Effect of larval thymectomy on T-cell development and immunoglobulin class switch in Xenopus laevis (170.5)

Abstract

Abstract The gut associate lymphoid tissues (GALT) are the digestive tract’s immune system and play a crucial role in the evolution of the vertebrate adaptive immune system. Mammalian immunity depends on antibody production by B cells with T cell help. Our knowledge about adaptive immunity in cold blooded vertebrates is fragmentary. The frog Xenopus laevis is an ideal model for such studies. Amphibians were the first animals to evolve Ig isotype class switching. It is unclear if T cell help is phylogenetically more fundamental or class switch recombination. To determine whether T cell help is required for gut-specific IgX induction (assumed analogue of mammalian IgA) in X.laevis we need a model with no T -cells. We thymectomize 10-12 day tadpoles which provide us with a useful T -cell deficient model. Thymectomized tadpoles were monitored 15-20 days after surgery to check for any regrowth of thymus. TCR reverse transcriptase PCR was performed from peripheral blood of cleanly thymectomized animals. PCR results show there are no TCR α or γ mRNA transcripts in thymectomized frogs indicating that T-cell development is fully thymus dependent. Thymectomized animals validated by PCR will be orally immunized to test whether it will yield gut specific IgX response, and if IgX is T-dependent. Our preliminary experiments show higher induction of IgX in orally immunized animals with competent thymus.