Tuft cell-derived acetylcholine regulates epithelial fluid secretion

Tuft cells are solitary chemosensory epithelial cells that can sense lumenal stimuli at mucosal barriers and secrete effector molecules to regulate the physiology and immune state of their surrounding tissue. In the small intestine, tuft cells detect parasitic worms (helminths) and microbe-derived succinate, and signal to immune cells to trigger a Type 2 immune response that leads to extensive epithelial remodeling spanning several days. Acetylcholine (ACh) from airway tuft cells has been shown to stimulate acute changes in breathing and mucocilliary clearance, but its function in the intestine is unknown. Here we show that tuft cell chemosensing in the intestine leads to release of ACh, but that this does not contribute to immune cell activation or associated tissue remodeling. Instead, tuft cell-derived ACh triggers immediate fluid secretion from neighboring epithelial cells into the intestinal lumen. This tuft cell-regulated fluid secretion is amplified during Type 2 inflammation, and helminth clearance is delayed in mice lacking tuft cell ACh. The coupling of the chemosensory function of tuft cells with fluid secretion creates an epithelium-intrinsic response unit that effects a physiological change within seconds of activation. This response mechanism is shared by tuft cells across tissues, and serves to regulate the epithelial secretion that is both a hallmark of Type 2 immunity and an essential component of homeostatic maintenance at mucosal barriers.

Initiation of type 2 immunity at barrier surfaces

Although seemingly unrelated, parasitic worms, venoms, and allergens all induce a type 2 immune response. The effector functions and clinical features of type 2 immunity are well-defined, but fundamental questions about the initiation of type 2 immunity remain unresolved. How are these enormously diverse type 2 stimuli first detected? How are type 2 helper T cells primed and regulated? And how do mechanisms of type 2 initiation vary across tissues? Here, we review the common themes governing type 2 immune sensing and explore aspects of T cell priming and effector reactivation that make type 2 helper T cells a unique T helper lineage. Throughout the review, we emphasize the importance of non-hematopoietic cells and highlight how the unique anatomy and physiology of each barrier tissue shape mechanisms of type 2 immune initiation.

Effector memory CD4 T cells engage myeloid cells through TNFR and CD40 to induce innate inflammation and autoimmune pathology independent of pattern recognition receptors

T cell mediated autoimmune diseases and associated tissue pathology is commonly attributed to inflammatory cytokines produced by the innate immune system. Similarly, CAR-T cell therapy and checkpoint blockades lead to innate cytokine storms and inflammation. While blocking individual cytokines can alleviate some of this pathology, the upstream mechanisms permitting self-reactive T cells to facilitate an innate inflammatory response remain unknown. We have discovered critical players that are engaged by effector memory CD4 (Tem) T cells to induce a broad transcriptional program in cells of the innate immune system. The pro-inflammatory response induced in innate immune cells is independent of pattern recognition receptors (PRRs), but mirrors genes induced by microbial recognition. We find that the innate inflammation is driven by combined engagement of TNFR and CD40 on myeloid cells presenting cognate antigen to Tem cells. Pro-inflammatory cytokine production and autoimmune pathology can be completely rescued by ablating the CD40 and TNFR pathways in several models of T cell driven inflammation. Thus, we have discovered a previously unknown trigger of innate inflammation and autoimmune pathology and propose that targeting this signaling node could be a more effective therapeutic approach than previously characterized cytokine-specific remedies.

Supported by grant from NIH (R01 AI123176)

Effector memory CD4+ T cells induce damaging innate inflammation and autoimmune pathology by engaging CD40 and TNFR on myeloid cells

Cytokine storm and sterile inflammation are common features of T cell-mediated autoimmune diseases and T cell-targeted cancer immunotherapies. Although blocking individual cytokines can mitigate some pathology, the upstream mechanisms governing overabundant innate inflammatory cytokine production remain unknown. Here, we have identified a critical signaling node that is engaged by effector memory T cells (T_EM) to mobilize a broad proinflammatory program in the innate immune system. Cognate interactions between T_EM and myeloid cells led to induction of an inflammatory transcriptional profile that was reminiscent, yet entirely independent, of classical pattern recognition receptor (PRR) activation. This PRR-independent "de novo" inflammation was driven by preexisting T_EM engagement of both CD40 and tumor necrosis factor receptor (TNFR) on myeloid cells. Cytokine toxicity and autoimmune pathology could be completely rescued by ablating these pathways genetically or pharmacologically in multiple models of T cell-driven inflammation, indicating that T_EM instruction of the innate immune system is a primary driver of associated immunopathology. Thus, we have identified a previously unknown trigger of cytokine storm and autoimmune pathology that is amenable to therapeutic interventions.

Innate control of adaptive immunity and adaptive instruction of innate immunity: bi-directional flow of information

The ability of the innate and adaptive immune systems to communicate with each other is central to protective immune responses and maintenance of host health. Myeloid cells of the innate immune system are able to sense microbial ligands, perturbations in cellular homeostasis, and virulence factors, thereby allowing them to relay distinct pathogen-specific information to naïve T cells in the form of pathogen-derived peptides and a unique cytokine milieu. Once primed, effector T helper cells produce lineage-defining cytokines to help combat the original pathogen, and a subset of these cells persist as memory or effector-memory populations. These memory T cells then play a dual role in host protection by not only responding rapidly to reinfection, but by also directly instructing myeloid cells to express licensing cytokines. This means there is a bi-directional flow of information first from the innate to the adaptive immune system, and then from the adaptive back to innate immune system. Here, we focus on how signals, first from pathogens and then from primed effector and memory T cells, are integrated by myeloid cells and its consequences for protective immunity or systemic inflammation.

Suppression of Inflammasome Activation by IRF8 and IRF4 in cDCs Is Critical for T Cell Priming

Inflammasome activation leads to pyroptotic cell death, thereby eliminating the replicative niche of virulent pathogens. Although inflammasome-associated cytokines IL-1β and IL-18 have an established role in T cell function, whether inflammasome activation in dendritic cells (DCs) is critical for T cell priming is not clear. Here, we find that conventional DCs (cDCs) suppress inflammasome activation to prevent pyroptotic cell death, thus preserving their ability to prime both CD4 and CD8 T cells. Transcription factors IRF8 and IRF4, in cDC1s and cDC2s, respectively, mediate suppression of inflammasome activation by limiting the expression of inflammasome-associated genes. Overexpression of IRF4 or IRF8 inhibits inflammasome activation in macrophages, while reduced expression of IRF8 leads to aberrant inflammasome activation in cDC1s and hampers their ability to prime CD8 T cells. Thus, activation of inflammasome in DCs is detrimental to adaptive immunity, and our results reveal that cDCs use IRF4 and IRF8 to suppress this response.

The role of inflammasome activation in eliciting adaptive immune responses against pathogens is poorly understood. McDaniel et al. demonstrate that conventional dendritic cells use IRF4 and IRF8 to suppress the transcription of inflammasome-associated machinery. This resulting suppression of inflammasome activation allows DCs to prime T cell responses against virulent pathogens.

IRF1 governs the differential interferon-stimulated gene responses in human monocytes and macrophages by regulating chromatin accessibility

Myeloid lineage cells use TLRs to recognize and respond to diverse microbial ligands. Although unique transcription factors dictate the outcome of specific TLR signaling, whether lineage-specific differences exist to further modulate the quality of TLR-induced inflammation remains unclear. Comprehensive analysis of global gene transcription in human monocytes, monocyte-derived macrophages, and monocyte-derived dendritic cells stimulated with various TLR ligands identifies multiple lineage-specific, TLR-responsive gene programs. Monocytes are hyperresponsive to TLR7/8 stimulation that correlates with the higher expression of the receptors. While macrophages and monocytes express similar levels of TLR4, macrophages, but not monocytes, upregulate interferon-stimulated genes (ISGs) in response to TLR4 stimulation. We find that TLR4 signaling in macrophages uniquely engages transcription factor IRF1, which facilitates the opening of ISG loci for transcription. This study provides a critical mechanistic basis for lineage-specific TLR responses and uncovers IRF1 as a master regulator for the ISG transcriptional program in human macrophages.

An amino acid change in IRF7 increases SLE risk through transcriptional regulation of type I interferons

Systemic Lupus Erythematosus (SLE) is an incurable, debilitating autoimmune disease characterized by widespread inflammation and rampant production of autoantibodies. The most prominent and highly replicated set of genes up-regulated in the immune cells of patients with SLE are the type I interferons (IFN-I) and IFN-responsive genes. IFN-I are predominantly made by plasmacytoid dendritic cells (pDCs), and their expression is directly regulated by the transcription factor interferon regulatory factor 7 (IRF7). While IRF7 is an established SLE risk locus, the variants responsible for disease pathology remain unknown. We hypothesize that an amino-acid changing SLE risk variant in IRF7 (rs1131665) alters expression of disease-relevant IFN-I in clinically-relevant cells to increase SLE risk. The functional genomic consequences of the SLE-associated variant were assessed in human cell lines and in genome-edited mice with an introduced SLE-risk variant at Irf7. Our data demonstrate greater than 2-fold genotype-dependence in IFN-stimulated response element-driven luciferase activity and inflammatory cytokine secretion detected in supernatant after toll-like receptor-7 stimulation. Gene expression differences in cells with IRF7/Irf7 risk variants are consistent with those dysregulated in SLE patients. In the present study, we demonstrate the functional consequences of an amino acid substitution in a critical type I interferon regulator. Understanding these mechanisms will enhance development of more effective clinical practices for autoimmune patients expressing the risk variant for IRF7.

Estimating Residence Times of Lymphocytes in Ovine Lymph Nodes

The ability of lymphocytes to recirculate between blood and secondary lymphoid tissues such as lymph nodes (LNs) and spleen is well established. Sheep have been used as an experimental system to study lymphocyte recirculation for decades and multiple studies document accumulation and loss of intravenously (i.v.) transferred lymphocytes in efferent lymph of various ovine LNs. Yet, surprisingly little work has been done to accurately quantify the dynamics of lymphocyte exit from the LNs and to estimate the average residence times of lymphocytes in ovine LNs. In this work we developed a series of mathematical models based on fundamental principles of lymphocyte recirculation in the body under non-inflammatory (resting) conditions. Our analysis suggested that in sheep, recirculating lymphocytes spend on average 3 h in the spleen and 20 h in skin or gut-draining LNs with a distribution of residence times in LNs following a skewed gamma (lognormal-like) distribution. Our mathematical models also suggested an explanation for a puzzling observation of the long-term persistence of i.v. transferred lymphocytes in the efferent lymph of the prescapular LN (pLN); the model predicted that this is a natural consequence of long-term persistence of the transferred lymphocytes in circulation. We also found that lymphocytes isolated from the skin-draining pLN have a 2-fold increased entry rate into the pLN as opposed to the mesenteric (gut-draining) LN (mLN). Likewise, lymphocytes from mLN had a 3-fold increased entry rate into the mLN as opposed to entry rate into pLN. In contrast, these cannulation data could not be explained by preferential retention of cells in LNs of their origin. Taken together, our work illustrates the power of mathematical modeling in describing the kinetics of lymphocyte migration in sheep and provides quantitative estimates of lymphocyte residence times in ovine LNs.

Severe Gut Microbiota Dysbiosis Is Associated With Poor Growth in Patients With Short Bowel Syndrome

BACKGROUND

Children with short bowel syndrome (SBS) can vary significantly in their growth trajectory. Recent data have shown that children with SBS possess a unique gut microbiota signature compared with healthy controls. We hypothesized that children with SBS and poor growth would exhibit more severe gut microbiota dysbiosis compared with those with SBS who are growing adequately, despite similar intestinal anatomy.

MATERIALS AND METHODS

Stool samples were collected from children with SBS (n = 8) and healthy controls (n = 3) over 3 months. Gut microbiota populations (16S ribosomal RNA sequencing and metagenomic shotgun sequencing) were compared, including a more in-depth analysis of SBS children exhibiting poor and good growth. Statistical analysis was performed using Mann-Whitney, Kruskal-Wallis, and χ² tests as appropriate.

RESULTS

Children with SBS had a significant deficiency of the commensal Firmicutes order Clostridiales ( P = .025, Kruskal-Wallis) compared with healthy children. Furthermore, children with SBS and poor growth were deficient in beneficial bacteria known to produce short-chain fatty acids and had expansion of proinflammatory Enterobacteriaceae ( P = .038, Kruskal-Wallis) compared with children with SBS who were growing adequately. Using metabolic function analyses, SBS/poor growth microbiomes were deficient in genes needed for gluconeogenesis but enriched in branched and aromatic amino acid synthesis and citrate cycle pathway genes.

CONCLUSIONS

Patients with SBS, particularly those with suboptimal growth, have a marked gut dysbiosis characterized by a paucity of beneficial commensal anaerobes, resulting in a deficiency of key metabolic enzymes found in the gut microbiomes of healthy children.

Quantifying Limits on Replication, Death, and Quiescence of Mycobacterium tuberculosis in Mice

When an individual is exposed to Mycobacterium tuberculosis (Mtb) three outcomes are possible: bacterial clearance, active disease, or latent infection. It is generally believed that most individuals exposed to Mtb become latently infected and carry the mycobacteria for life. How Mtb is maintained during this latent infection remains largely unknown. During an Mtb infection in mice, there is a phase of rapid increase in bacterial numbers in the murine lungs within the first 3 weeks, and then bacterial numbers either stabilize or increase slowly over the period of many months. It has been debated whether the relatively constant numbers of bacteria in the chronic infection result from latent (dormant, quiescent), non-replicating bacteria, or whether the observed Mtb cell numbers are due to balance between rapid replication and death. A recent study of mice, infected with a Mtb strain carrying an unstable plasmid, showed that during the chronic phase, Mtb was replicating at significant rates. Using experimental data from this study and mathematical modeling we investigated the limits of the rates of bacterial replication, death, and quiescence during Mtb infection of mice. First, we found that to explain the data the rates of bacterial replication and death could not be constant and had to decrease with time since infection unless there were large changes in plasmid segregation probability over time. While a decrease in the rate of Mtb replication with time since infection was expected due to depletion of host's resources, a decrease in the Mtb death rate was counterintuitive since Mtb-specific immune response, appearing in the lungs 3–4 weeks after infection, should increase removal of bacteria. Interestingly, we found no significant correlation between estimated rates of Mtb replication and death suggesting the decline in these rates was driven by independent mechanisms. Second, we found that the data could not be explained by assuming that bacteria do not die, suggesting that some removal of bacteria from lungs of these mice had to occur even though the total bacterial counts in these mice always increased over time. Third and finally, we showed that to explain the data the majority of bacterial cells (at least ~60%) must be replicating in the chronic phase of infection further challenging widespread belief of nonreplicating Mtb in latency. Our predictions were robust to some changes in the structure of the model, for example, when the loss of plasmid-bearing cells was mainly due to high fitness cost of the plasmid. Further studies should determine if more mechanistic models for Mtb dynamics are also able to accurately explain these data.

Noise exposure and hearing loss prevention programmes after 20 years of regulations in the United States

OBJECTIVES

To evaluate noise exposures and hearing loss prevention efforts in industries with relatively high rates of workers' compensation claims for hearing loss.

METHODS

Washington State workers' compensation records were used to identify up to 10 companies in each of eight industries. Each company (n = 76) was evaluated by a management interview, employee personal noise dosimetry (n = 983), and employee interviews (n = 1557).

RESULTS

Full-shift average exposures were > or =85 dBA for 50% of monitored employees, using Occupational Safety and Health Administration (OSHA) parameters with a 5 dB exchange rate (L(ave)), but 74% were > or =85 dBA using a 3 dB exchange rate (L(eq)). Only 14% had L(ave) > or =90 dBA, but 42% had L(eq) > or =90 dBA. Most companies conducted noise measurements, but most kept no records, and consideration of noise controls was low in all industries. Hearing loss prevention programmes were commonly incomplete. Management interview scores (higher score = more complete programme) showed significant associations with percentage of employees having L(ave) > or =85 dBA and presence of a union (multiple linear regression; R2 = 0.24). Overall, 62% of interviewed employees reported always using hearing protection when exposed. Protector use showed significant associations with percentage of employees specifically required to use protection, management score, and average employee time spent > or =95 dBA (R2 = 0.65).

CONCLUSIONS

The findings raise serious concerns about the adequacy of prevention, regulation, and enforcement strategies in the United States. The percentage of workers with excessive exposure was 1.5-3 times higher using a 3 dB exchange rate instead of the OSHA specified 5 dB exchange rate. Most companies gave limited or no attention to noise controls and relied primarily on hearing protection to prevent hearing loss; yet 38% of employees did not use protectors routinely. Protector use was highest when hearing loss prevention programmes were most complete, indicating that under-use of protection was, in some substantial part, attributable to incomplete or inadequate company efforts.

Iatrogenic false-positive findings on cardiac scans

Two patients subjected to cardiopulmonary resuscitation with chest massage and direct-current cardioversion had positive activity on myocardial scintiscans using radioactive 99mtechnetium pyrophosphate. Possible explanations are offered, and recent reports of false-positive findings on scans due to organic disease, as well as iatrogenic causes, are discussed briefly.