Thymectomy does not affect tumour rejection and cytophilic activity in a murine allogeneic lymphoma model

An experimental model was devised in which an AKR lymphoma is conditioned to grow in BALB mice leading to reproducible tumor incidence which makes tumor-bearing (progressor) and tumor-rejecting (regressor) animals simultaneously available. The object of this paper was to determine the effect of neonatal thymectomy (xT) on allogeneic tumor incidence and on anti-tumor cytophilic activity. The latter was determined by the adherence of lymphoma cells to guinea pig peritoneal macrophages previously incubated with preheated mouse serum. The results obtained, in 2-3 month old animals, show no difference in lethal tumor incidence between xT and intact mice, 36% (14/39) vs. 39% (14/36). Neither did xT alter the significant increase in cytophilic antibodies detected in regressor serum, 115 +/- 15 (S.E.) vs. 106+/- 22 0/00 macrophages bearing tumor cells as compared to control values in either xT or normal serum, 53 +/- 3 vs 52 +/- 3. This background cytophilic activity was not significantly altered in progressor serum of either xT or intact mice, 36 +/- 5 vs 65 +/- 6. The specificity of the antitumor cytophilic antibodies was determined by the negative results obtained when a different tumor was used as target cell. It can be concluded that ant-tumor cytophilic antibodies are detectable in regressor but not in progressor serum. Thymectomy in this model does not alter either in vivo tumor incidence or humoral cytophilic activity. Since no thymic remnants were encountered at autopsy, it is postulated that AKR lymphoma cells, which proved to be neoplastic T cells, are capable of rendering T-immunocompetent a thymectomized allogeneic BALB host.