Cell surface receptors for ecotropic MuLV: detection and tissue distributions of free receptors in vivo.

The expression of available cell surface receptors for binding of the major envelope glycoprotein of Rauscher MuLV, gp71, was studied in freshly prepared tissues of the low-leukemic mouse strain CBA. The presence of such receptors is a requirement for infection and therefore also for transformation of cells in vitro by ecotropic MuLV. This paper describes the conditions of the binding assay for radiolabelled RLV gp71 and freshly prepared lymphoid cells under which binding occurs as a function of time and cell number. With this assay, available receptors for RLV gp71 were detected in all lymphoid as well as some non-lymphoid tissues, most notably brain. The lack of binding in other non-lymphoid tissues was not due to the presence of gp71 specified by endogenous ecotropic MuLV, as was determined by a sensitive group specific RIA. These results demonstrate that the distribution of receptor sites necessary for infection by ecotropic MuLV does not directly correlate with the tissue distribution of malignant transformation that is most commonly induced by these endogenous viruses. Therefore, susceptibility to infection by ecotropic MuLV, as determined by the expression of viral receptors, is not sufficient to determine the target organ for MuLV-induced oncogenesis.