Abstract
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.
Highlights
Pollution with trace metals is common in populated areas, and is mainly related to human-related activities (Tchounwou et al, 2012)
In order to gain a deeper understanding in how pollution with trace metals can affect the immune system of environmentally exposed wild small mammals, the present study investigated immunomodulatory ef fects of cadmium in wild ranging wood mice (Apodemus sylvaticus), environmentally exposed to known levels of cadmium
Individual cadmium concentrations in kidneys were significantly related to the mouse body mass (Fig. 1)
Summary
Pollution with trace metals is common in populated areas, and is mainly related to human-related activities (Tchounwou et al, 2012). The immune system can still be modulated by such low and chronic environmental exposures, potentially hampering protective host responses upon immune activation, for example during infections (Lehmann et al, 2011). Trace metals have been shown to modulate the immune system, lowering the resistance to infections in humans and animals (Heilmann, 2012; Krueger and Wade, 2016; Simonyte and Planciuniene, 2010). The modulated immune system of wild small mammals environmentally exposed to immunotoxic trace metals might not be able to limit infectious agents, thereby facilitating their trans mission, increasing the prevalence within the species and to other species, including humans (Bean et al, 2013; Mandl et al, 2015)
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