EFFECT OF EARLY THYMECTOMY ON DEVELOPMENT OF RENAL TUMORS IN LUCKÉ TUMOR HERPESVIRUS-INFECTED LEOPARD FROGS

Abstract

The Lucké tumor of northern leopard frogs, Rana pipiens, provides an interesting model system to study development of tumors. It is relatively easy to induce renal tumors in metamorphosing frogs by injection of Lucké tumor herpesvirus (LTHV) into embryos, but it is difficult to induce tumors by injection of viruses into immunocompetent larvae or adults. We have begun to study whether debilitation of the thymus-dependent immune system during the larval period may affect tumor incidence in virus-infected frogs. Thymectomy (tx) at 2–3 weeks post-fertilization (Taylor-Kollros Stages II-III) reduced the number of splenic and blood lymphocytes, reduced in vitro lymphocyte responses to the mitogen, PHA, and prolonged survival of Lucké tumor implants. Thymectomy did not diminish in vitro responses to LPS, a T-independent mitogen (Rollins and Cohen, 1980). In spite of these significant reductions in T-cell responses measured in tadpoles 1–2 months post-thymectomy, tumor incidence in premetamorphic or metamorphosing frogs, injected as embryos with LTHV, was the same in thymectomized and normal immunocompetent animals. This suggests that: a) T-cell dependent immunity does not play a major role in the prevention of tumor development in immunocompetent larvae, and b) if tumor-specific transplantation antigens appear, they may induce tolerance rather than immunity in LTHV-injected frogs.