title: Chronic exposure to low concentration of arsenic is immunotoxic to fish: role of head kidney macrophages as biomarkers of arsenic toxicity to Clarias batrachus.
abstract: The present study was aimed at elucidating the effect of chronic low-level arsenic exposure on the head kidney (HK) of Clarias batrachus and at determining the changes in head kidney macrophage (HKM) activity in response to arsenic exposure. Chronic exposure (30 days) to arsenic (As(2)O(3), 0.50 microM) led to significant increase in arsenic content in the HK accompanied by reduction in both HKM number and head kidney somatic index (HKSI). Arsenic induced HK hypertrophy, reduction in melano-macrophage population and increased hemosiderin accumulation. Transmission electron microscopy of 30 days exposed HKM revealed prominent endoplasmic reticulum, chromatin condensation and loss in structural integrity of nuclear membrane. Head kidney macrophages from exposed fish demonstrated significant levels of superoxide anions but on infection with Aeromonas hydrophila were unable to clear the intracellular bacteria and died. Exposure-challenge experiments with A. hydrophila revealed that chronic exposure to micromolar concentration of arsenic interfered with the phagocytic potential of HKM, helped in intracellular survival of the ingested bacteria inside the HKM inducing significant HKM cytotoxicity. The immunosuppressive effect of arsenic was further evident from the ability of A. hydrophila to colonize and disseminate efficiently in exposed fish. Enzyme linked immunosorbent assay indicated that chronic exposure to arsenic suppressed the production of pro-inflammatory 'IL-1beta like' factors from HKM. It is concluded that arsenic even at very low concentration is immunotoxic to fish and the changes observed in HKM may provide a useful early biomarker of low-level xenobiotic exposure.
authors.affiliation: Immunobiology Laboratory, School of Life Sciences, Visva Bharati University, Santiniketan 731 235, India.
authors.forename: Soma
authors.initials: S
authors.lastname: Datta
authors.forename: Debabrata
authors.initials: D
authors.lastname: Ghosh
authors.forename: Dhira Rani
authors.initials: DR
authors.lastname: Saha
authors.forename: Shelley
authors.initials: S
authors.lastname: Bhattacharaya
authors.forename: Shibnath
authors.initials: S
authors.lastname: Mazumder
mesh_terms: D016980:Aeromonas hydrophila / Q000254:growth & development; D000818:Animals; D001151:Arsenic / Q000633:toxicity*; D015415:Biomarkers / Q000032:analysis; D002397:Catfishes / Q000254:growth & development / Q000276:immunology* / Q000382:microbiology; D004305:Dose-Response Relationship, Drug; D053583:Interleukin-1beta / Q000276:immunology; D007668:Kidney / Q000187:drug effects* / Q000276:immunology / Q000382:microbiology / Q000648:ultrastructure; D008264:Macrophages / Q000187:drug effects* / Q000276:immunology / Q000382:microbiology / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D010587:Phagocytosis / Q000187:drug effects* / Q000276:immunology; D017382:Reactive Oxygen Species / Q000378:metabolism; D013054:Spectrophotometry, Atomic; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D015415:Biomarkers; D053583:Interleukin-1beta; D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical; D001151:Arsenic