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In a review this month, Greer and co-authors present interesting information on just how much our health depends on the well-being and communal balance of the microscopic symbionts in our gastrointestinal tract [ Journal of Allergy and Clinical Immunology 2013; 132(2): 253-262 ].  They begin their review noting that, until fairly recently, immunity, metabolic functions and gut physiology had been studied as separate biological systems.  In light of growing evidence that the delineation between these is arbitrary, the authors point out that systems biology has developed new methods for investigating the interactions between the intestinal microbiota and immune and metabolic outcomes. Greer et al covers two broad categories, small intestine enteropathies and obesity with metabolic syndrome.  They describe current animal models used to study immunodeficiency enteropathies, celiac disease, inflammatory bowel disease, obesity and lipid metabolism dysregulation. The authors di...

Apoptosis was previously thought to be the only mode of regulated or programmed cell death in eosinophils, as necrosis was regarded as unregulated cell death.  However, Kano et al. , have discovered that the activated eosinophils, found in abundance in asthma and allergic disease, can die by means of a type of regulated necrosis in response to Siglec-8 ligation [ J Allergy Clin Immunol 2013; 132(2): 437-445 ]. Siglec-8 is a cell-surface receptor protein that is highly and selectively expressed by human eosinophils, as well as mast cells and basophils. The authors show that Siglec-8 ligation in the presence of IL-5 triggers necrosis in activated eosinophils in a reactive oxygen species (ROS) – dependent manner. Further, they explain why IL-5 promotes cell death in this system even though it is typically a pro-survival signal.  They demonstrate that ROS switch IL-5’s function from pro-survival to cell death enhancement by augmenting ERK phosphorylation and this serves as a decis...

Highlighting the role of innate immunity in the evolution of obesity and associated metabolic disorders, Jin and Flavell deliver a concise review of mechanisms involving pattern recognition receptors that produce pathology in liver, pancreas, brain and intestinal microbiota [ J Allergy Clin Immunol 2013; 132(2):287-294 ].  The authors provide a summary of the biology of the major types of pattern recognition receptors [PRR], with emphasis on toll-like receptors [TLR] and NOD-like receptors [NLR].  They discuss briefly their activity in response to pathogen infection and endogenous injury.  Several NLRs can coalesce into multiprotein complexes called inflammasomes which have proven to be important ly involved in the development of insulin resistance.  Jin and Flavell review PRR mechanisms in five critical physiologic areas: brain, pancreatic islet, and vascular inflammation, induction of peripheral insulin resistance, and disruption of intestinal microbiota homeos...