Neural circuits regulate cytokine production to prevent potentially damaging inflammation. A prototypical vagus nerve circuit, the inflammatory reflex, inhibits tumor necrosis factor–α production in spleen by a mechanism requiring acetylcholine signaling through the α7 nicotinic acetylcholine receptor expressed on cytokine-producing macrophages. Nerve fibers in spleen lack the enzymatic machinery necessary for acetylcholine production; therefore, how does this neural circuit terminate in cholinergic signaling? We identified an acetylcholine-producing, memory phenotype T cell population in mice that is integral to the inflammatory reflex. These acetylcholine-producing T cells are required for inhibition of cytokine production by vagus nerve stimulation. Thus, action potentials originating in the vagus nerve regulate T cells, which in turn produce the neurotransmitter, acetylcholine, required to control innate immune responses.
Appropriate control of immune responses is a critical determinant of health. Here, we show that choline acetyltransferase (ChAT) is expressed and ACh is produced by B cells and other immune cells that have an impact on innate immunity. ChAT expression occurs in mucosal-associated lymph tissue, subsequent to microbial colonization, and is reduced by antibiotic treatment. MyD88-dependent Toll-like receptor up-regulates ChAT in a transient manner. Unlike the previously described CD4 + T-cell population that is stimulated by norepinephrine to release ACh, ChAT + B cells release ACh after stimulation with sulfated cholecystokinin but not norepinephrine. ACh-producing B-cells reduce peritoneal neutrophil recruitment during sterile endotoxemia independent of the vagus nerve, without affecting innate immune cell activation. Endothelial cells treated with ACh in vitro reduced endothelial cell adhesion molecule expression in a muscarinic receptor-dependent manner. Despite this ability, ChAT + B cells were unable to suppress effector T-cell function in vivo. Therefore, ACh produced by lymphocytes has specific functions, with ChAT + B cells controlling the local recruitment of neutrophils.
Enterohemorrhagic Escherichia coli O157:H7 (EHEC) is an enteric pathogen that causes potentially fatal symptoms after intimate adhesion, modulation of intestinal epithelial signal transduction, and alteration of epithelial function (eg, barrier disruption). Although the epithelial barrier is critical to gut homeostasis, only a few agents, such as transforming growth factor (TGF)-beta, can enhance or protect epithelial barrier function. Our aims were to delineate the mechanism(s) behind TGF-beta-induced barrier enhancement and to determine whether TGF-beta could prevent EHEC-induced barrier disruption. Using monolayers of the human T84 colonic epithelial cell line, we found that TGF-beta induced a significant increase in transepithelial electrical resistance (a measure of paracellular permeability) through activation of ERK MAPK and SMAD signaling pathways and up-regulation of the tight junction protein claudin-1. Additionally, TGF-beta pretreatment of epithelia blocked the decrease in transepithelial electrical resistance and the increase in transepithelial passage of [(3)H]-mannitol caused by EHEC infection. EHEC infection was associated with reduced expression of zonula occludens-1, occludin, and claudin-2 (but not claudin-1 or claudin-4); TGF-beta pretreatment prevented these changes. These studies provide insight into EHEC pathogenesis by illustrating the mechanisms underlying TGF-beta-induced epithelial barrier enhancement and identifying TGF-beta as an agent capable of blocking EHEC-induced increases in epithelial permeability via maintenance of claudin-2, occludin, and zonula occludens-1 levels.
Recent discoveries demonstrate a critical role for circadian rhythms and sleep in immune system homeostasis. Both innate and adaptive immune responses-ranging from leukocyte mobilization, trafficking, and chemotaxis to cytokine release and T cell differentiation-are mediated in a time of day-dependent manner. The National Institutes of Health (NIH) recently sponsored an interdisciplinary workshop, "Sleep Insufficiency, Circadian Misalignment, and the Immune Response," to highlight new research linking sleep and circadian biology to immune function and to identify areas of high translational potential. This Review summarizes topics discussed and highlights immediate opportunities for delineating clinically relevant connections among biological rhythms, sleep, and immune regulation. Circadian rhythms are daily variations in behavior and biological activity that stem from an intrinsic ability of organisms to align themselves with the environmental 24-hour light/dark cycle. These rhythms originate from an internal biological clock that drives many aspects of human physiology, including the sleepwake cycle and daily variations in blood pressure, body temperature, and cortisol (1). A growing body of epidemiological evidence demonstrates an association between altering circadian timing through shift work or frequent time zone travel and increased rates of cardiovascular disorders, metabolic syndrome, and cancer (2-4). Clinical aspects of disease such as pain perception, asthma exacerbations, and myocardial infarctions are more common at certain times of day or night (5, 6). The discovery of the genetic basis for the circadian clock in the 1980s and 1990s has ushered in a new era in which long-appreciated circadian rhythms in physiology and clinical medicine are being reframed in terms of gene expression, metabolism, signal transduction, and cellular physiology (7). The translation of circadian discovery into strategies to improve the prevention and management of disease promises to be transformative, but at present, fundamental research is outpacing clinical application (Figure 1A). Much will depend on research identifying the critical mechanisms and targets to which circadian rhythm-based therapeutic strategies can be applied. An emerging example of exciting circadian discovery with potential clinical relevance is the intersection between circadian function and immune regulation (Figure 1B). The NIH recently sponsored a workshop entitled "Sleep Insufficiency, Circadian Misalignment, and the Immune Response" (May 16-17, 2019, Rockville, Maryland, USA). Its aim was to highlight basic and clinical advances linking sleep and circadian biology to immune dysfunction, thereby stimulating the application of circadian biology to translational medicine. The Workshop was cosponsored by four NIH institutes-the National Heart, Lung, and Blood Institute (NHLBI), National Institute on Aging (NIA), National Institute of Allergy and Infectious Diseases (NIAID), and National Institute on Alcohol Abuse and Alcoholism (NIAAA)-reflecting a...
The IgM Fc receptor (FcμR), originally cloned as “Fas-apoptosis inhibitory molecule (FAIM3/TOSO)” can function as a cell surface receptor for secreted IgM on a variety of cell types. We report that FcμR also is expressed in the trans-Golgi network of developing B cells, where it constrains IgM- but not IgD-BCR transport. In FcμR absence, IgM-BCR surface expression was increased, resulting in enhanced tonic BCR signaling. B cell-specific FcμR-deficiency enhanced spontaneous differentiation of B-1 cells, resulting in increases in natural IgM levels, and dysregulated B-2 cell homeostasis, causing spontaneous germinal center formation, increased serum autoantibody titers, and excessive B cell accumulation. Thus, FcμR/FAIM3 is a critical regulator of B cell biology by constraining IgM-BCR transport and cell surface expression.
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