Protein A assay for mouse mammary tumor virus gp52 determinants on murine and human mammary tumor cells

Abstract

An isotopic staphylococcal protein A test (ISPAT) has been used to detect determinants of the mouse mammary tumor virus (MMTV) envelope antigen (gp52) on murine mammary tumor cells and to search for an immunologically related protein on the surface of established human mammary tumor cell lines. The substitution of fluorescein isothiocyanate-conjugated staphylococcal protein A (SPA) in assay for iodinated SPA demonstrated that gp52 detected on murine cells by adherent cell assay was predominantly membrane associated rather than cytoplasmic in nature. Swiss mouse embryo cells producing a C-type retrovirus (Moloney murine leukemia virus) were negative when assayed for gp52. Comparative assays (ISPATs) for gp52 cell surface determinants on human and murine mammary tumor cells did not demonstrate gp52-specific binding on five cell lines derived from human breast tumors and one derived from the milk of a lactating woman; however, parallel control GR mammary cultures, assayed on the same day, demonstrated the capability of the assay to detect gp52 determinants. Results indicated that this assay could have detected gp52 determinants on human cells at levels 1/11th to 1/60th of the amounts detected on murine cells.