The contamination of ecosystem compartments by microplastics (MPs) is an ubiquitous problem. MPs have been observed in mice tissues, and recently in human blood, stool and placenta. However, two aspects remain unclear: whether MPs accumulate in peripheral organs, specifically in the liver, and if liver cirrhosis favours this process. We aimed to examine human liver tissue samples to determine whether MPs accumulate in the liver. This proof-of-concept case series, conducted in Germany, Europe, analyzed tissue samples of 6 patients with liver cirrhosis and 5 individuals without underlying liver disease. A total of 17 samples (11 liver, 3 kidney and 3 spleen samples) were analyzed according to the final protocol. A reliable method for detection of MP particles from 4 to 30 µm in human tissue was developed. Chemical digestion of tissue samples, staining with Nile red, subsequent fluorescent microscopy and Raman spectroscopy were performed. Morphology, size and composition of MP polymers were assessed. Considering the limit of detection, all liver, kidney and spleen samples from patients without underlying liver disease tested negative for MPs. In contrast, MP concentrations in cirrhotic liver tissues tested positive and showed significantly higher concentrations compared to liver samples of individuals without underlying liver disease. Six different microplastic polymers ranging from 4 to 30 µm in size were detected. This proof-of-concept case series assessed the presence of MPs in human liver tissue and found six different MP polymers in the liver of individuals with liver cirrhosis, but not in those without underlying liver disease. Future studies are needed to evaluate whether hepatic MP accumulation represents a potential cause in the pathogenesis of fibrosis, or a consequence of cirrhosis and portal hypertension. No funding was received for conducting this investigator driven study.

IL-22 is one of the factors that, although important for wound healing, also promote tumorigenesis; the regulation of IL-22BP, the IL-22 binding protein, via the NLRP3 and NLRP6 inflammasomes provides an unanticipated mechanism, controlling IL-22 and thereby the development of colon cancer. IL-22-binding protein (IL-22BP) is a soluble receptor that specifically binds to and neutralizes the cytokine interleukin (IL) 22, but its physiological function in vivo is unknown. Using a new IL-22BP-knockout mouse strain, this study shows that IL-22BP is required for epithelial tissue repair in a mouse model of colitis and to prevent the development of colon cancer owing to unrestrained IL-22-mediated epithelial proliferation. IL-22BP is downregulated by an inflammasome- and IL-18-dependent mechanism after initial tissue damage to allow for repair. Chronic mucosal inflammation and tissue damage predisposes patients to the development of colorectal cancer1. This association could be explained by the hypothesis that the same factors and pathways important for wound healing also promote tumorigenesis. A sensor of tissue damage should induce these factors to promote tissue repair and regulate their action to prevent development of cancer. Interleukin 22 (IL-22), a cytokine of the IL-10 superfamily, has an important role in colonic epithelial cell repair, and its levels are increased in the blood and intestine of inflammatory bowel disease patients2,3. This cytokine can be neutralized by the soluble IL-22 receptor, known as the IL-22 binding protein (IL-22BP, also known as IL22RA2); however, the significance of endogenous IL-22BP in vivo and the pathways that regulate this receptor are unknown4,5. Here we describe that IL-22BP has a crucial role in controlling tumorigenesis and epithelial cell proliferation in the colon. IL-22BP is highly expressed by dendritic cells in the colon in steady-state conditions. Sensing of intestinal tissue damage via the NLRP3 or NLRP6 inflammasomes led to an IL-18-dependent downregulation of IL-22BP, thereby increasing the ratio of IL-22/IL-22BP. IL-22, which is induced during intestinal tissue damage, exerted protective properties during the peak of damage, but promoted tumour development if uncontrolled during the recovery phase. Thus, the IL-22–IL-22BP axis critically regulates intestinal tissue repair and tumorigenesis in the colon.

Interleukin-17-producing T helper (TH17) cells serve an important role in the immune system, but are strongly implicated in the pathogenesis of numerous autoimmune diseases including rheumatoid arthritis and multiple sclerosis. How the immune system controls TH17 cells in vivo remains unclear. Using mice in which tolerance was induced by CD3-specific antibody, a model of sepsis and influenza A viral infection, Esplugues et al. demonstrate that TH17 cells are kept in check by redirecting the cells to the small intestine where they are eliminated or re-programmed to acquire immunosuppressive and regulatory properties. This work identifies the gastrointestinal tract as a site for control of TH17 cells. Interleukin (IL)-17-producing T helper cells (TH17) are a recently identified CD4+ T cell subset distinct from T helper type 1 (TH1) and T helper type 2 (TH2) cells1. TH17 cells can drive antigen-specific autoimmune diseases and are considered the main population of pathogenic T cells driving experimental autoimmune encephalomyelitis (EAE)2, the mouse model for multiple sclerosis. The factors that are needed for the generation of TH17 cells have been well characterized3,4,5,6. However, where and how the immune system controls TH17 cells in vivo remains unclear. Here, by using a model of tolerance induced by CD3-specific antibody, a model of sepsis and influenza A viral infection (H1N1), we show that pro-inflammatory TH17 cells can be redirected to and controlled in the small intestine. TH17-specific IL-17A secretion induced expression of the chemokine CCL20 in the small intestine, facilitating the migration of these cells specifically to the small intestine via the CCR6/CCL20 axis. Moreover, we found that TH17 cells are controlled by two different mechanisms in the small intestine: first, they are eliminated via the intestinal lumen; second, pro-inflammatory TH17 cells simultaneously acquire a regulatory phenotype with in vitro and in vivo immune-suppressive properties (rTH17). These results identify mechanisms limiting TH17 cell pathogenicity and implicate the gastrointestinal tract as a site for control of TH17 cells.