Active eosinophils regulate host defence and immune responses in colitis.

In the past decade, single-cell transcriptomics has helped to uncover new cell types and states and led to the construction of a cellular compendium of health and disease. Despite this progress, some difficult-to-sequence cells remain absent from tissue atlases. Eosinophils-elusive granulocytes that are implicated in a plethora of human pathologies1-5-are among these uncharted cell types. The heterogeneity of eosinophils and the gene programs that underpin their pleiotropic functions remain poorly understood. Here we provide a comprehensive single-cell transcriptomic profiling of mouse eosinophils. We identify an active and a basal population of intestinal eosinophils, which differ in their transcriptome, surface proteome and spatial localization. By means of a genome-wide CRISPR inhibition screen and functional assays, we reveal a mechanism by which interleukin-33 (IL-33) and interferon-γ (IFNγ) induce the accumulation of active eosinophils in the inflamed colon. Active eosinophils are endowed with bactericidal and T cell regulatory activity, and express the co-stimulatory molecules CD80 and PD-L1. Notably, active eosinophils are enriched in the lamina propria of a small cohort of patients with inflammatory bowel disease, and are closely associated with CD4+ T cells. Our findings provide insights into the biology of eosinophils and highlight the crucial contribution of this cell type to intestinal homeostasis, immune regulation and host defence. Furthermore, we lay a framework for the characterization of eosinophils in human gastrointestinal diseases.

Inulin fibre promotes microbiota-derived bile acids and type 2 inflammation.

Dietary fibres can exert beneficial anti-inflammatory effects through microbially fermented short-chain fatty acid metabolites^1,2, although the immunoregulatory roles of most fibre diets and their microbiota-derived metabolites remain poorly defined. Here, using microbial sequencing and untargeted metabolomics, we show that a diet of inulin fibre alters the composition of the mouse microbiota and the levels of microbiota-derived metabolites, notably bile acids. This metabolomic shift is associated with type 2 inflammation in the intestine and lungs, characterized by IL-33 production, activation of group 2 innate lymphoid cells and eosinophilia. Delivery of cholic acid mimics inulin-induced type 2 inflammation, whereas deletion of the bile acid receptor farnesoid X receptor diminishes the effects of inulin. The effects of inulin are microbiota dependent and were reproduced in mice colonized with human-derived microbiota. Furthermore, genetic deletion of a bile-acid-metabolizing enzyme in one bacterial species abolishes the ability of inulin to trigger type 2 inflammation. Finally, we demonstrate that inulin enhances allergen- and helminth-induced type 2 inflammation. Taken together, these data reveal that dietary inulin fibre triggers microbiota-derived cholic acid and type 2 inflammation at barrier surfaces with implications for understanding the pathophysiology of allergic inflammation, tissue protection and host defence.

More than neutrophils: Lin(+)Ly6G(+)IL-5Rα(+) multipotent myeloid cells (MMCs) are dominant in normal murine bone marrow and retain capacity to differentiate into eosinophils and monocytes.

Bone marrow is a hematopoietic site harboring multiple populations of myeloid cells in different stages of differentiation. Murine bone marrow eosinophils are traditionally identified by Siglec-F(+) staining using flow cytometry, whereas neutrophils are characterized by Ly6G(+) expression. However, using flow cytometry to characterize bone marrow hematopoietic cells in wild-type mice, we found substantial gray areas in identification of these cells. Siglec-F(+) mature eosinophil population constituted only a minority of bone marrow Lin(+)CD45(+) pool (5%). A substantial population of Siglec-F(-) cells was double positive for neutrophil marker Ly6G and eosinophil lineage marker, IL-5Rα. This granulocyte population with mixed neutrophil and eosinophil characteristics is typically attributable to neutrophil pool based on neutral granule staining and expression of Ly6G and myeloid peroxidase. It is distinct from Lineage(-) myeloid progenitors or Siglec-F(+)Ly6G(+) maturing eosinophil precursors, and can be accurately identified by Lineage(+) staining and positive expression of markers IL-5Rα and Ly6G. At 15-50% of all CD45(+) hematopoietic cells in adult mice (percentage varies by sex and age), this is a surprisingly dominant population, which increases with age in both male and female mice. RNA-seq characterization of these cells revealed a complex immune profile and the capacity to secrete constituents of the extracellular matrix. When sorted from bone marrow, these resident cells had neutrophilic phenotype but readily acquired all characteristics of eosinophils when cultured with G-CSF or IL-5, including expression of Siglec-F and granular proteins (Epx, Mbp). Surprisingly, these cells were also able to differentiate into Ly6C(+) monocytes when cultured with M-CSF. Herein described is the discovery of an unexpected hematopoietic flexibility of a dominant population of multipotent myeloid cells, typically categorized as neutrophils, but with the previously unknown plasticity to contribute to mature pools of eosinophils and monocytes.

Beyond eosinophilia: inflammatory patterns in patients with asthma.

Background: Recently, inflammatory cell ratios have gained importance as useful indicators in the categorization of asthma.Objective: We compared the concentration of white blood cells in peripheral blood, as well as their respective inflammatory cell ratios, between patients with asthma and a healthy control group.Methods: We performed cross-sectional analyses of the data obtained from 53 adult patients with asthma and 109 adult controls. In our study, we estimated and compared the following inflammatory cell ratios: Neutrophil-Lymphocyte Ratio (NLR), Eosinophil-Lymphocyte Ratio (ELR), Eosinophil-Neutrophil Ratio (ENR), Eosinophil-Monocyte Ratio (EMR), and Platelet-Lymphocyte Ratio (PLR). The magnitude of association was quantified with the odds ratio.Results: In both groups, the average age was 33 years. In asthmatic patients, we obtained the following results: eosinophils ≥ 400 cells/µl, accounted for 37.7%; basophils ≥ 110 cells/µl, comprised 37.7%; and monocytes < 320 cells/µl, reached 11.3%. In the control group, the results were as follows: 4.6%, 9.2% and 0.9%, respectively. When compared to the control group, asthmatic patients had higher odds of eosinophils ≥ 400 cells/µl (OR = 12.61, p < 0.0001); higher odds of basophils ≥ 110 cells/µl (OR = 6.00, p < 0.0001); and increased odds of monocytes < 320 cells/µl (OR = 13.79, p = 0.017). NLR did not differ between our two groups; however, ELR, ENR, EMR and PLR were significantly higher in the asthma group.Conclusions: Overall, patients with asthma have a higher concentration of eosinophils and basophils, fewer monocytes in their blood, and higher ratios of increased chronic inflammation.

Identification of inflammatory markers in eosinophilic cells of the immune system: fluorescence, Raman and CARS imaging can recognize markers but differently.

Eosinophils (Eos) play an important role in the immune system's response releasing several inflammatory factors and contributing to allergic rhinitis, asthma, or atopic dermatitis. Since Eos have a relatively short lifetime after isolation from blood, usually eosinophilic cell line (EoL-1) is used to study mechanisms of their activation and to test therapies. In particular, EoL-1 cells are examined in terms of signalling pathways of the inflammatory response manifested by the presence of lipid bodies (LBs). Here we examined the differences in response to inflammation modelled by various factors, between isolated human eosinophils and EoL-1 cells, as manifested in the number and chemical composition of LBs. The analysis was performed using fluorescence, Raman, and coherent anti-Stokes Raman scattering (CARS) microscopy, which recognised the inflammatory process in the cells, but it is manifested slightly differently depending on the method used. We showed that unstimulated EoL-1 cells, compared to isolated eosinophils, contained more LBs, displayed different nucleus morphology and did not have eosinophilic peroxidase (EPO). In EoL-1 cells stimulated with various proinflammatory agents, including butyric acid (BA), liposaccharide (LPS), or cytokines (IL-1ß, TNF-α), an increased production of LBs with a various degree of lipid unsaturation was observed in spontaneous Raman spectra. Furthermore, stimulation of EoL-1 cells resulted in alterations of the LBs morphology. In conclusion, a level of lipid unsaturation and eosinophilic peroxidase as well as LBs distribution among cell population mainly accounted for the biochemistry of eosinophils upon inflammation.

Isolation and characterization of eosinophils in bovine blood and small intestine.

An effective method to isolate functional eosinophils from blood and tissues is required to analyze the multiple roles eosinophils play in innate immunity and tissue homeostasis. Highspeed cell sorting was used to isolate bovine eosinophils from blood polymorphonuclear (PMN) cells and from small intestine intraepithelial leukocytes. Eosinophils and neutrophils were purified from bovine blood with highspeed cell sorting after gating on autofluorescence (FL1) high and low PMN subpopulations. Highspeed sorting of intestinal eosinophils was accomplished by using a combination of positive (CD45+, CD11cLow, side scatterHigh) and negative (CD3-) selection parameters. Eosinophils sorted from blood PMNs were 88.6 ± 5.8 % (mean + 1 SD; n = 4) pure and yielded significantly (p < 0.05) more RNA than purified neutrophils. Analysis of Toll-like receptor (TLR) gene expression and TLR ligand-induced pro-inflammatory cytokine (IL-1, IL-6, IL-8, and TNFα) gene expression demonstrated significant (p < 0.01) functional differences between blood eosinophils and neutrophils. Eosinophils varied between 14.7 % to 29.3 % of CD45+ IELs and purity of sorted intestinal eosinophils was 95 + 3.5 % (mean + 1SD; n = 5). A comparison of mucosal and blood eosinophils revealed significant (p < 0.01) differences in TLR gene expression, supporting the hypothesis that functionally distinct eosinophil populations are present in blood and tissues. In conclusion, highspeed cell sorting provides an effective method to isolate viable eosinophils from blood and tissues that can then be used for transcriptome analyses and in vitro function assays.

Eosinophils, beyond IL-5.

New therapeutic monoclonal antibodies targeting the IL-5/IL-5 receptor pathway are extremely efficient in depleting blood eosinophils from subjects with asthma [...].

Rat Blood Leukocytes after Intravenous Injection of Magnetoliposomes on the Basis of Nanomagnetite.

The structure of blood neutrophils, eosinophils, monocytes, and lymphocytes and differential white blood count in adult rats were studied over 120 days after a single intravenous injection of magnetoliposomes based on nanomagnetite. Magnetoliposomes had no effect on the structure of neutrophils, eosinophils, monocytes, and lymphocytes. At the same time, injection of a suspension of magnetoliposomes based on magnetite nanoparticles led to a decrease in lymphocyte count and an increase in the count of monocytes and band and segmented neutrophils in the blood. These changes were transient and the parameters returned to normal by day 40-60 after injection.

Risk Model Establishment of Endoscopic Sinus Surgery for Patients with Chronic Rhinosinusitis: a Multicenter Study in Korea.

BACKGROUND: Endoscopic sinus surgery (ESS) is the mainstay treatment for refractory chronic rhinosinusitis (CRS). Since various factors may contribute to the surgical outcome, it is challenging for physicians to predict surgical outcomes. The aim of study was to analyze the prognostic factors of postoperative outcomes and to establish the prediction model with the risk factors that impact the postoperative outcomes. METHODS: Medical records of CRS patients who underwent ESS at 9 institutions in 2005, 2010, and 2016 were retrospectively reviewed. We classified the patients into 2 groups based on postoperative objective endoscopic outcomes. Demographics, nose-specific symptoms, olfactory function, eosinophil counts in blood (EoB) and nasal tissue (EoT), and Lund-Mackay CT score (LMS) were collected. Univariate and multivariate analyses were performed and established a prediction equation for postoperative endoscopic objective outcomes. RESULTS: In total (n = 1,249), 27.0% were not satisfied under postoperative endoscopic examination. Of 10 variables, LMS (> 5), sinus dominancy (maxillary sinus and ethmoid sinus), EoB (> 210), and EoT (> 100) were statistically significant in univariate analysis (P < 0.05, all). In multivariate analysis, EoT (> 100) and LMS (> 5) were significantly associated with poor postoperative outcome. Furthermore, 5 significant variables were employed to establish the risk model of postoperative outcomes and P (the value of prediction probability) = 1 / (1 + exp [-0.392 + 1.088 × EoT (> 100) + 0.123 × mean LMS (> 5) - 0.366 × sinus dominancy (maxillary) + 0.064 × sinus dominancy (similar) + 0.200 × EoB (4%) + 0.344 × EoB (> 210)] was developed. CONCLUSION: Tissue eosinophil count and radiographic severity predispose to a poorer outcome of ESS and the risk model established may be helpful to predict postoperative outcomes of ESS.

Blood and immune development in human fetal bone marrow and Down syndrome.

Haematopoiesis in the bone marrow (BM) maintains blood and immune cell production throughout postnatal life. Haematopoiesis first emerges in human BM at 11-12 weeks after conception1,2, yet almost nothing is known about how fetal BM (FBM) evolves to meet the highly specialized needs of the fetus and newborn. Here we detail the development of FBM, including stroma, using multi-omic assessment of mRNA and multiplexed protein epitope expression. We find that the full blood and immune cell repertoire is established in FBM in a short time window of 6-7 weeks early in the second trimester. FBM promotes rapid and extensive diversification of myeloid cells, with granulocytes, eosinophils and dendritic cell subsets emerging for the first time. The substantial expansion of B lymphocytes in FBM contrasts with fetal liver at the same gestational age. Haematopoietic progenitors from fetal liver, FBM and cord blood exhibit transcriptional and functional differences that contribute to tissue-specific identity and cellular diversification. Endothelial cell types form distinct vascular structures that we show are regionally compartmentalized within FBM. Finally, we reveal selective disruption of B lymphocyte, erythroid and myeloid development owing to a cell-intrinsic differentiation bias as well as extrinsic regulation through an altered microenvironment in Down syndrome (trisomy 21).

REal worlD Effectiveness and Safety of Mepolizumab in a Multicentric Spanish Cohort of Asthma Patients Stratified by Eosinophils: The REDES Study.

BACKGROUND: The efficacy of mepolizumab is well documented in severe eosinophilic asthma (SEA), although the stringent selection criteria adopted by SEA clinical trials limits the generalizability of results. OBJECTIVE: Our study evaluated the effectiveness and safety of mepolizumab in patients with SEA in Spain. The primary efficacy endpoint was the change in the rate of clinically significant asthma exacerbations 12 months after starting mepolizumab compared to the baseline rate in the 12 months prior to treatment. Patients were stratified by baseline blood eosinophil counts. METHODS: We conducted a multicentric observational cohort study of SEA patients treated with mepolizumab across 24 specialized hospital asthma units in Spain. Severe exacerbation rate, lung function, oral corticosteroid use (OCS) and asthma control test (ACT) were retrospectively collected and compared during the 12-month pre- and post-mepolizumab treatment. Adverse events were also investigated. RESULTS: A total of 318 patients with SEA were included (mean age: 56.6 years, 69.2% female). Exacerbation rates decreased by 77.5%, and 50.6% of patients did not suffer any exacerbations during the 12 months of treatment. The difference in forced expiratory volume in 1 s (FEV1) pre- and post-bronchodilator after starting mepolizumab was 0.21 (0.46) L (95% CI 0.14-0.27) (p < 0.001). Exacerbations and lung function significantly improved across all eosinophil subgroups. Among the 98 patients on OCS, 47.8% were able to discontinue this treatment and the mean daily dose was decreased by 59.9%. The baseline ACT score was 14.1, increasing by a mean (SD) of 6.7 points (1.9) at 12 months. Adverse events related to mepolizumab were uncommon. CONCLUSIONS: This real-world study of SEA patients confirms that mepolizumab is effective in reducing clinically meaningful exacerbations, improving lung function, and decreasing OCS dependence and mean OCS dose at 12 months, irrespective of baseline eosinophil counts.

Eosinophil: A Nonnegligible Predictor in COVID-19 Re-Positive Patients.

Although vaccine resources are being distributed worldwide, insufficient vaccine production remains a major obstacle to herd immunity. In such an environment, the cases of re-positive occurred frequently, and there is a big controversy regarding the cause of re-positive episodes and the infectivity of re-positive cases. In this case-control study, we tracked 39 patients diagnosed with COVID-19 from the Jiaodong Peninsula area of China, of which 7 patients tested re-positive. We compared the sex distribution, age, comorbidities, and clinical laboratory results between normal patients and re-positive patients, and analysed the correlation between the significantly different indicators and the re-positive. Re-positive patients displayed a lower level of serum creatinine (63.38 ± 4.94 U/L vs. 86.82 ± 16.98 U/L; P =0.014) and lower albumin (34.70 ± 5.46 g/L vs. 41.24 ± 5.44 g/L, P =0.039) at the time of initial diagnosis. In addition, two positive phases and the middle negative phase in re-positive patients with significantly different eosinophil counts (0.005 ± 0.005 × 109/L; 0.103 ± 0.033 × 109/L; 0.007 ± 0.115 × 109/L; Normal range: 0.02-0.52 × 109/L). The level of eosinophils in peripheral blood can be used as a marker to predict re-positive in patients who once had COVID-19.

Severe asthma exacerbations in the United States:: Incidence, characteristics, predictors, and effects of biologic treatments.

BACKGROUND: Patients with severe asthma (SA) have a heightened risk of exacerbations including hospitalization. The real-world, specialist-verified incidence and characteristics of exacerbations among patients with SA in the United States have not been described. OBJECTIVE: To describe the real-world incidence, characteristics, and predictors of exacerbations among patients with SA in the United States. METHODS: The CHRONICLE study is an ongoing observational study of specialist-treated adults with SA in the United States receiving biologic treatment or maintenance systemic corticosteroids or uncontrolled by high-dosage inhaled corticosteroids with additional controllers. For patients enrolled from February 2018 to February 2020, annualized rates and characteristics of exacerbation-related events were summarized by treatment category for 12 months before enrollment and after enrollment through the latest data collection. Results were further analyzed for subgroups of interest. RESULTS: Among 1884 enrolled patients, 53.5% and 12.3% experienced an exacerbation and asthma hospitalization, respectively (0.81 and 0.14 per person-year). Of all exacerbations, 36%, 9%, and 15% required an unscheduled health care provider visit, emergency department visit without hospitalization, and hospitalization, respectively. Among patients not receiving biologics or systemic corticosteroids, higher blood eosinophil count, higher fractional exhaled nitric oxide, and lower total immunoglobulin E level were associated with higher exacerbation rates. Exacerbation rates decreased after starting or switching biologics (n = 1299). Multivariate analyses of enrolled patients revealed previous-year exacerbations or hospitalizations, lack of asthma control, and the geographic region also predicted event risk. CONCLUSION: In this real-world cohort of specialist-treated adults with SA in the United States, there was a substantial burden of exacerbations and associated health care resource utilization. Patients receiving biologics had a lower exacerbation burden. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03373045.

Emerging Evidence for Pleiotropism of Eosinophils.

Eosinophils are complex granulocytes with the capacity to react upon diverse stimuli due to their numerous and variable surface receptors, which allows them to respond in very different manners. Traditionally believed to be only part of parasitic and allergic/asthmatic immune responses, as scientific studies arise, the paradigm about these cells is continuously changing, adding layers of complexity to their roles in homeostasis and disease. Developing principally in the bone marrow by the action of IL-5 and granulocyte macrophage colony-stimulating factor GM-CSF, eosinophils migrate from the blood to very different organs, performing multiple functions in tissue homeostasis as in the gastrointestinal tract, thymus, uterus, mammary glands, liver, and skeletal muscle. In organs such as the lungs and gastrointestinal tract, eosinophils are able to act as immune regulatory cells and also to perform direct actions against parasites, and bacteria, where novel mechanisms of immune defense as extracellular DNA traps are key factors. Besides, eosinophils, are of importance in an effective response against viral pathogens by their nuclease enzymatic activity and have been lately described as involved in severe acute respiratory syndrome coronavirus SARS-CoV-2 immunity. The pleiotropic role of eosinophils is sustained because eosinophils can be also detrimental to human physiology, for example, in diseases like allergies, asthma, and eosinophilic esophagitis, where exosomes can be significant pathophysiologic units. These eosinophilic pathologies, require specific treatments by eosinophils control, such as new monoclonal antibodies like mepolizumab, reslizumab, and benralizumab. In this review, we describe the roles of eosinophils as effectors and regulatory cells and their involvement in pathological disorders and treatment.

Human pluripotent stem cell-derived eosinophils reveal potent cytotoxicity against solid tumors.

Eosinophils are attractive innate immune cells to use to potentiate T cell antitumor efficacy because they are capable of infiltrating tumors at early stages and modulating the tumor microenvironment. However, the limited number of functional eosinophils caused by the scarcity and short life of primary eosinophils in peripheral blood has greatly impeded the development of eosinophil-based immunotherapy. In this study, we established an efficient chemically defined protocol to generate a large quantity of functional eosinophils from human pluripotent stem cells (hPSCs) with nearly 100% purity expressing eosinophil peroxidase. These hPSC-derived eosinophils transcriptionally resembled their primary counterpart. Moreover, hPSC-derived eosinophils showed competent tumor killing capacity in established solid tumors. Furthermore, the combination of hPSC-derived eosinophils with CAR-T cells exhibited potential synergistic effects, inhibiting tumor growth and enhancing mouse survival. Our study opens up new avenues for the development of eosinophil-based immunotherapies to treat cancer.

Variability of blood eosinophil count and prognosis of COPD exacerbations.

BACKGROUND: Eosinophils in peripheral blood are one of the emerging biomarkers in chronic obstructive pulmonary disease (COPD) patients. However, when analysing the relationship between peripheral eosinophilia and COPD prognosis, highly variable results are obtained. The aim of our study is to describe the serum eosinophilia levels in COPD patients and to analyse their relationship to prognosis following hospital admission. METHODS: A prospective observational study was conducted from 1 October 2016 to 1 October 2018 in the following Spanish centres: Salnés County Hospital in Vilagarcía de Arousa, Arquitecto Marcide Hospital in Ferrol and the University Hospital Complex in Santiago de Compostela. The patients were classified using three cut-off points of blood eosinophil count (BEC): 150 cells/µL, 300 cells/µL, and 400 cells/µL; in addition, the peripheral BEC was analysed on admission. RESULTS: 615 patients were included in the study, 86.2% male, mean age 73.9 years, and mean FEV1 52.7%. The mean stay was 8.4 days, and 6% of all patients were readmitted early. No significant relationship was observed between the BEC, neither in the stable phase nor in the acute phase, and hospital stay, readmissions, deaths during admission, the need for intensive care, or the condition of frequent exacerbator. CONCLUSION: The results of our study do not seem to support the usefulness of BEC as a COPD biomarker.KEY MESSAGESThere is evidence that BEC participates in pathophysiological mechanisms of the COPD.BEC may be useful as a biomarker in COPD for aspects such as the optimization of treatments.We did not find any relationship between BEC levels and prognosis following hospital admission for AECOPD.

Neutrophil-to-lymphocyte ratio, platelets-to-lymphocyte ratio, and eosinophils correlation with high-resolution computer tomography severity score in COVID-19 patients.

Inflammation has an important role in the progression of various viral pneumonia, including COVID-19. Circulating biomarkers that can evaluate inflammation and immune status are potentially useful in diagnosing and prognosis of COVID-19 patients. Even more so when they are a part of the routine evaluation, chest CT could have even higher diagnostic accuracy than RT-PCT alone in a suggestive clinical context. This study aims to evaluate the correlation between inflammatory markers such as neutrophil-to-lymphocyte ratio (NLR), platelets-to-lymphocytes ratio (PLR), and eosinophils with the severity of CT lesions in patients with COVID-19. The second objective was to seek a statically significant cut-off value for NLR and PLR that could suggest COVID-19. Correlation of both NLR and PLR with already established inflammatory markers such as CRP, ESR, and those specific for COVID-19 (ferritin, D-dimers, and eosinophils) were also evaluated. One hundred forty-nine patients with confirmed COVID-19 disease and 149 age-matched control were evaluated through blood tests, and COVID-19 patients had thorax CT performed. Both NLR and PLR correlated positive chest CT scan severity. Both NLR and PLR correlated positive chest CT scan severity. When NLR value is below 5.04, CT score is lower than 3 with a probability of 94%, while when NLR is higher than 5.04, the probability of severe CT changes is only 50%. For eosinophils, a value of 0.35% corresponds to chest CT severity of 2 (Se = 0.88, Sp = 0.43, AUC = 0.661, 95% CI (0.544; 0.779), p = 0.021. NLR and PLR had significantly higher values in COVID-19 patients. In our study a NLR = 2.90 and PLR = 186 have a good specificity (0.89, p = 0.001, respectively 0.92, p<0.001). Higher levels in NLR, PLR should prompt the clinician to prescribe a thorax CT as it could reveal important lesions that could influence the patient's future management.

Neutrophils, eosinophils, and intraepithelial lymphocytes in the squamous esophagus in subjects with and without gastroesophageal reflux symptoms.

Whilst intraepithelial lymphocytes (IELs) are considered normal within the distal esophageal mucosa, they have an increasingly recognised role in the pathogenesis of reflux esophagitis, and IEL quantification establishes the diagnosis of lymphocytic esophagitis. Knowledge regarding the upper limit of a normal IEL count in health is lacking. We studied 117 non-healthcare seeking adult volunteers from a random community sample (the Kalixanda study) with esophageal biopsies 2 cm above the gastroesophageal junction. Subjects were divided into four groups based on the presence or absence of gastro-esophageal reflux symptoms and/or esophagitis on endoscopy. Asymptomatic subjects with no endoscopic esophagitis were selected as controls, and the cell counts in this group were used to define the upper limit of normal of IELs, eosinophils and neutrophils. The entire sample was used to identify independent predictors of increased cellular counts by logistic regression analysis. None of the healthy controls had an IEL count of more than three per five high power fields (HPF), and therefore this was considered as the upper limit of normal; no controls had eosinophils or neutrophils in esophageal biopsies. Independent predictors of an elevated IEL count were spongiosis on histology (OR 11.17, 95% CI 3.32-37.58, P < 0.01) and current smoking (OR 4.84, 95% CI 1.13-2.71, P = 0.03). A receiver operating characteristics analysis concluded that a threshold of 3 IELs/5HPFs performs best in predicting reflux symptoms when a normal esophageal mucosa is visualized on endoscopy (sensitivity = 100.0%, specificity = 35.2%). The healthy esophageal mucosa does not contain more than three IELs per five HPF in the distal esophagus.