Immunological Responses of Marine Bivalves to Contaminant Exposure: Contribution of the -Omics Approach

Abstract

The increasing number of data studies on the biological impact of anthropogenic chemicals in the marine environment, together with the great development of invertebrate immunology, has identified marine bivalves as a key invertebrate group for studies on immunological responses to pollutant exposure. Available data on the effects of contaminants on bivalve immunity, evaluated with different functional and molecular endpoints, underline that individual functional parameters (cellular or humoral) and the expression of selected immune-related genes can distinctly react to different chemicals depending on the conditions of exposure. Therefore, the measurement of a suite of immune biomarkers in hemocytes and hemolymph is needed for the correct evaluation of the overall impact of contaminant exposure on the organism's immunocompetence. Recent advances in -omics technologies are revealing the complexity of the molecular players in the immune response of different bivalve species. Although different -omics represent extremely powerful tools in understanding the impact of pollutants on a key physiological function such as immune defense, the -omics approach has only been utilized in this area of investigation in the last few years. In this work, available information obtained from the application of -omics to evaluate the effects of pollutants on bivalve immunity is summarized. The data shows that the overall knowledge on this subject is still quite limited and that to understand the environmental relevance of any change in immune homeostasis induced by exposure to contaminants, a combination of both functional assays and cutting-edge technology (transcriptomics, proteomics, and metabolomics) is required. In addition, the utilization of metagenomics may explain how the complex interplay between the immune system of bivalves and its associated bacterial communities can be modulated by pollutants, and how this may in turn affect homeostatic processes of the host, host-pathogen interactions, and the increased susceptibility to disease. Integrating different approaches will contribute to knowledge on the mechanism responsible for immune dysfunction induced by pollutants in ecologically and economically relevant bivalve species and further explain their sensitivity to multiple stressors, thus resulting in health or disease.

Keywords: -omics technologies; biomarkers; bivalves; environmental stress; immunity; pollutants.

Figure 1

Schematic overview showing the integration of different -omics approaches in evaluating the impact of pollutants on the immune responses of bivalves and their consequences on organism health. Left: The effects of different contaminants (heavy metals, organic xenobiotics, and nanoparticles) can be evaluated on the main components of the immune system, hemocytes, and hemolymph plasma, determining functional immune responses as classical immune biomarkers. The application of metagenomics to hemolymph samples can provide an estimation of how contaminant exposure may shape the interactions between innate immune defenses and the associated microbial communities. Right: Different -omics tools approaches applied to both hemocytes and tissues can reveal perturbations of immune responses as changes in gene and protein expression networks and metabolic profiles related to immune processes at cellular and tissue level and can identify immune targets for different classes of pollutants. The overall information will help understanding how contaminant exposure can affect the capacity of different bivalves to cope with pathogen challenge, thus increasing their susceptibility to disease, with possible consequences on the health status of natural populations and aquacultured species.