Characterization of the zebrafish T cell receptor beta locus.

Zebrafish (Danio rerio) has become an increasingly important model for immunological study. Its immune system is remarkably similar to that of mammals and includes both the adaptive and innate branches. Zebrafish T cells express functional T cell receptors (TCR), and all four TCR loci are present within the genome. Using 5'-rapid amplification of cDNA ends, we cloned and sequenced zebrafish TCRbeta transcripts. TCRbeta VDJ coding joints demonstrate conservation of mechanisms used by other vertebrate species to increase junctional diversity. Using the sequences obtained, along with previously published data, we comprehensively annotated the zebrafish TCRbeta locus. Overall, organization of the locus resembles that seen in mammals. There are 51 V segments, a single D segment, 27 Jbeta1 segments, a single Jbeta2 segment, and two constant regions. This description of the zebrafish TCRbeta locus has the potential to enhance immunological research in zebrafish and further our understanding of mammalian TCR repertoire generation.

Necroinflammatory liver disease in BALB/c background, TGF-beta 1-deficient mice requires CD4+ T cells.

The etiology of autoimmune liver disease is poorly understood. BALB/c mice deficient in the immunoregulatory cytokine TGF-beta1 spontaneously develop necroinflammatory liver disease, but the immune basis for the development of this pathology has not been demonstrated. Here, we show that BALB/c-TGF-beta1(-/-) mice exhibit abnormal expansion in hepatic mononuclear cells (MNCs) compared with wild-type littermate control mice, particularly in the T cell and macrophage lineages. To test whether lymphocytes of the adaptive immune system are required for the spontaneous development of necroinflammatory liver disease, BALB/c-TGF-beta1(-/-) mice were rendered deficient in B and T cells by crossing them with BALB/c-recombinase-activating gene 1(-/-) mice. BALB/c-TGF-beta1(-/-)/recombinase-activating gene 1(-/-) double-knockout mice showed extended survival and did not develop necroinflammatory liver disease. The cytolytic activity of BALB/c-TGF-beta1(-/-) hepatic lymphocytes was assessed using an in vitro CTL assay. CTL activity was much higher in BALB/c-TGF-beta1(-/-) hepatic MNCs compared with littermate control hepatic MNCs and was particularly pronounced in the CD4(+) T cell subset. Experimental depletion of CD4(+) T cells in young BALB/c-TGF-beta1(-/-) mice prevented the subsequent development of necroinflammatory liver disease, indicating that CD4(+) T cells are essential for disease pathogenesis in vivo. These data definitively establish an immune-mediated etiology for necroinflammatory liver disease in BALB/c-TGF-beta1(-/-) mice and demonstrate the importance of CD4(+) T cells in disease pathogenesis in vivo. Furthermore, TGF-beta1 has a critical role in homeostatic regulation of the hepatic immune system, inhibiting the development or expansion of hepatic cytolytic CD4(+) T cells.