Immune response and disease resistance of Oreochromis mossambicus to Aeromonas hydrophila after exposure to hexavalent chromium

Abstract

The objective of this study was to investigate the effect of chronic exposure to sublethal concentrations of hexavalent chromium (K 2 Cr 2 O 7 ) on the immune response and disease resistance of Oreochromis mossambicus (Peters) to bacterial Aeromonas hydrophila infection. Fish (45 to 50 g) were exposed to 0.005, 0.05, 0.5, and 5 mg l -1 [0.01, 0.1, 1, and 10% LC 50 , respectively] of hexavalent chromium Cr (VI) for 28 d. The specific immune response was assessed by antibody response to A. hydrophila by bacterial agglutination assay, and to sheep red blood cells (SRBC) by plaque forming cell (PFC) assay. In addition, nonspecific immune mechanisms were assessed by serum lysozyme activity and reactive nitrogen intermediates, the latter in terms of nitric oxide (NO) production by peripheral blood leucocytes. Overall immunity was assessed by disease resistance against live virulent A. hydrophila. The study clearly indicated that chronic exposure of fish to 0.5 and 5 mg l -1 of chromium (VI) decreased both nonspecific and specific parameters of the immune system, which resulted in a lower disease resistance to A. hydrophila. Interestingly, 0.05 mg l -1 of Cr (VI) enhanced disease resistance and both nonspecific and specific immune responses to A. hydrophila. Our study revealed a concentration-dependent modulation of the immune system by chromium (VI), as demonstrated by suppressive or stimulatory effects on lymphocytes, lysozyme, phagocytic killing mechanisms, and disease resistance in O. mossambicus.

Immunomodulation in Mytilus galloprovincialis by non-toxic doses of hexavalent Chromium

“…In both conditions, decreases in lysozyme activity and phagocytosis, together with increases in radical production, suggest an impairment of immunocompetence associated with inflammatory processes. In vivo, these responses were observed at Cr(VI) concentrations lower than those previously utilized in studies with freshwater fish [11,12]. In addition to functional responses, the results of this work represent the first data on the in vivo effects of Cr(VI) on gene expression in bivalve replicates for each sample, and are expressed as percent values obtained in control and metal-exposed mussels.…”

“…In the rainbow trout, Onchorhynchus mykiss, exposure to different heavy metals was shown to affect immune parameters, including lysozyme activity and phagocytosis [35]. Chronic exposure of O. mossambicus to Cr(VI) increased or decreased serum lysozyme activity at low and high concentrations, respectively [12]. The Crinduced decrease in lysozyme activity observed in this work may be due to either reduced release by the hemocytes associated with reduced phagocytic activity, or inhibition of enzyme activity.…”

“…In fact, there is evidence that in vitro exposure of carp leukocytes to micromolar concentrations of hexavalent Cr(VI) could lead to cytotoxic effects, as well as to decreased mitogen-induced lymphocyte activation and phagocyte function [11]. In the African mouthbreeder Oreochromis mossambicus, chronic exposure to sub-lethal concentrations of Cr(VI) exerted both stimulatory or suppressive effects on lymphocytes, lysozyme, phagocytic killing mechanisms and disease resistance, at lower and higher concentrations, respectively [12]. Due to the widespread use of Cr in industry and the prevalence of Cr contamination in aquatic habitats, there is a need for immunotoxicological data in order to assess the potential health risks associated with exposure to this metal for different aquatic vertebrate and invertebrate species.…”

Enhancement of nonspecific immunity and disease resistance in Oreochromis mossambicus by Solanum trilobatum leaf fractions

“…Water was changed on alternate days. Fish were acclimated for a period of 2 weeks and fed ad libitum with a balanced fish diet prepared in the laboratory [30].…”

Immunotoxicological Effects of Environmental Contaminants in Teleost Fish Reared for Aquaculture

“…Thus, tilapia (Oreochromis mossambicus) specimens exposed to sublethal doses of Cr-containing tannery effluents suffered a decreased antibody production, serum lysozyme activity and production of ROS and RNI by peripheral blood leucocytes (Sudhan & Michael, 1995;Prabakaran et al, 2007). Tilapia specimens exposed for 28 days with 0.5 and 5 mg Cr (VI)/L also decreased the disease resistance to bacterial infection and non-specific and specific immune response whilst the exposure with 0.05 mg Cr (VI)/L produced the opposite effects (Prabakaran et al, 2006). In another study, the spleen weight and the lymphocyte and leucocyte counts were significantly reduced by chronic exposure to Cr (III) and Cr (VI), producing the hexavalent form the greatest inhibitions (Arunkumar et al, 2000).…”