Specificities of human immunoglobulins reactive with antigens in preparations of several mammalian type-C viruses

Abstract

Human serological reactivity with type-C RNA tumor viruses was assessed. Probes consisted of radioactively labeled, gradient purified Woolly monkey-derived simian sarcoma virus-simian sarcoma-associated virus (SSV-SSAV), Rauscher murine leukemia virus (R-MuLV), feline leukemia virus (FeLV-AB), and Rous-associated virus (RAV-2). Most human sera, surveyed for precipitating reactivity against intact virus (1 μg protein) by means of a sensitive radioimmuno-precipitation (RIP) assay, were found to precipitate type-C viruses of simian, murine, and feline, but not avian, origin with the reactivity primarily due to immunoglobulin G. No clear differences in reactivity between sera from normal individuals and from those with various neoplasms were found in preliminary surveys. Specificity tests were performed primarily with SSV-SSAV. Absorption studies with sheep and human red blood cells and blood-typing sera excluded involvement of known blood-group substances or Forssman-like antigens in assays with SSV-SSAV. Quantitative absorption tests with fetal calf serum proteins showed some removal of reactivity from several human sera, but only to maximum levels of 20–45% competition. Reactivity of human serum with SSV-SSAV was completely removed by preabsorbing with 2–4 × 106 tissue culture cells producing SSV-SSAV or SSAV while normal cells and SSV- or Kirsten murine sarcoma virus-transformed nonproducer cells showed no absorption capacity at 10-fold higher concentrations. Complete absorption of reactivity could also be achieved with a 70,000 molecular weight fraction from purified virus while fractions containing p30, p14, or p12 had negligible effects. Direct titering of human sera for reactivity with purified viral gp70 in radioimmunoassays, however, proved negative. The relationship between the latter results and those of the competition experiments are discussed.