been masked by sialic acid. Immunoprecipitation studies revealed that Ia molecules on the leukemia cell had the same molecular weight as those on the normal lymphocytes. Immunofluorescence studies disclosed that Ia antigens were distributed diffusely on the surface of the tumor cells.