The immune system of zebrafish : Development, maturation and effect of thyroid hormones

Abstract

The zebrafish offers an attractive complimentary model to the mouse for immunological research. The present study is aimed at providing insights into the transformation of the zebrafish immune system from an immature to a mature state, to further establish zebrafish as an immunological model. The zebrafish thymus is morphologically mature by 3 weeks post-fertilization (wpf). By 6 wpf, the expression levels of immune-related genes such as Rag-1, TCRAC and IgLC isotypes were observed to resemble that of a mature immune system of the adult fish. The present study also demonstrated that cell-mediated immunity in zebrafish was already functioning between 3-4 wpf. The onset of secreted immunoglobulin was detected by 4 wpf. Humoral response to T-independent antigen and T-dependent antigen were observed in zebrafish immunized at 4 and 6 wpf, respectively. The findings revealed that the zebrafish immune system is morphologically and functionally mature by 4-6 wpf. Thymus development and thymopoiesis was affected by T4 and MMI-treatments. A thyroid hormone and immune system relationship was shown to be likely conserved from fish to higher vertebrates.