Preliminary characterization of isoimmunogenic placental antigens in the rabbit

By isoimmunization of adult virgin female rabbits with rabbit placental extracts we have demonstrated the production of humoral antibody against two antigens, Ag-1 and Ag-2. Neither antigen is a normal serum protein, nor are they allotype proteins. Ag-1 has an alpha-2 mobility and a molecular weights of about 400,000. Ag-2 exhibits a gamma mobility but was not characterized. The antibody activity directed to Ag-1 in immune sera was the complement-fixing IgG fraction. Direct fluorescence-labeled antibody technique revealed that Ag-1 is a ubiquitous intracellular antigen primarily localized in the nucleus. The fast-growing, SV-40 virus-transformed rabbit kidney cell line (TRK-1) expressed much higher levels of Ag-1 than the slow-growing, non-transformed normal rabbit kidney cell line (LLC-RK1). The possibility that elevation of Ag-1 production is associated with rapid cell proliferation is discussed.