Antibody directed against Friend leukemia virus stimulates DNA synthesis in a subpopulation of mouse B lymphocytes.

Goat and rat antisera directed against Friend leukemia virus (anti-FLV) were found to be B-lymphocyte mitogens stimulating DNA synthesis in these cells but not in T lymphocytes. Membrane fluorescence microscopy showed that anti-FLV reacts with a subset of B lymphocytes of which the majority express immunoglobulin mu chains. The mitogenic effect was found with all mouse strains tested including 129 and AKR. Absorption experiments with purified viruses indicated that the mitogenic effect is specific for an antigen present in murine leukemia viruses of the FMR subgroup. In absorption experiments with viable cells, the antigen involved in mitogenicity was found to be expressed on Friend erythroleukemia cell lines (4/4) and on myelomas (2/2) but not on normal thymus T lymphomas (0/2) or on rabbit or mink cells infected with BALB/c xenotropic virus. Preincubation of spleen cells with anti-gp70 antiserum inhibited the mitogenic effect of anti-FLV but not of lipopolysaccharide.