G (Gross) and H-2 cell-surface antigens: location on Gross leukemia cells by electron microscopy with visually labeled antibody.

The hybrid-antibody method of locating cell-surface antigens in electron micrographs, with either ferritin or southern bean mosaic virus as the visual marker, was applied to the cells of a transplanted murine leukemia induced by Gross virus. The two antigens studied were (a) G (Gross) cell-surface antigen, which is a specific component of cells infected with Gross virus and is identified by cytotoxic hyperimmune C57BL/6 antiserum, and (b) H-2 antigen, which is the major histocompatibility determinant of the mouse. Both antigens were represented on the cell surface in discrete circumscribed areas. Neither antigen was present on free Gross virions or on virions in the process of budding from the cell surface. Thus G cell-surface antigen identified by C57BL mouse cytotoxic antiserum is not a constituent of the viral envelope, which accounts for the poor virus-neutralizing capacity of such antibody. Virus maturation may take place preferentially at regions of the cell surface where H-2 and G antigens are absent, for budding was seldom seen in H-2(+) sectors and never convincingly in G(+) sectors. In other experiments, serum from an untreated NZB mice aged 16 months gave labeling of the virion only, showing that this mouse strain, in contrast to C57BL and other strains, forms antibody to envelope antigen of Gross virus.