We have previously demonstrated that in vitro cell lines of mouse thymic
lymphomas express surface receptors specific for the retrovirus that induced them. This study extends these observations to an analysis of receptor-bearing cells in the preleukemic and leukemic phases of spontaneous AKR thymic lymphomagenesis. AKR mice regularly begin expressing N-tropic retroviruses (as assayed on NIH fibroblasts by the XC plaque assay) in several tissues early in life; thymic lymphocytes also express these viruses, but are not autonomously transformed. Later thymic
lymphomas emerge which are capable of metastasizing in the host of origin or transplanting
leukemias into syngeneic hosts. Just prior to the appearance of thymic
lymphomas, these mice also begin producing xenotropic retroviruses [as assayed in xenogeneic (For example, mink) fibroblasts], and concomitant with the appearance of the
leukemias is the appearance of "recombinant" retroviruses which cause mink fibroblast foci (MCF); these viruses express elements of both N- and X-tropic virus envelopes and N-tropic
viral gene products in their cores. Spontaneous AKR
leukemias also produce other retroviruses which do not cause XC plaques or mink fibroblast foci; these are called SL viruses. The subject of this study was to test whether in vivo thymocytes in the preleukemic and leukemic periods also bear receptors specific for N-tropic, recombinant MCF and SL AKR retroviruses. We demonstrated that each spontaneous thymic
lymphoma does bear receptors that bind viruses produced by the
lymphomas and MCF-247 to a high degree and that bind N-ecotropic AKR retroviruses less well. Thymic lymphocytes predominating in the preleukemic period do not express detectable levels of receptors for either of the viruses. In some mice, receptor-positive cells co-exist with receptor-negative cells; only the receptor-positive cells are capable of transplanting
leukemia to syngeneic hosts. We conclude that the presence of specific
cell surface receptors for
lymphoma cell-produced and recombinant AKR retroviruses is a marker for
leukemia in these hosts.