Assessment of reactivities of natural antibodies to endogenous RNA tumor virus envelope antigens and virus-induced cell surface antigens

The autogenous humoral immune response of mice to their endogenous leukemia virus (MuLV) has been examined with respect to the reactivities of natural antibodies to MuLV envelope antigens and virus-induced cells surface antigens. The natural reactivity of MuLV envelope antigens was evaluated by means of a radioimmune precipitation assay of intact and disrupted virus, as well as by virus neutralization tests. The specificity of natural antibody for MuLV envelope antigens was determined by immunoelectron microscopy and radioimmune precipitation. Antibody reactivity to virus-induced cell-surface antigens was evaluated by immunoelectron microscopy and a complement-dependent cytotoxicity test. The strains of mice seleced for study were C57BL/6, C3H/Anf, and the C57BL/6 X C3H/Anf F1 hybrid. Although there were quantitative differences in the antibody levels among these various strains, the naturally recognized antigenic determinants of the virus were consistent, i.e., gp68, gp-43, and p15. High levels of neutralizing antibody against the xenotropic BALB:virus-2 were detected in these various normal sera with the focus reduction assay; however, only marginal levels of neutralizing activity against Moloney leukemia virus were detected with the XC virus assay. No anticellular antibody could be detected in these normal sera with the complement-dependent cytotoxicity assay.