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Endoscopic photoconversion reveals unexpectedly broad leukocyte trafficking to and from the gut.

ABSTRACT: Given mounting evidence of the importance of gut-microbiota/immune-cell interactions in immune homeostasis and responsiveness, surprisingly little is known about leukocyte movements to, and especially from, the gut. We address this topic in a minimally perturbant manner using Kaede transgenic mice, which universally express a photoconvertible fluorescent reporter. Transcutaneous exposure of the cervical lymph nodes to violet light permitted punctual tagging of immune cells specifically therein, and subsequent monitoring of their immigration to the intestine; endoscopic flashing of the descending colon allowed specific labeling of intestinal leukocytes and tracking of their emigration. Our data reveal an unexpectedly broad movement of leukocyte subsets to and from the gut at steady state, encompassing all lymphoid and myeloid populations examined. Nonetheless, different subsets showed different trafficking proclivities (e.g., regulatory T cells were more restrained than conventional T cells in their exodus from the cervical lymph nodes). The novel endoscopic approach enabled us to evidence gut-derived Th17 cells in the spleens of K/BxN mice at the onset of their genetically determined arthritis, thereby furnishing a critical mechanistic link between the intestinal microbiota, namely segmented filamentous bacteria, and an extraintestinal autoinflammatory disease.

SUBMITTER: Morton AM

PROVIDER: S-EPMC4020091 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Perinatal infection and inflammation are major risk factors for injury in the developing brain, however, underlying mechanisms are not fully understood. Leukocyte migration to the cerebrospinal fluid (CSF) and brain is a hallmark of many pathologies of the central nervous system including those in neonates. We previously reported that systemic activation of Toll-like receptor (TLR) 2, a major receptor for gram-positive bacteria, by agonist Pam3CSK4 (P3C) resulted in dramatic neutrophil and monocyte infiltration to the CSF and periventricular brain of neonatal mice, an effect that was absent by the TLR4 agonist, LPS. Here we first report that choroid plexus is a route of TLR2-mediated leukocyte infiltration to the CSF by performing flow cytometry and transmission electron microscopy (TEM) of the choroid plexus. Next, we exploited the striking discrepancy between P3C and LPS effects on cell migration to determine the pathways regulating leukocyte trafficking through the choroid plexus. We performed RNA sequencing on the choroid plexus after administration of P3C and LPS to postnatal day 8 mice. A cluster gene analysis revealed a TLR2-specific signature of chemotaxis represented by 80-fold increased expression of the gene Ccl3 and 1000-fold increased expression of the gene Cxcl2. Ingenuity pathway analysis (IPA) revealed TLR2-specific molecular signaling related to cytoskeleton organization (e.g. actin signaling) as well as inositol phospholipids biosynthesis and degradation. This included upregulation of genes such as Rac2 and Micall2. In support of IPA results, ultrastructural analysis by TEM revealed clefting and perforations in the basement membrane of the choroid plexus epithelial cells in P3C-treated mice. In summary, we show that the choroid plexus is a route of TLR2-mediated transmigration of neutrophils and monocytes to the developing brain, and reveal previously unrecognized mechanisms that includes a specific chemotaxis profile as well as pathways regulating cytoskeleton and basement membrane remodeling.

Project description:BackgroundInflammation strongly contributes to atherosclerosis initiation and progression. Consequently, recent clinical trials pharmacologically targeted vascular inflammation to decrease the incidence of atherosclerosis-related complications. Colchicine, a microtubule inhibitor with anti-inflammatory properties, reduced cardiovascular events in patients with recent acute coronary syndrome and chronic coronary disease. However, the biological basis of these observations remains elusive. We sought to explore the mechanism by which colchicine beneficially alters the course of atherosclerosis.Methods and resultsIn mice with early atherosclerosis (Apoe-/- mice on a high cholesterol diet for 8 weeks), we found that colchicine treatment (0.25 mg/kg bodyweight once daily over four weeks) reduced numbers of neutrophils, inflammatory monocytes and macrophages inside atherosclerotic aortas using flow cytometry and immunohistochemistry. Consequently, colchicine treatment resulted in a less inflammatory plaque composition and reduced plaque size. We next investigated how colchicine prevented plaque leukocyte expansion and found that colchicine treatment mitigated recruitment of blood neutrophils and inflammatory monocytes to plaques as revealed by adoptive transfer experiments. Causally, we found that colchicine reduced levels of both leukocyte adhesion molecules and receptors for leukocyte chemoattractants on blood neutrophils and monocytes. Further experiments showed that colchicine treatment reduced vascular inflammation also in post-myocardial infarction accelerated atherosclerosis through similar mechanisms as documented in early atherosclerosis. When we examined whether colchicine also decreased numbers of macrophages inside atherosclerotic plaques by impacting monocyte/macrophage transitioning or in-situ proliferation of macrophages, we report that colchicine treatment did not influence macrophage precursor differentiation or macrophage proliferation using cell culture experiments with bone marrow derived macrophages.ConclusionsOur data reveal that colchicine prevents expansion of plaque inflammatory leukocytes through lowering recruitment of blood myeloid cells to plaques. These data provide novel mechanistic clues on the beneficial effects of colchicine in the treatment of atherosclerosis and may inform future anti-inflammatory interventions in patients at risk.

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Endoscopic photoconversion reveals unexpectedly broad leukocyte trafficking to and from the gut.

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