Tissue Injury and Cellular Immune Responses to Cadmium Chloride Exposure in the Common Mussel Mytilus edulis: Modulation by Lipopolysaccharide

Abstract

The immunotoxic effects of cadmium (Cd) exposure in bivalves are poorly understood and whether or not stimulation of the immune system exacerbates Cd toxicity is unclear. The mussel Mytilus edulis was exposed to 20 or 50 μg/l total Cd for up to 11 days compared to no added Cd controls to assess immune and other physiological responses. Selected experiments were then repeated in the presence of a lipopolysaccharide (LPS) challenge with and without subsequent Cd exposure. Immune functions of hemocytes, hematology, hemolymph glucose and ion content, as well as superoxide dismutase (SOD) activity and organ pathology were measured. Cd accumulated mainly in digestive gland and gills and to a lesser extent in the adductor muscle. Exposure to 20 μg/l Cd alone caused a transient modulated of phagocytosis and increased neutral red retention (Kruskal-Wallis, p = 0.002). The higher Cd concentration also increased cytotoxicity, and decreased hemocyte count. Changes in hemolymph Na(+), K(+), and glucose were small or negligible. Histopathological examination showed tissue injuries consistent with inflammation and necrosis in the gills, digestive gland, and adductor muscle during Cd exposure alone. LPS injection alone and LPS + Cd caused an increase in the number of circulating hemocytes by the end of the experiment (Kruskal-Wallis, p = 0.01) and a transient rise in phagocytosis at day 4 (analysis of variance (ANOVA), p = 0.001). The LPS + Cd treatment also caused transient changes in neutral red retention and in the cytotoxicity of hemocytes compared to controls. Intracellular SOD activity did not change in hemocytes under any treatment. Tissue inflammation and pathology was greatly increased by the effect of Cd exposure with an LPS injection compared to either treatment alone. We conclude that immunostimulation with LPS can greatly increase Cd-related organ pathologies but does not necessarily alter the responses of hemocytes.

An integrated proteomic and metabolomic study on the gender-specific responses of mussels Mytilus galloprovincialis to tetrabromobisphenol A (TBBPA)

“…In this study, gills presented loss of frontal cilia and lateral cilia after TBBPA treatment for 30 days, which suggested that TBBPA might affect the normal respiration and nutrient uptake. Similar phenomena have been reported in mussels exposed to tri-n-butyltin, Cd and mussels from natural polluted environments polluted by various heavy metals (Micic et al, 2001;Sheir and Handy, 2010;Fasulo et al, 2008). Due to a lack of adaptive immunity in mussels, the hemocytes are very important for immune defense, and the circulating hemocytes are able to penetrate tissue in response to antigens.…”

“…Histological sections (6-8 μm thickness) were stained with hematoxylin-eosine (HE) and observed under a light microscope (Olympus BX61, Tokyo, Japan) at × 200 magnification (zoom on the camera was × 2.5). The injury of mussel gills was measured according to previous study with some modifications (Sheir and Handy, 2010). The detailed information on making sections and histological observations were described in the Supporting Information.…”

Effects of environmental hypercapnia and metal (Cd and Cu) exposure on acid-base and metal homeostasis of marine bivalves

“…This mechanism can explain the stimulation of caspase-independent apoptosis in molluscan hemocytes by Cd (Sokolova et al, 2004) and may contribute to Cd-induced immunosuppression (Butler and Roesijadi, 2000;Sheir and Handy, 2010;Bruneau et al, 2013;Ivanina et al, 2014).…”

Oral immunostimulation of the oyster Ostrea edulis: Impacts on the parasite Bonamia ostreae

“…LPS and zymosan (Sigma) at a concentration of 300 mg/g wet weight were selected for the assay based on previous studies [52,53]. A total of 13 oysters were held in 10 L tanks with aeration.…”