Effects of arsenic on zebrafish innate immune system.

The innate immune response, the first line of defense against invading pathogens, can be perturbed by environmental toxicants such as arsenic. This study reports the effects of arsenic on innate immunity of zebrafish. Respiratory burst activity, messenger RNA expression of tumor necrosis factor alpha (TNF-alpha), a primer of the respiratory burst response, and mRNA expression of the antiviral cytokines interferon (IFN) and MX, : before and after viral infection, were examined in arsenic-exposed zebrafish larvae. Respiratory burst activity and TNF-alpha expression were decreased upon arsenic exposure, indicating inhibition of TNF-alpha priming of the respiratory burst response. Arsenic enhanced IFN expression slightly over time, but reduced MX : expression. In zebrafish infected with snakehead rhabdovirus, arsenic decreased induction and altered the kinetics of IFN and MX : upon infection. Differences in IFN and MX : expression in arsenic-exposed larvae point toward an interruption of the Janus kinase-signal transducer and activator of transcription (JAK/STAT) pathway.

Development of a respiratory burst assay using zebrafish kidneys and embryos.

The innate immune response constitutes the first line of defense against invading pathogens and consists of a variety of immune defense mechanisms including the respiratory burst of phagocytes. Respiratory burst can be used as a reliable measure of the immune response of a host, and numerous assays have been developed to measure this response in a variety of mammal and fish species. Phagocytes, like granulocytes and macrophages, that are derived from different tissues, or grown in cell culture, have been employed in a range of assay formats employing a variety of detection methods. The small size of the zebrafish has prevented the large-scale extraction of these cells for respiratory burst assays in the zebrafish. In this work, we describe a respiratory burst assay developed for the zebrafish using intact kidneys and embryos as sources of phagocytes. Phorbol myristate acetate (PMA)-inducible reactive oxygen species (ROS) were detected following the oxidation of a non-fluorescent dye 2',7'-dihydrodichlorofluorescein diacetate (H2DCFDA) to dichlorofluorescein (DCF), a fluorescent product. Embryos from 1 day post-fertilization until 5 days post-fertilization (dpf) were employed in this assay. Abrogation of H2DCFDA oxidation by the protein kinase C (PKC) inhibitor bisindolylmaleimide I (BisI) indicated a reduction in the respiratory burst. Fluorescence from the PMA-induced respiratory burst in kidneys and embryos was significantly elevated above DMSO-treated controls, while preincubation with BisI inhibited the increase in fluorescence. Colocalization of cell-associated chloromethyl-dihydrodichlorofluorescein diacetate (CM-H2DCFDA) with the phagocyte-selective dye neutral red is consistent with the observation that macrophages and granulocytes are the ROS-producing cells in the zebrafish.

LMP1 signaling can replace CD40 signaling in B cells in vivo and has unique features of inducing class-switch recombination to IgG1.

The Epstein-Barr virus (EBV) protein LMP1 is considered to be a functional homologue of the CD40 receptor. However, in contrast to the latter, LMP1 is a constitutively active signaling molecule. To compare B cell-specific LMP1 and CD40 signaling in an unambiguous manner, we generated transgenic mice conditionally expressing a CD40/LMP1 fusion protein, which retained the LMP1 cytoplasmic tail but has lost the constitutive activity of LMP1 and needs to be activated by the CD40 ligand. We show that LMP1 signaling can completely substitute CD40 signaling in B cells, leading to normal B-cell development, activation, and immune responses including class-switch recombination, germinal center formation, and somatic hypermutation. In addition, the LMP1-signaling domain has a unique property in that it can induce class-switch recombination to IgG1 independent of cytokines. Thus, our data indicate that LMP1 has evolved to imitate T-helper cell function allowing activation, proliferation, and differentiation of EBV-infected B cells independent of T cells.