Phenotypic Suppression of H‐2 Antigens and Topography of the Cell Surface

Abstract

Mouse leukaemia EL4 and bone marrow cells sensitized with specific H‐2 antibodies could be made cytotoxicity‐resistant when incubated, before their exposure to complement, with rabbit‐anti‐mouse Ig at 37° C, but not at 0° C. The “modulated” cells gave a positive polar immunofluorescence with goat‐anti‐mouse Ig whose frequency was positively correlated with the degree of modulation. H‐2 heterozygous bone marrow cells were specifically modulated towards a hemizygous phenotype and tested in vivo for their relative capacities to form spleen colonies in syngeneic and semisyngeneic hosts. Their performances indicated a partial phenotypic suppression of the target antigens. By using alloantibodies directly conjugated with peroxidase, cellular distribution of H‐2 antigens was studied electronmicroscopically. In cells labelled at 37° C there were numerous peroxidase‐lined vacuoles whose formation could be traced back to engulfments of the outer cell membrane. At 0° C there was a continuous labelling of the cell surface. The data are discussed in regard to dynamics of the cell membrane and possible secondary changes induced by the antibody‐mediated attachment of a visual label.