Effects of nano-and microplastics in the development of immune memory in the ascidian Ciona robusta

Microplastic contamination appears as one of the world's main environmental concerns. Small plastic fragments dispersed in the marine habitat can be consumed by different marine organisms and ultimately transferred to humans along the food chain. Microplastics could compromise the health of marine organisms by interfering with the functionality of the digestive system when ingested, but there is concern that they could also interact with the immune system and affect the susceptibility/resistance of animals to the infections. Recently, we have demonstrated the establishment of immune memory in the ascidian Ciona robusta by priming and challenging animals with microbial agents. This immune memory relies on the modulation of different cellular and humoral immune mechanisms, aiming to develop a more protective response. In the present study, we analyzed the expression level of several immune-related genes in pharynx and gut of animals primed by short- or long-term exposure (2 and 18 h) to nano- and micro-plastics (NMPs) and challenged seven days later with a prototypical inflammatory stimulus (bacterial lipopolysaccharide, LPS). We aimed to determine (i) whether the NMPs can induce an immune response in different tissues, (ii) whether the NMPs could prime the animals and drive the development of innate memory, and finally (iii) to which extent filter-feeding animals could stand this kind of pollutants. Transcription data suggest that animals primed with NMPs develop an immune memory that potentiates the secondary response to LPS and that such memory is tissue-specific and depends on both the length of the exposure period and the particle size. This study demonstrates that NMPs can modulate the immune reactivity of marine invertebrates, which can influence their defensive fitness. How this may affect their health and survival capacity is still unknown.