Ecotropic and Xenotropic Type C Retroviruses Associated with Reticulum Cell Neoplasms of SJL/J Mice

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Abstract
An ecotropic type C retrovirus, the D1 murine leukemia virus (D1-MuLV), isolated from SJL/J mice was injected into neonatally thymectomized SJL/J mice. There was no acceleration of development of reticulum cell neoplasm (RCN) in these mice as compared with the control, uninoculated but similarly thymectomized group. The incidence of RCN at 10 and 11 mo. after injection was 14.6% and 12.5%, respectively. Two female mice inoculated with D1-MuLV developed mammary adenocarcinoma. There was persistence of high titers of the ecotropic virus associated with RCN and mammary tumor of SJL/J mice. Xenotropic virus (X-MuLV) was detected in spleens of normal SJL/J mice at ages 6 and 12 mo. (60% and 80%, respectively), but not at other ages. The X-MuLV isolated from SJL/J mouse embryo cell cultures treated with 5-iodo-2''-deoxyuridine (SJL-MEF-X-MuLV) and that isolated from a spontaneous RCN (SJL-RCN-X-MuLV) were compared with NZB-X-MuLV (NZB mouse origin) and AT124-X-MuLV (NIH Swiss mouse origin) in regard to their host range, ion and primer-template preference by reverse transcriptase, virus interference and neutralization characteristics. Cross-neutralization and gp70 competitive radioimmunoassays showed that D1-MuLV is more closely related to AKR-MuLV than to Rauscher-MuLV and appears to share some virus envelope antigens with SJL-X-MuLV. The type-specific gag gene product (p12) from Balb:virus-2 and NZB-X-MuLV was used in competitive radioimmunoassay, and SJL-RCN-X-MuLV was found to be more closely related to Balb:virus-2 (MuLV-X.alpha.) than to NZB-X-MuLV (MuLV-X.beta.).