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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.

The effect of previous toxicant exposure (i.e., exposure history) on an organism's response to re-exposure to the toxicant is of considerable interest. The marine mussel Mytilus edulis was collected from reference and polluted sites in southwest England, and groups of mussels from each site were exposed to 20 μg/L CdCl2 for 0, 1, 4, and 8 days and compared with unexposed controls. End points evaluated were tissue metal and electrolyte concentrations, haemolymph chemistry, haemocyte characteristics [counts, neutral red uptake (NRU), and phagocytosis], histology, and expression of metallothionein gene (mt10) expression in digestive glands. Field-collected animals differed by collection site for some end points at time zero, at which time tissue Fe and Pb concentrations were greater and NRU and condition index lower in mussels from the polluted site. Subsequent exposure to cadmium (Cd) in the laboratory caused Cd accumulation mainly in digestive gland, but there were no site-specific effects on tissue trace-metal concentrations. NRU, phagocytosis, and haemolymph Na(+) and K(+) concentrations differed among sites and Cd treatment, but there were no clear trends. Exposure to Cd resulted in lower Ca(2+) concentrations in gill, digestive gland, and haemolymph in animals from the polluted site compared with controls (Kruskal-Wallis, p ≤ 0.05). Lesions, including necrosis, inflammation, and neoplasia, were observed in animals from the polluted site, but the frequency of these lesions appeared to decrease unexpectedly after Cd exposure. Expression of mt10 increased 3-fold in Cd-exposed animals from the polluted site compared with all other groups (Kruskal-Wallis, p = 0.01). We conclude that Cd exposure affected some immune responses in M. edulis, but pre-exposure history influenced toxicological outcomes of Cd exposure in the laboratory.

Artemia franciscana is a native species to the New World, and became an exotic species to most parts of the world. The Egyptian hypersaline, continental Qaroun Lake (Fayoum Governorate, Middle of Egypt) is subjected to a gradually increasing salinity rates that approximate or exceed these of seawater. Artemia populations there are known to be parthenogenetic. Yet, these populations started to exhibit abnormal morphologies. Therefore, Qaroun Lake samples of Artemia were subjected to several morphological, biometric, and molecular phylogenetic analyses for accurate species identification and phylogeographic origin approximation. These analyses revealed the existence of the alien sexual species of brine shrimp A. franciscana in Qaroun Lake. The characteristics of the subspherical frontal knob with several spines on the top, ovisac lateral triangular lobe on both sides and its projection together with the biometrics confirmed this species morphotype. DNA barcoding and other molecular analyses based on PCR-based amplification and sequencing of the barcode region of the cytochrome oxidase subunit I gene (COI) exhibited that all the collected samples belong to five haplotypes. Egyptian A. franciscana COI sequences phylogeny and pairwise distances analysis exhibited closer proximity to Latin American strains than to the Northern American ones. A. franciscana presence may be ascribed to the migratory birds present in Qaroun Lake protectorate, since no marine aquaculture activity in Qaroun Lake is known. Therefore, and for the best of our knowledge, this is the first record of the invasive A. franciscana in Egypt.