Occludin loss enhances paracellular macromolecular permeability (radius up to ∼62.5 Å) and is necessary for TNF-induced barrier loss. The latter requires the C-terminal OCEL domain, which stabilizes tight junction–associated occludin and regulates trafficking. Thus OCEL-mediated interactions are critical regulators of macromolecular paracellular flux.

Background & Aims Intraepithelial lymphocytes that express the γδ T cell receptor (γδ IELs) limit pathogen translocation across the intestinal epithelium by unknown mechanisms. We investigated whether γδ IEL migration and interaction with epithelial cells promote mucosal barrier maintenance during enteric infection. Methods Salmonella typhimurium or Toxoplasma gondii were administered to γδ T cell-deficient (Tcrd KO), CD103-deficient (CD103 KO), or control TcrdEGFP C57BL/6 reporter mice. Intravital microscopy was used to visualize migration of GFP-tagged γδ T cells within the small intestinal mucosa of mice infected with DsRed-labeled S typhimurium. Mixed bone marrow chimeras were generated to assess the effects of γδ IEL migration on early pathogen invasion and chronic systemic infection. Results Morphometric analyses of intravital video microscopy data showed that γδ IELs rapidly localized to and remained near epithelial cells in direct contact with bacteria. Within 1 hr, greater numbers of T gondii or S typhimurium were present within mucosae of mice with migration-defective occludin KO γδ T cells, compared with controls. Pathogen invasion in Tcrd KO mice was quantitatively similar to that in mice with occludin-deficient γδ T cells, whereas invasion in CD103 KO mice, which have increased migration of γδ T cells into the lateral intercellular space, was reduced by 63%. Consistent with a role of γδ T cell migration in early host defense, systemic salmonellosis developed more rapidly and with greater severity in mice with occludin-deficient γδ IELs, relative to those with wild-type or CD103 KO γδ IELs. Conclusions In mice, intraepithelial migration to epithelial cells in contact with pathogens is essential to γδ IEL surveillance and immediate host defense. γδ IEL occludin is required for early surveillance that limits systemic disease.

The members of the large family of claudin proteins regulate ion and water flux across the tight junction. Many claudins, e.g. claudins 2 and 15, accomplish this by forming size-and chargeselective paracellular channels. Claudins also appear to be essential for genesis of tight junction strands and recruitment of other proteins to these sites. What is less clear is whether claudins also form the paracellular seal. While this seal is defective when claudins are disrupted, some results, including ultrastructural and biochemical data, suggest that lipid structures are an important component of tight junction strands and may be responsible for the paracellular seal. This review highlights the current knowledge of claudins to barrier function and tight junction structure and suggests a model by which claudins and other tight junction proteins can drive assembly and stabilization of a lipid-based strand structure.

SUMMARY Type 2 diabetes (T2D) is associated with increased risk for atherosclerosis; however, the mechanisms underlying this relationship are poorly understood. Macrophages, which are activated in T2D and causatively linked to atherogenesis, are an attractive mechanistic link. Here, we use proteomics to show that diet-induced obesity and insulin resistance (obesity/IR) modulate a pro-atherogenic “macrophage-sterol-responsive-network” (MSRN), which, in turn, predisposes macrophages to cholesterol accumulation. We identify IFNγ as the mediator of obesity/IR-induced MSRN dysregulation and increased macrophage cholesterol accumulation and show that obesity/IR primes T cells to increase IFNγ production. Accordingly, myeloid cell-specific deletion of the IFNγ receptor (Ifngr1−/−) restores MSRN proteins, attenuates macrophage cholesterol accumulation and atherogenesis, and uncouples the strong relationship between hyperinsulinemia and aortic root lesion size in hypercholesterolemic Ldlr−/− mice with obesity/IR, but does not affect these parameters in Ldlr−/− mice without obesity/IR. Collectively, our findings identify an IFNγ-macrophage pathway as a mechanistic link between obesity/IR and accelerated atherogenesis.

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