title: The development of cellular immune defence in marine medaka Oryzias melastigma.
abstract: Environmentally induced alterations of the immune system during sensitive developmental stages may manifest as abnormalities in immune organ configuration and/or immune cell differentiation. These not only render the early life stages more vulnerable to pathogens, but may also affect the adult immune competence. Knowledge of these sensitive periods in fish would provide an important prognostic/diagnostic tool for aquatic risk assessment of immunotoxicants. The marine medaka Oryzias melastigma is an emerging seawater fish model for immunotoxicology. Here, the presence and onset of four potentially sensitive periods during the development of innate and adaptive cellular immune defence were revealed in O. melastigma: 1.) initiation of phagocyte differentiation, 2.) migration and expansion of lymphoid progenitor cells, 3.) colonization of immune organs through lymphocyte progenitors and 4.) establishment of immune competence in the thymus. By using an established bacterial resistance assay for O. melastigma, larval immune competence (from newly hatched 1dph to 14dph) was found concomitantly increased with advanced thymus development and the presence of mature T-lymphocytes. A comparison between the marine O. melastigma and the freshwater counterpart Oryzias latipes disclosed a disparity in the T-lymphocyte maturation pattern, resulting in differences in the length of T-lymphocyte maturation. The results shed light on a potential difference between seawater and freshwater medaka in their sensitivity to environmental immunotoxicants. Further, medaka immune system development was compared and contrasted to economically important fish. The present study has provided a strong scientific basis for advanced investigation of critical windows for immune system development in fish.
authors.affiliation: State Key Laboratory in Marine Pollution, Department of Biology and Chemistry, City University of Hong Kong, Hong Kong Special Administrative Region.
authors.forename: Frauke
authors.initials: F
authors.lastname: Seemann
authors.affiliation: State Key Laboratory in Marine Pollution, Department of Biology and Chemistry, City University of Hong Kong, Hong Kong Special Administrative Region.
authors.forename: Drew Ryan
authors.initials: DR
authors.lastname: Peterson
authors.affiliation: State Key Laboratory in Marine Pollution, Department of Biology and Chemistry, City University of Hong Kong, Hong Kong Special Administrative Region.
authors.forename: Michael Wai Lun
authors.initials: MWL
authors.lastname: Chiang
authors.affiliation: State Key Laboratory in Marine Pollution, Department of Biology and Chemistry, City University of Hong Kong, Hong Kong Special Administrative Region. Electronic address: bhdwtau@cityu.edu.hk.
authors.forename: Doris Wai Ting
authors.initials: DWT
authors.lastname: Au
mesh_terms: D000818:Animals; D017756:Aquaculture; D058491:Bacterial Load; D002454:Cell Differentiation; D020609:Edwardsiella tarda / Q000254:growth & development / Q000276:immunology / Q000302:isolation & purification; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000276:immunology* / Q000382:microbiology; D047108:Embryonic Development; D018507:Gene Expression Regulation, Developmental; D060226:Head Kidney / Q000166:cytology / Q000254:growth & development / Q000276:immunology / Q000382:microbiology; D007111:Immunity, Cellular; D007113:Immunity, Innate; D007121:Immunocompetence; D017403:In Situ Hybridization / Q000662:veterinary; D007814:Larva / Q000166:cytology / Q000254:growth & development / Q000276:immunology* / Q000382:microbiology; D054503:Lymphoid Progenitor Cells / Q000166:cytology / Q000276:immunology / Q000382:microbiology; D009024:Morphogenesis; D009990:Oryzias / Q000196:embryology / Q000254:growth & development / Q000276:immunology* / Q000382:microbiology; D010586:Phagocytes / Q000166:cytology / Q000276:immunology / Q000382:microbiology; D013045:Species Specificity; D013154:Spleen / Q000166:cytology / Q000254:growth & development / Q000276:immunology / Q000382:microbiology; D016019:Survival Analysis; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000382:microbiology; D013950:Thymus Gland / Q000166:cytology / Q000254:growth & development / Q000276:immunology / Q000382:microbiology
keywords: Aquatic risk assessment; Head kidney; Immunotoxicity; Lymphocytes; Phagocytes; Thymus