Absence of ecotropic or recombinant murine leukaemia virus in preleukaemic and leukaemic X-irradiated NZB mice

Expression of an endogenous retroviral transcript is associated with murine lupus

We have been investigating whether murine lupus is associated with endogenous type C retroviral expression. We used Northern blot analyses and oligonucleotide probes, which are able to distinguish the envelope genes of the xenotropic and mink cell focus-forming (MCF) classes of type C retroviruses. Xenotropic expression in the spleen varied markedly among inbred mouse strains; although all strains expressed a 1.8-kb transcript, only one-half expressed one or more larger transcripts (8.4, 7.2, and/or 3.0 kb). Autoimmune disease did not correlate with expression of any of the xenotropic transcripts. Xenotropic and MCF transcripts were expressed independently among the mouse strains studied. Splenic RNA from all strains contained 7.2-, 3.0-, and 1.8-kb MCF transcripts. Some strains also expressed 8.4-kb MCF splenic RNA. There was a strong association between murine lupus and expression of 8.4-kb MCF transcripts: 6 of 6 lupus-prone strains, but only 2 of 11 nonautoimmune strains, had detectable 8.4-kb MCF RNA. The xid and Yaa mutations had minimal effects on expression of 8.4-kb MCF-related transcripts, despite their major and opposite effects on disease. Moreover, New Zealand black mice highly expressed this RNA from day 1 of life, before disease development. The data suggest that expression of 8.4-kb MCF endogenous retroviral transcripts is a primary feature of murine lupus and is not secondary to disease expression.

Involvement of peritoneal macrophages and spleen stromal cells in X-irradiation-induced reticulum cell neoplasms in C57BL/6 mice

Some correlation was observed between the occurrence of FA-positive PE-MO and spleen stromal cells (removed from X-irradiated RCN-bearing old-adult B6 mice) and the generation of RCN. No significant correlation was found between the viral content of lymphoid organs from the same mice and the occurrence of RCN. The main viral particle detected in lymphoid organs from radiation-induced RCN-bearing mice was the xenotropic virus. Ecotropic viruses were detected in a few spleens and Payer patches from such mice. These ecotropic viruses showed very poor lymphomagenic activity and required 400R X-ray as a cofactor. No dualtropic viruses were detected. However, inoculation of ecotropic (SFA2) helper virus to X-irradiated old-adult B6 mice, resulted in an efficient rescue of lymphomagenic viruses, enriched with phenotypically mixed, dualtropic viruses. Some of these DT viral preparations were cloned and seemed to consist mainly of xenotropic sequences. Thus, inoculation of helper viruses influenced the generation and selection of DT viruses. Such viral preparations, enriched with DT viruses, had a better lymphomagenic activity compared to endogenous ecotropic viruses, isolated from radiation-induced RCN-bearing mice. Indirect evidence suggested the involvement of a defective (xenotropic and possibly adjacent cellular genes) particle in lymphoma induction. To conclude, a possible mechanism for the development of radiation-induced RCN is suggested, emphasizing the role of MO in such a process.

Time course of C-type retrovirus expression in mice submitted to osteosarcomagenic doses of 224radium

Virus particles with the biochemical properties of C-type retroviruses appeared transiently in bone tissues of (C3H x 101) f1 hybrid mice early after treatment with 224 Radium; such particles were then again detected in the bones of the irradiated animals at the onset of osteosarcoma formation and in the osteosarcomas. Antibodies against a murine retrovirus isolated from a 224 Ra-induced osteosarcoma were produced and detected in the serum of the 224 Ra-treated animals within a month after treatment began. The antibody levels plateaued to a maximum after about 2 months and remained elevated until the tumors started to develop. The antibody concentration in the serum of these irradiated animals decreased then progressively to reach levels similar to those observed in untreated controls. It thus appears that the imminence of osteosarcoma development can be predicted by monitoring the anti-C-type virus antibody levels in the serum of the irradiated mice. These experiments also strongly suggest that treatment with 224Radium induces expression of endogenous viruses in the animals.