Microplastics predominantly accumulate in CD11b⁻ macrophages of the liver and spleen without overt neutrophil activation

To estimate the health effects of internal microplastics exposure, it is crucial to understand their dynamics and the effects on immune cells. To confirm that microplastics are transported from the intestinal lumen to the bloodstream, we fed mice 1 µm polystyrene (PS) spheres and analyzed the blood, mesenteric lymph node, spleen and liver. We found limited amounts of microplastics back in the draining lymph node only. To simulate the distribution of microplastics from human blood to distant organs, 1 µm PS microplastics were injected intravenously to identify accumulation points of microplastics in the body and to understand the response of the immune system. The plastics accumulated mostly in liver and spleen which are blood filtering organs. Phagocytes involved in filtering these microplastics in liver and spleen were mainly CD11b- macrophage populations. Neutrophils phagocytosed the second most microplastics, but showed only limited recruitment and activation. Our study shows microplastics accumulate in liver and spleen and that CD11b- macrophages are the predominant phagocyte involved.