Cadmium (Cd) and lead (Pb) are known to enhance immune cell damages and to decrease cellular immunity, promoting higher susceptibility to infectious diseases. Selenium (Se) is an essential element involved in immunity and reactive oxygen species scavenging. This study aimed at evaluating how Cd and Pb and low nutritional (Se) quality modulate immune response to a bacterial lipopolysaccharide (LPS) challenge in wood mice (Apodemus sylvaticus). Mice were trapped near a former smelter in northern France in sites of High or Low contamination. Individuals were challenged immediately after capture or after five days of captivity, fed a standard or a Se-deficient diet. Immune response was measured with leukocyte count and plasma concentration of TNF-α, a pro-inflammatory cytokine. Faecal and plasma corticosterone (CORT), a stress-hormone involved in anti-inflammatory processes, was measured to assess potential endocrine mechanisms. Higher hepatic Se and lower faecal CORT were measured in free-ranging wood mice from High site. LPS-challenged individuals from High site showed steeper decrease of circulating leukocytes of all types, higher TNF-α concentrations, and a significant increase of CORT, compared to individuals from Low site. Challenged captive animals fed standard food exhibited similar patterns (decrease of leukocytes, increase of CORT, and detectable levels of TNF-α), with individuals from lowly contaminated site having higher immune responses than their counterparts from highly polluted site. Animals fed Se-deficient food exhibited lymphocytes decrease, no CORT variation, and average levels of TNF-α. These results suggest (i) a higher inflammatory response to immune challenge in free-ranging animals highly exposed to Cd and Pb, (ii) a faster recovery of inflammatory response in animals lowly exposed to pollution when fed standard food than more exposed individuals, and (iii) a functional role of Se in the inflammatory response. The role of Se and mechanisms underlying the relationship between glucocorticoid and cytokine remain to be elucidated.

The Wood mouse (Apodemus sylvaticus) is a widespread mammalian species that acts as a reservoir host for multiple infections, including zoonotic diseases. Exposure to immunotoxins, like for instance trace metals, may reduce the ability of the host to mount proper responses to pathogens, potentially increasing the transmission and prevalence of infections. Antibody-mediated responses are crucial in preventing and limiting infections, and the quantification of the primary antibody response is considered a sensitive predictor of immunosuppression. The current study aims to investigate effects of cadmium exposure on the antibody-mediated responses of wood mice inhabiting polluted and non-polluted areas in the Netherlands. Wood mice were captured alive at different locations and immunized to sheep red blood cells (SRBC) to induce a primary antibody response. SRBC-specific antibody-producing cells, or plaque forming cells (PFC), were quantified and related to kidney cadmium levels. Differential circulating main leukocyte populations were also characterised. Cadmium concentrations in mice kidneys differed between mice captured at different locations, and increased with individual body mass, likely associated with age-related time of exposure. Effect of cadmium was apparent on the percentages of B cell counts in blood. Because of potential natural immune heterogeneity between wild rodent populations, mice immune responses were analysed and compared grouped by captured locations. Capture location had significant effect on the total counts of white blood cells. Increasing cadmium exposure in wood mice captured from polluted sites was associated with a decrease of splenic PFC counts. This field research shows that wood mice antibody responses can be impaired by cadmium exposure, even at low environmental levels, by affecting B cell functioning mainly. Impaired B cell function can make exposed mice more susceptible to infections, potentially increasing the reservoir function of their populations. It also shows that immunomodulatory effects in the field should be assessed site specifically.

Risk assessment is needed for registration of each new phytopharmaceutical active substance at EU level. In France, the competent authority for registration is the Ministrer of Agriculture, taking into account opinions from "Commission des Toxiques" and "Comité d'Homologation". In regulatory risk assessment, environmental risk is estimated by the usual approach, combining exposure and hazard to calculate risk. Exposure is characterized by estimation of predicted environmental concentrations (PEC); hazard is estimated from ecotoxicological assays with different plant and/or animal species. Risk is characterized as a toxicity/exposure ratio, which is compared to a trigger value. This approach is simple, probably efficient, and could be scientifically improved. However, the system is not perfect, the main limitation being the variety of local environmental conditions. Furthermore, authorizations are based on specific products, and can not integrate a variety of agricultural practices. Biomonitoring is needed. | Depuis la Directive européenne 91/414, l'évaluation du risque environnemental est une obligation réglementaire pour toute nouvelle substance active phytopharmaceutique. En France, l'homologation dépend du Ministre de l'Agriculture, après avis de la Commission des Toxiques et du Comité d'Homologation. Le risque environnemental se détermine en combinant les 2 composantes du risque, danger et exposition. L'exposition se caractérise par le calcul des concentrations environnementales prévisibles dans l'environnement (PEC), et le danger par des données d'écotoxicité, déterminées à partir d'essais sur différentes espèces animales et végétales. Le risque est caractérisé par un rapport toxicité/exposition, comparé ensuite à une valeur-seuil. Le système est simple, probablement assez efficace, et peut être encore amélioré, en fonction des progrès scientifiques. Cependant, les limites de l'approche réglementaire sont connues, la principale étant la variété des situations environnementales. Enfin, les autorisations de mise sur le marché concernent des produits et ne peuvent intégrer la grande variété des pratiques agricoles. Une biosurveillance des milieux s'impose.