Effects on immunity of exposure to microplastics in adult zebrafish

It is now widely accepted that microplastics (MPs) represent a serious concern for aquatic environments, therefore assesment of biological pathways affected is crucially relevant. This study focused on variations of liver transcriptome, istology of gastrointestinal tract and gills, and locomotor activity of exposed fish along various days after treatment. Adult zebrafish (3 groups, N=12 each) were fed for 20 days with dry food alone (controls) or supplemented with a mix of pristine high-densitypolyethylene and polystyrene microplastics (0.1 or 1 mg/L), ranging in size from <25 to 90 μm. The exposure to MPs resulted in differential transcription of 324 genes in total, already affected at the lower dose, mainly involved in cholesterol biosynthesis (fatty acid degradation) and immunity pathways.Up-regulation of transcripts subserving response to extra-cellular antigens, and down-regulation of others involved in innate antimicrobial response, antiviral defense and maintenance of epithelial integrity highligted defective control of pathogen entry at epithelial barriers, confirmed by occurrence of histopathological signs in both intestine and gills. Furthermore, variations in energy utilization likely accounted also for alteration of circadian rhythm of locomotor activity.