Inactivation of murine xenotropic oncornavirus by normal mouse sera is not immunoglobulin-mediated

Abstract

Several normal mouse sera were examined for their neutralizing potential against various leukemia viruses. All sera inactivated murine xenotropic oncornavirus (MuX). One of the sera also neutralized AKR murine leukemia virus (MuLV), whereas none neutralized feline leukemia virus. The inactivation of MuX was not associated with mouse immunoglobulins. The active factor was heat stable, dialysable, and remained in the supernatant fraction after immunoglobulin precipitation by ammonium sulfate. The kinetics of inactivation of MuX by mouse sera were complex and distinct from known immunoglobulin neutralization. Specific antisera against isolated mouse immunoglobulins did not reduce the inactivating capacity of these sera for MuX, although the neutralization of AKR-MuLV by one of these same sera was found to be mediated by immunoglobulin G. The specificity of this inactivation is unknown in that absorption of mouse sera with Friend MuLV gp71, p15(E), or intact ecotropic virus failed to affect MuX inactivation, whereas absorption of mouse sera with normal or virus-producing mouse or cat cells was able to remove the inactivating potential.