Exploring the Internal Defense System of Cerastoderma glaucum (Bruguière, 1789) Exposed to Pristine Microplastics: The Sentinel Role of Haemocytes as Biomarkers

The ubiquitous presence of microplastics (MPs) in the environment is a major concern for the conservation of biodiversity. Numerous studies show the detrimental effects of MPs on marine species, especially because of their small size and their capacity to absorb organic contaminants from their surroundings. The bivalve mollusk Cerastoderma glaucum (Bruguière, 1789), because of its wide geographic distribution and immobile feeding habits, can be used as a sentinel and bioindicator species. By examining the presence, localization, and co-localization of Toll-like receptor 2 (TLR2) and inducible nitric oxide synthetase (iNOS), this study aims to evaluate the response of the internal defense system of C. glaucum to pristine MPs through the employment of confocal microscopy and bioinformatics techniques. The results show haemocytes immunoreactive to the antibodies tested; in particular, a higher number of TLR2-positive haemocytes can be observed in the group exposed to pristine MPs. These findings suggest that haemocytes can play a key biomarker role as sentinels to environmental pollutants. Furthermore, bioinformatics analyses on the antibodies tested confirmed an evolutionary conservation of these molecules. These data highlight the critical role of phagocytosis in identifying ecosystem damage and are helpful in developing biosensors with less negative effects on the environments in which they are applied.