Reconstitution of a T cell-dependent antibody response in the thymectomized clawed toad Xenopus laevis
Larvally thymectomized Xenopus laevis are unable to mount an antibody response to thymus-dependent antigens. In Chapter 2, larval thymuses incompatible at the major histocompatibility complex (MHO) (either irradiated or non-irradiated), and both MHC-compatible and incompatible "adult" thymuses implanted to thymectomized animals early in larval life, were found to restore cellular and serum antibody production to the thymus-dependent antigen sheep erythrocytes. Functional studies on thymocytes and splenocytes were carried out in Chapter 3 to determine whether thymocytes were relatively free from contaminating B cells and could be used as a "pure" source of T cells for cellular reconstitution experiments. It was shown that both thymocytes and splenocytes could be stimulated in vitro by the B cell nitrogen Escherichia coli lipopolysaccharide to differentiate into cytoplasmic immunoglobulin M-producing cells. Thus thymocytes were found to include a population of B lymphocytes. The experiments reported in Chapter 4 were designed to find a suitable method for the depletion of B cells from lymphocyte populations to be used for cellular reconstitution. Nylon wool filtration proved to be inefficient at depleting B cell numbers. However γ-irradiation was able to effectively remove B cell activity from unprimed lymphocyte populations. In Chapter 5, the ability of injected lymphocytes to migrate to the spleen was investigated. It was shown using (^51)Cr labelling and ploidy-marked cells that lymphocytes could reach the spleen within 6 hours after injection and remain there for at least 6 days. Finally, in Chapter 6, cellular reconstitution experiments showed that injection of thymocytes or splenocytes was not very effective in restoring the cellular antibody production of thymectomized animals to sheep erythrocytes. However splenocyte/peripheral blood lymphocyte mixtures, even after irradiation to remove functional B cells, were able to fully restore the cellular antibody response, irrespective of whether the injected cells were MHC-compatible or incompatible to the host. Thus it appears that the short-tem primary in vivo antibody response to sheep erythrocytes does not require MHC identity of the T and B lymphocyte populations.