A Rapid bioassay to monitor murine leukemia virus infection in mice using cellular gp71 binding

A rapid and sensitive bioassay based on the availability of cell surface receptors for the binding of purified envelope glycoprotein, gp71, of Rauscher murine leukemia virus (R-MuLV) was developed to serially monitor viral-induced leukemogenesis in individual BALB/cAnN mice. The specificity of the bioassay was demonstrated by the competition of [ 125I]gp71 cellular binding with murine ecotropic viruses, purified unlabelled R-MuLV envelope glycoprotein and by antiserum to R-MuLV gp71. In contrast, there was no effect on the [ 125I]gp71 binding level with the addition of murine xenotropic viruses, R-MuLV p30, or several other proteins. The [ 125I]gp71 binding level of circulating leukocytes was significantly ( P < 0.05) reduced in mice after R-MuLV infection. The reduction of cellular gp71 binding developed in two stages and the latter stage was highly dependent ( P < 0.05) on circulating infectious virus titer. Using this technique, the gp71 cellular binding levels of 48–60 individual mice can be assayed in a 4 h period. The advantages of this bioassay compared to standard immunological and tissue culture techniques used in studying retrovirus expression and viral—cell interactions are discussed.