Neutralization of homologous and heterologous oncornaviruses by antisera against the p15(E) and gp71 polypeptides of Friend murine leukemia virus

Abstract

Antisera prepared in rabbit or goat against the purified polypeptides of Friend murine leukemia virus (F-MuLV) were tested in neutralization tests against homologous F-MuLV, Gross (G−) MuLV, murine xenotropic virus (MuX), and feline leukemia virus (FeLV). Antisera directed against p10 and p30 did not neutralize; anti gp71 sera were strongly neutralizing for F-MuLV, MuX, and G-MuLV. The last virus was somewhat less sensitive. Heated anti gp71 sera were as active against the murine viruses as the unheated sera. FeLV was neutralized by unheated, fresh anti gp71 sera, albeit somewhat more weakly than mouse viruses. Although heating of the anti gp71 serum removed its neutralizing potency for FeLV, it could be generally restored by the addition of complement. Neutralization of two other nonmurine oncornaviruses by anti gp71 serum resembled that of FeLV. Neutralization kinetic curves and multiplicity curves were done with anti gp71 serum and F-MuLV, G-MuLV, and MuX. These resembled analogous curves obtained with other animal viruses. When the anti gp71 serum was fractionated, the 7 S IgG fraction contained essentially all the neutralizing antibody. Anti p15(E) serum did not neutralize homologous F-MuLV or the other ecotropic G-MuLV. It was able to neutralize MuX and FeLV, but only in the presence of complement. The slopes of the kinetic curves obtained with MuX and the anti p15(E) serum showed a dependency on both the antibody concentration and complement. The combination of the anti p15(E) and anti gp71 sera with and without complement generally showed simple additive effects except that a combination of the heated sera could neutralize FeLV in the absence of added complement. The specificity of neutralizing antibody was examined by reciprocal cross-absorptions of sera with respective purified antigens. The gp71 polypeptide completely absorbed the anti gp71 neutralizing antibody for MuX and FeLV, whereas the p15(E) antigen was without effect. Reciprocally the p15(E) antigen removed neutralizing antibody for MuX and FeLV from anti p15(E) sera while the gp71 polypeptide was inactive. Purified F-MuLV absorbed the neutralizing activity of both antisera confirming that gp71 and p15(E) are surface antigens. As a corollary, some complex anti FeLV sera could neutralize MuX as well as FeLV. This activity for MuX was heat-stable and could be specifically abrogated by F-MuLV gp71 antigen but not the p15(E) antigen. These data demonstrated that potent and functional neutralizing antibody could be elicited against the group- and interspecies-specific determinants of two oncornavirus surface components.