Isolation of two variants of dual ecotropic and xenotropic retrovirus from thymuses of mice inoculated as newborns with gross murine leukaemia virus

Abstract

Two variants of dual ecotropic and xenotropic retrovirus were isolated from thymuses of C3HeB/Fe mice inoculated as newborns with Gross passage A leukaemia virus (GPAV). The first variant, Th2P1, was isolated from a mouse having definite leukaemic symptoms and the second, Th4P1, was from a mouse in preleukaemic phase without leukaemic symptoms. Both viruses replicated as efficiently in mink cells as in mouse cells, for which they showed the same N tropism as GPAV. They did not trigger formation of syncytium in XC tests. Th2P1 virus induced foci of cytopathic effect in mink cells. Th4P1 virus possessed helper activities towards both S + L − mink and S + L − mouse cells and was neutralized significantly not only by antixenotropic virus serum but also by antiecotropic virus serum. Both viruses were devoid of leukaemogenic activity when inoculated into susceptible newborn mice. However, they accelerated significantly appearance of leukaemia in GPAV-infected C3HeB/Fe mice as well as in AKR mice. Recombinants between exogenous ecotropic GPAVs and activated endogenous xenotropic viruses were postulated. Deux variants de rétrovirus à la fois écotropes et xénotropes ont été isolés à partir de thymus de souris C3HeB/Fe inoculées à la naissance avec le virus de la leucémie murine de Gross, passage A (G-MuLV-PA). Ils se multiplient efficacement aussi bien dans les cellules de vison que dans les cellules de souris. Un des 2 variants isolés d'une souris leucémique induit la formation de foyers cytopathiques dans les cellules de vison. Les 2 virus sont dépourvus de pouvoir leucémogène lorsque des souriceaux nouveaunés sensibles sont inoculés avec ces virus. Néanmoins, ils accélèrent, de façon significative, l'apparition de la leucémie chez des souris C3HeB/Fe infectées par G-MuLV-PA ainsi que chez des souris AKR.