T‐cell and natural killer cell development in thymectomized Xenopus

Abstract

Summary: The Xenopus early‐thymectomy model system is used to investigate the extent to which the thymus controls T‐cell development and to probe the evolution of natural killer (NK) ceils. Loss of T‐cell function following thymectomy, together with the paucity of cells expressing monoclonal antibody‐defined T‐cell surface markers, and greatly reduced expression of T‐cell receptor β transcripts in spleen, ever and intestine, indicate that T‐cell development is minimal in the absence of the thymus. Our findings therefore mitigate against the idea that a substantial extrathymic pathway of T‐cell development exists in early vertebrate evolution. Rather, they suggest that in this amphibian representative T cells are predominately thymus dependent. In vitro studies with control and thymectomized Xenopus splenocytes reveal that a non‐T/non‐B population and also two T‐cell subsets all display natural cytotoxicity towards allogeneic thymus lymphoid tumour cells (which are deficient in MHC antigen expression). Since Xenopus thymectomized early in larval development are permanently deficient in T cells, they may provide a useful phylogenetic model for the study of NK cells.