The Immune System in Antarctic and Subantarctic Fish of the Genus Harpagifer Is Affected by the Effects of Combined Microplastics and Thermal Increase

Rising ocean temperatures due to climate change, combined with the intensification of anthropogenic activity, may lead to changes in the physiology and distribution of native species. Compounding climate stress, microplastic particles (MPs) enter the oceans through wastewater and the breakdown of macroplastics. Depending on their composition, they can be harmful and act as a vehicle for toxic substances, although their effects on native Antarctic and subantarctic species are unknown. Notothenioid fish are members of this group and are found inside and outside Antarctica, such as the Harpagifer, which has adapted to the cold and is particularly sensitive to thermal increases. Here, we aimed to evaluate the innate immune response in the head kidney, spleen, and foregut of two notothenoid fish, <i>Harpagifer antarcticus</i> and <i>Harpagifer bispinis</i>, exposed to elevated temperatures and PVC (polyvinyl chloride) microplastics. Adults from both species were collected on King George Island (Antarctica) and Punta Arenas (Chile), respectively. Specimens were assigned to a control group or exposed to a temperature increase (TI) or PVC microplastics (MPs), separately or in combination (MPs + TI). MP exposures were oral (gavage) for 24 h or aqueous (in a bath) for 24 and 48 h. Using real-time qPCR, we evaluated the relative gene expression of markers involved in the innate immune response, including <i>tlr2</i> (<i>toll-like receptor 2</i>), <i>tlr4</i> (<i>toll-like receptor 4</i>), <i>myd88</i> (<i>myeloid differentiation factor 88</i>), <i>nfkb</i> (<i>nuclear factor kb</i>), <i>il6</i> (<i>interleukin 6</i>), and <i>il8</i> (<i>irterleukin 8</i>). We found differences between treatments when <i>H. antarcticus</i> and <i>H. bispinis</i> were exposed independently to MPs or thermal increase (TI) in the experiment with a cannula, showing an up-regulation in transcripts. In contrast, a down-regulation was observed when exposed in combination to MP + TI, which looked to be tissue-dependent. However, transcripts related to innate immunity in the bath experiment increased when exposure to both stressors was combined, mostly at 48 h. These results highlight the importance of evaluating the effects of multiple stressors, both independently and in combination, and whether these species will have the capacity to adapt or survive under these conditions, especially in waters where temperature is increasing and pollution is also rising, primarily from MP-PVC, a plastic widely used in various industries and among the population.