Characterizing the Immune Function of the Brown Bullhead (Ameiurus nebulosus) from Less Contaminated and Highly Contaminated Locations along the Detroit River

Abstract

Some fish populations are able to adapt and thrive in contaminated habitats. Survival of populations depends on the ability of the organism to elicit resistance, either due to genetic adaptation or physiological acclimations. Brown Bullheads (Ameiurus nebulosus) are able to survive in very contaminated areas and their benthic and philopatric characteristics make them a model organism to study chronic exposure. This research assesses the immune function of brown bullhead collected at four pre-determined sites along the Detroit River, which are characterized by high or low concentrations of environmental toxicants. Clean and contaminated sediment used for contaminant exposure was collected by ponar at designated sites of the river. The bullheads were vaccinated with heat-killed V. anguillarum in order to induce an immune response, before the vaccinated bullheads were randomly divided into corresponding contaminant exposure tanks. Respiratory burst assays to assess innate oxygen radical production 24hrs post vaccination and sediment exposure identified an inhibition of neutrophil oxidative activity in adult 6 month cleared of contaminant bullheads collected from a clean (Peche Island) site exposed to contaminated sediment, and of F1 raised populations from a contaminated (Trenton Channel) site. Results also showed overall inhibition on contaminated sediment in both PI and TC recently captured fish. Enzyme linked immunosorbant assay (ELISA) to assess antibody production revealed no difference between those fish exposed to either sediment. Results did show a lower expression of total antibody in chronically contaminant exposed bullheads (acute adults). Real time PCR to assess immune gene expression was conducted using cloned Major Histocompatibility Class II Beta (MHIIB), Interleukin-8 (IL-8) and Interleukin-1 Beta (IL-1B) 24hr post vaccination and sediment exposure. No contaminant induced immunosuppression of MHIIB was observed, while a reduction in IL-8 and IL-1B in acute adults may signify a delayed response due to chronic sediment exposure or of a normal functioning delayed response in wild bullheads. Results of the present study indicate negative environmental impacts on the innate immune response, leading to physiological adaptations in the brown bullhead, which can be reversed upon removal of the contaminants.