Estimate of the Prevalence of Anti-Gastric Parietal Cell Autoantibodies in Healthy Individuals Is Method Dependent

Monitoring the follow-up of autoimmune chronic atrophic gastritis using parietal cell antibodies and markers of gastric function

Increased interest in the pathogenesis and the evolution of autoimmune chronic atrophic gastritis (A-CAG) has led to the search for serological markers that can be used to detect changes in the gastric mucosa at an early stage and to monitor the course of the disease. Parietal cell autoantibodies have been proposed as suitable immunological markers of atrophic damage, as they can be detected in the serum when symptoms of gastritis are not yet present. However, the utility of measuring only the level of parietal cell autoantibodies in the follow-up of A-CAG does not appear to suffice. Recent evidence has suggested that, in monitoring A-CAG, parietal cell antibodies should be associated with an evaluation of gastric function through biochemical and hormonal tests, such as pepsinogens and gastrin 17. This integrated approach will allow for the more effective real-time monitoring of the state of the gastric mucosa. As A-CAG is a progressive disorder associated with an increased risk of gastric cancer and neuroendocrine tumors, the precise follow-up of patients with gastric atrophy needs to be better defined. Further longitudinal studies in large cohorts must be performed with long-term follow-up.

Prevalence of Autoantibodies in Patients with Hereditary Alpha-Tryptasemia

INTRODUCTION

Hereditary alpha-tryptasemia (HαT) is associated with postural orthostatic tachycardia syndrome (POTS), hypermobile Ehlers-Danlos syndrome (hEDS), and mast cell activation syndrome (MCAS). While POTS, hEDS, and MCAS have all demonstrated increased prevalence of autoimmunity, this has not been investigated in HαT populations. Our objective was to describe the prevalence of autoantibodies in individuals with HαT.

METHODS

We retrospectively studied a cohort of patients with positive genotyping for HαT at a tertiary-care allergy clinic. Demographic data including previous autoimmune history and autoantibody serologies were extracted on chart review. A literature search was conducted to determine the prevalence of specific autoimmune and autoantibody prevalences in the general population. We compared the proportions of autoantibody positivity and established autoimmune diseases in our cohort of HαT individuals against those in general populations.

RESULTS

We identified 101 patients with HαT. Median age was 43 years (range 15-75), and most were female (87/101; 86.1%). Prevalence of self-reported drug hypersensitivity was 52/101 (52.5%) patients. The proportion of individuals with HαT with positive tTG antibody (3/61, 4.9%) was significantly higher than that reported in the general population (133/16,667, 0.8%) (p < 0.001). The prevalence of systemic lupus erythematosus (SLE) (1/101, 1%) and celiac disease (5/101, 5%) in our cohort were found to be significantly higher than the prevalence in the general population (194/96,996, 0.2% [p = 0.035] and 26/2,845, 0.9% [p < 0.001], respectively).

CONCLUSION

Patients with HαT have increased prevalence of celiac disease, SLE, and positive anti-tTG serology, as well as self-reported drug hypersensitivity, relative to general populations.

Improving the Diagnosis of Autoimmune Gastritis: From Parietal Cell Antibodies to H+/K+ ATPase Antibodies

Parietal cell autoantibodies (PCAs), which recognize the enzyme H+/K+-ATPase as a target, are considered to be a diagnostic marker of autoimmune gastritis and pernicious anemia; these conditions are characterized by the presence of corpus atrophic gastritis. Circulating PCAs can be detected using several analytical methods that are commonly available in the clinical laboratory. Traditionally, indirect immunofluorescence (IIF) on rodent or primate stomach tissue is used as a screening test for the detection of PCAs. However, IIF suffers from a high inter-observer variability and lacks standardization. In addition, like immunoblotting, results are expressed only in a qualitative or semi-quantitative manner. Based on the few available studies that are reviewed herein, quantitative enzyme-linked immunosorbent assays (ELISAs) and fluorescence enzyme immunoassays (FEIAs) using purified H+/K+-ATPase perform better than IIF in the detection of PCAs, displaying higher sensitivity and utility in monitoring the disease. In light of their higher diagnostic accuracy, these solid-phase methods should be preferred to IIF in the screening of autoimmune atrophic gastritis. The use of methods to detect antibodies versus a specific subunit of H+/K+-ATPase (α or β) is currently confined to the world of research. Further investigation is required to define the clinical utility of H+/K+-ATPase subunit detection.

Autoimmune Gastritis and Hypochlorhydria: Known Concepts from a New Perspective

Autoimmune atrophic gastritis is an immune-mediated disease resulting in autoimmune destruction of the specialized acid-producing gastric parietal cells. As a consequence, in autoimmune atrophic gastritis, gastric acid secretion is irreversibly impaired, and the resulting hypochlorhydria leads to the main clinical manifestations and is linked, directly or indirectly, to the long-term neoplastic complications of this disease. In the last few years, autoimmune atrophic gastritis has gained growing interest leading to the acquisition of new knowledge on different aspects of this disorder. Although reliable serological biomarkers are available and gastrointestinal endoscopy techniques have substantially evolved, the diagnosis of autoimmune atrophic gastritis is still affected by a considerable delay and relies on histopathological assessment of gastric biopsies. One of the reasons for the diagnostic delay is that the clinical presentations of autoimmune atrophic gastritis giving rise to clinical suspicion are very different, ranging from hematological to neurological-psychiatric up to gastrointestinal and less commonly to gynecological-obstetric symptoms or signs. Therefore, patients with autoimmune atrophic gastritis often seek advice from physicians of other medical specialties than gastroenterologists, thus underlining the need for increased awareness of this disease in a broad medical and scientific community.

RE.GA.IN.: the Real-world Gastritis Initiative-updating the updates

At the end of the last century, a far-sighted 'working party' held in Sydney, Australia addressed the clinicopathological issues related to gastric inflammatory diseases. A few years later, an international conference held in Houston, Texas, USA critically updated the seminal Sydney classification. In line with these initiatives, Kyoto Global Consensus Report, flanked by the Maastricht-Florence conferences, added new clinical evidence to the gastritis clinicopathological puzzle.The most relevant topics related to the gastric inflammatory diseases have been addressed by the Real-world Gastritis Initiative (RE.GA.IN.), from disease definitions to the clinical diagnosis and prognosis. This paper reports the conclusions of the RE.GA.IN. consensus process, which culminated in Venice in November 2022 after more than 8 months of intense global scientific deliberations. A forum of gastritis scholars from five continents participated in the multidisciplinary RE.GA.IN. consensus. After lively debates on the most controversial aspects of the gastritis spectrum, the RE.GA.IN. Faculty amalgamated complementary knowledge to distil patient-centred, evidence-based statements to assist health professionals in their real-world clinical practice. The sections of this report focus on: the epidemiology of gastritis; Helicobacter pylori as dominant aetiology of environmental gastritis and as the most important determinant of the gastric oncogenetic field; the evolving knowledge on gastric autoimmunity; the clinicopathological relevance of gastric microbiota; the new diagnostic horizons of endoscopy; and the clinical priority of histologically reporting gastritis in terms of staging. The ultimate goal of RE.GA.IN. was and remains the promotion of further improvement in the clinical management of patients with gastritis.

Autoimmune gastritis serological biomarkers in gastric cancer patients

The role of autoimmunity in the pathogenesis of gastric cancer remains controversial. We studied antiparietal cell antibody (anti-PCA) and anti-intrinsic factor antibody (anti-IFA) levels and their associations with pepsinogen I/pepsinogen II levels in patients with gastric adenocarcinoma compared to a control group with mild or no atrophy of the stomach mucosa. Plasma levels of anti-PCA and anti-IFA were measured by ELISA (Inova Diagnostics Inc, San Diego, California, USA). The cutoff value for anti-PCA and anti-IFA positivity was ≥25 units. Altogether 214 patients (126 men, 88 women, median age 64.46, range: 35-86) with confirmed gastric adenocarcinoma and 214 control cases paired for age and sex were included in the study. Positive anti-PCA was present in 22 (10.3%) gastric cancer patients and controls (P ≥ 0.999); positive anti-IFA in 6 (2.8%) and 4 (1.9.%), P < 0.232, respectively. We did not find significant differences in anti-PCA and anti-IFA positivity between gastric cancer patients and the control group; further investigation is required to better understand the potential involvement of autoimmune gastritis in the development of gastric cancer.

Incidence and Predictors of Gastric Neoplastic Lesions in Corpus-Restricted Atrophic Gastritis: A Single-Center Cohort Study

INTRODUCTION

Corpus-restricted atrophic gastritis is a chronic inflammatory disorder leading to possible development of type 1 neuroendocrine tumors (T1gNET), intraepithelial neoplasia (IEN), and gastric cancer (GC). We aimed to assess occurrence and predictors of gastric neoplastic lesions in patients with corpus-restricted atrophic gastritis at long-term follow-up.

METHODS

A prospective single-center cohort of patients with corpus-restricted atrophic gastritis adhering to endoscopic-histological surveillance was considered. Follow-up gastroscopies were scheduled according to the management of epithelial precancerous conditions and lesions of the stomach guidelines. In case of new/worsening of known symptoms, gastroscopy was anticipated. Cox regression analyses and Kaplan-Meier survival curves were obtained.

RESULTS

Two hundred seventy-five patients with corpus-restricted atrophic gastritis (72.0% female, median age 61 [23-84] years) were included. At a median follow-up of 5 (1-17) years, the annual incidence rate person-year was 0.5%, 0.6%, 2.8%, and 3.9% for GC/high-grade IEN, low-grade IEN, T1gNET, and all gastric neoplastic lesions, respectively. All patients showed at baseline operative link for gastritis assessment (OLGA)-2, except 2 low-grade (LG) IEN patients and 1 T1gNET patient with OLGA-1. Age older than 60 years (hazard ratio [HR] 4.7), intestinal metaplasia without pseudopyloric metaplasia (HR 4.3), and pernicious anemia (HR 4.3) were associated with higher risk for GC/HG-IEN or LG-IEN development and shorter mean survival time for progression (13.4, 13.2, and 11.1, respectively, vs 14.7 years, P = 0.01). Pernicious anemia was an independent risk factor for T1gNET (HR 2.2) and associated with a shorter mean survival time for progression (11.7 vs 13.6 years, P = 0.04) as well as severe corpus atrophy (12.8 vs 13.6 years, P = 0.03).

DISCUSSION

Patients with corpus-restricted atrophic gastritis are at increased risk for GC and T1gNET despite low-risk OLGA scores, and those aged older than 60 years with corpus intestinal metaplasia or pernicious anemia seem to display a high-risk scenario.

Update on Serum Biomarkers in Autoimmune Atrophic Gastritis

BACKGROUND

Autoimmune atrophic gastritis (AAG) is a persistent, corpus-restricted immune-mediated destruction of the gastric corpus oxyntic mucosa with reduced gastric acid and intrinsic factor secretion, leading to iron deficiency and pernicious anemia as a consequence of iron and cobalamin malabsorption. Positivity toward parietal cell (PCA) and intrinsic factor (IFA) autoantibodies is very common. AAG may remain asymptomatic for many years, thus making its diagnosis complex and often delayed. Due to the increased risk of gastric neoplasms, a timely diagnosis of AAG is clinically important.

CONTENT

The gold standard for AAG diagnosis is histopathological assessment of gastric biopsies obtained during gastroscopy, but noninvasive, preendoscopic serological screening may be useful in some clinical scenarios. Serum biomarkers for AAG may be divided into 2 groups: gastric autoimmunity-related biomarkers, such as PCA and IFA, and gastric corpus atrophy/reduced gastric acid secretion-related biomarkers, such as serum gastrin and pepsinogens. The present review focuses on the clinical significance and pitfalls of serum biomarkers related to gastric autoimmunity and gastric corpus atrophy, including some discussion of analytical methods.

SUMMARY

Serum assays for PCA, IFA, gastrin, and pepsinogen I show good diagnostic accuracy for noninvasive diagnostic work-up of AAG. Diagnostic performance may increase by combining >1 of these tests, overcoming the problem of seronegative AAG. However, appropriately designed, comparative studies with well-characterized patient cohorts are needed to better define the reliability of these biomarkers in the diagnosis of patients with AAG. Currently, positive serum tests should always be followed by the state-of-art diagnostic test, that is, histopathological assessment of gastric biopsies obtained during gastroscopy to definitively confirm or rule out AAG and eventually neoplastic complications.

Autoimmune Gastritis with a Long-term Course of Type B Gastritis: A Report of Two Cases

Autoimmune gastritis (AIG) typically exhibits the characteristics of type A gastritis and has been classified as a separate disease from type B gastritis that corresponds to Helicobacter pylori gastritis. However, many reports have suggested the involvement of H. pylori infection in the pathogenesis of AIG. In our two cases, the patients' previous gastritis exhibited a clear pattern in which H. pylori gastritis had progressed over many years, but ultimately transitioned to AIG with its spontaneous disappearance. These findings suggest that some cases of AIG might originate from long-standing H. pylori gastritis.

The Diagnostic Value of Anti-Parietal Cell and Intrinsic Factor Antibodies, Pepsinogens, and Gastrin-17 in Corpus-Restricted Atrophic Gastritis

We aimed to determine the diagnostic value of anti-parietal cell antibodies (anti-PCA), anti-intrinsic factor antibodies (anti-IFA), pepsinogen ratio (PGI/II), and gastrin-17 (G-17) in corpus-restricted atrophic gastritis (CRAG) detected by ELISA (Inova, Biohit). Our study compared 29 CRAG cases against 58 age- and sex-matched controls with mild or no atrophy. Anti-PCA and anti-IFA positive cutoff values were ≥25 units for both. PGI/II value <3 was considered characteristic for atrophy; positive cutoff values for G-17 and anti-H. pylori IgG were >5 pg/L and >30 EIU. Anti-PCA was positive in 65.5% For CRAG cases and 13.8% of the controls (p < 0.0001), anti-IFA was positive in 13.8% and 0% (p = 0.01), respectively. Decreased pepsinogen levels were present in 79.3% of CRAG cases and 10.3% of the controls (p < 0.0001). PGI/II ratio was the best single biomarker, with sensitivity = 79%, specificity = 90%, and AUC 0.90. The combined use of PGI/II and anti-PCA resulted in AUC 0.93 for detecting CRAG. Our study suggests that the best combination of non-invasive biomarkers for detecting CRAG is PGI/II with anti-PCA. The addition of G-17 and anti-IFA is of little utility in clinical application.

Intrinsic factor autoantibodies by luminescent immuno-precipitation system in patients with corpus atrophic gastritis

Background

Corpus atrophic gastritis (CAG) may lead to intrinsic factor (IF) deficiency and vitamin B₁₂ malabsorption. Intrinsic factor autoantibodies (IFA) are considered markers of pernicious anemia, but their clinical utility in CAG has not been evaluated. This study aimed to assess IFA in CAG patients and controls using a luciferase immunoprecipitation system (LIPS).

Methods

Recombinant nanoluciferase-tagged IF secreted from transfected Expi293F cells was used as antigen in an IFA-LIPS assay. IFA IgG were measured in sera from subjects undergoing gastroscopy and biopsy (updated Sydney system) mainly for anemia (57%) or dyspepsia (34%). This cohort comprised 105 patients with histologically-proven-CAG (cases: median age 64 years, 68% females) and 110 subjects with suspected CAG that were histologically negative (controls: median age 67 years, 54% females). Cut-off values were selected by Q-Q-plot analysis (negative: <2.5 arbitrary units).

Results

IFA levels were higher in cases than in controls (Mann-Whitney:p < 10⁻⁵). The ROC-AUC was 0.67 (95%CI 0.60–0.73, p < 0.0001). The IFA LIPS sensitivity and specificity for CAG were 32% (95% CI 24–42) and 95% (95% CI 90–99). This diagnostic performance remained similar after stratification for the presence/absence of anemia, dyspepsia or vitamin B₁₂ deficiency. IFA levels were higher in females compared with males (p = 0.0127). In females aged <65 years, IFA-positives were more prevalent than in males (43.5% vs 6.6%, p = 0.011).

Conclusions

The IFA-LIPS assay discriminated between CAG patients and controls showing a good specificity (95%) at the cost of sensitivity (32%). IFA-positivity occurred independently from anemia and vitamin B₁₂ deficiency, but was more frequent in younger females. IFA testing should be considered in patients at high clinical suspicion of CAG.

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A novel diagnostic autoantibody test for intrinsic factor autoantibodies using a LIPS in histologically-proven CAG patients and controls.

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This assay discriminated between patients and controls with a good specificity and a relatively low sensitivity that reflects the likely low prevalence of intrinsic factor antibodies in CAG.

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Positivity occurred independently from anemia and vitamin B₁₂ deficiency.

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Intrinsic factor antibodies should be assessed in patients at high clinical suspicion of CAG.

Screening of Organ-Specific Autoantibodies in a Large Cohort of Patients with Autoimmune Thyroid Diseases

Background: Autoimmune diseases tend to cluster in the same individual or in families. Four types of autoimmune polyglandular syndromes (APS) have been described based on the combination of endocrine and/or non-endocrine autoimmune diseases. In particular, type-3 APS is defined by the association of an autoimmune thyroid disease (ATD) and other autoimmune diseases and has a multifactorial etiology. The natural history of autoimmune diseases is characterized by three stages: potential, subclinical, and clinical. Methods: To determine the prevalence of organ-specific autoantibodies (anti-adrenal, anti-ovary [StCA], anti-pituitary [APA], anti-parietal cells [PCA], anti-tissue transglutaminase [tTGAb], anti-mitochondrial [AMA], anti-glutamic acid decarboxylase [GADA], anti-nicotinic acetylcholine receptor) in patients with ATD and to define the stage of the disease in patients with positive autoantibodies. From January 2016 to November 2018, 1502 patients (1302 female; age 52.7 ± 14.7 [mean ± standard deviation] years, range 18-86 years) with ATD (1285/1502 [85.6%] with chronic autoimmune thyroiditis and 217/1502 [14.4%] with Graves' disease) were prospectively enrolled. Results: The most common organ-specific autoantibodies were PCA (6.99%) and GADA (2.83%), while the prevalence of the remaining autoantibodies was ≤1%. All autoimmune diseases, but celiac disease, were predominant at the potential stage. Sex, ATD type, smoking habit, and coexistence of other autoimmune diseases correlated with the susceptibility to develop chronic atrophic gastritis (CAG) or autoimmune diabetes mellitus. Conclusions: The association between ATD and CAG was the most common manifestation of type-3 APS, mainly at the potential stage, that could lead to appropriate follow-up for early detection and timely treatment of the disease.

Seronegative autoimmune atrophic gastritis is more common in elderly patients

BACKGROUND

Autoimmune atrophic gastritis (AAG) diagnosis is based on specific histological findings and anti-parietal cell antibodies (PCA) considered the serological hallmark of AAG, although a subgroup of AAG patients may be seronegative.

OBJECTIVES

To assess the occurrence and clinical features of seronegative compared to seropositive AAG.

METHODS

This is a cross-sectional study including 516 consecutive adult patients (age 59.6 ± 12.8 years, F:M = 2.2:1) with histologically proven AAG diagnosed in two Italian academic referral centers over the last 10 years. PCA were detected at AAG diagnosis. Variables related to the dependent variable of interest (i.e.PCA-negativity) were assessed by univariate/logistic regression analysis.

RESULTS

109/516 AAG patients were seronegative. The mean age of seronegative AAG patients was significantly higher compared to PCA-positive (65.9 ± 14.1vs57.9 ± 15.1 years; p<0.0001). The proportion of patients aged 70-79 and ≥80 years were, respectively, lower for PCA-positivity (5.1vs12.8%;21.3vs38.5%;p<0.005). Seronegativity was associated with age ≥50 years (OR2.4;95%CI 1.1-5.2), while for other variables (gender, comorbidities, anemia, atrophy severity) no association was found. In a sub-cohort of 101 AAG patients, PCA levels detected by ELISA were inversely correlated with age at AAG diagnosis (rho=-0.250;p = 0.0118).

CONCLUSION

Roughly 20% of patients are seronegative at the time of AAG histological diagnosis and this is more common in elderly individuals.

Autoantibodies Toward ATP4A and ATP4B Subunits of Gastric Proton Pump H+,K+-ATPase Are Reliable Serological Pre-endoscopic Markers of Corpus Atrophic Gastritis

INTRODUCTION

Noninvasive assessment of corpus atrophic gastritis (CAG), a condition at increased risk of gastric cancer, is based on the measurement of pepsinogens, gastrin, and Helicobacter pylori antibodies. Parietal cell autoantibodies (PCAs) against the gastric proton pump (ATP4) are potential serological biomarkers of CAG. The purpose of this study was to compare the diagnostic performance of PCA and pepsinogen I tests in patients with clinical suspicion of CAG with the histopathological evaluation of gastric biopsies as reference standard.

METHODS

A prospective case-finding study was performed on 218 naive adult patients (131 women, median age 65 years) who underwent gastric biopsies to confirm/exclude CAG. Patients with histopathological CAG were defined as cases, conversely as controls. Autoantibodies against the individual alpha (ATP4A) and beta (ATP4B) subunits of ATP4 were measured by luciferase immunoprecipitation, and global PCA and pepsinogen I by enzyme-linked immunosorbent assay.

RESULTS

Histopathology classified 107 subjects (49%) as cases (CAG+, autoimmune 81.2%, and multifocal extensive 18.8%) and 111 subjects (51%) as controls (CAG-). In cases, ATP4A, ATP4B, and PCA titers were increased compared with controls, whereas pepsinogen I was reduced (P < 0.0001 for all). ATP4B, ATP4A, and pepsinogen I tests showed sensitivities of 77%, 75%, and 73% and specificities of 88%, 88%, and 80%, respectively. The receiver operating characteristic (ROC) area under the ROC curve (AUC) of these serological biomarkers confirmed their ability to discriminate cases from controls (ATP4B = 0.838, ATP4A = 0.826, pepsinogen I = 0.775, and PCA = 0.805), whereas the partial ROC-pAUC90 analysis showed that the ATP4B test had the best diagnostic performance (P = 0.008 vs ATP4; P = 0.0002 vs pepsinogen I). The presence of autoimmune or extensive gastritis was not significantly different between ATP4B positive or negative cases (P = 0.217).

DISCUSSION

PCAs are promising serological biomarkers for the identification of CAG in high-risk individuals, particularly in an autoimmune pattern but also in an extensive-multifocal atrophy pattern.

Comparison of different immunoassays for the detection of antibodies against Intrinsic Factor and Parietal Cells

OBJECTIVES

In the diagnostic work up of autoimmune gastritis several immunological methods are available for the detection of antibodies against Intrinsic Factor (IF) and Parietal Cells (PC). However, there are no recent reports directly comparing all the available assays and methods. The objective of this study was to compare the performance of several commercially available anti-IF and anti-PC antibody assays from different manufacturers in a multi-center multi-cohort setting.

METHODS

Sera were used from 5 different cohorts consisting of samples from 25 healthy elderly, 20 HCV or HIV positive patients and 150 patients positive for anti-IF or anti-PC antibodies or in whom these antibodies were requested. These cohorts were tested for anti-IF antibodies with 6 different assays (IIF, ELISA, DIA and EliA) and for anti-PC antibodies with 7 different assays (IIF, ELISA, DIA and EliA). Performance was evaluated by calculating the concordance and relative sensitivity and specificity.

RESULTS

Good concordance was found between the assays for both antibody specificities, ranging from 81 to 100% and 91-100% for anti-IF and anti-PC antibodies, respectively. Highest relative sensitivity was found with the (automated) ELISA based methods. However, all assays had a relative sensitivity between 85 and 100% for anti-IF antibodies and between 95 and 100% for anti-PC antibodies. The relative specificity ranged between 76 and 100% for anti-IF antibodies and between 96 and 100% for anti-PC antibodies.

CONCLUSIONS

We conclude that most assays perform well and are concordant to each other, despite the methodological differences and the different sources of antigen used. However, the method used affects the sensitivity and specificity. The (automated) ELISA based assays have the highest relative sensitivity and relative specificity. Care should be taken in the interpretation of positive results by IIF and negative results by the Blue Diver when testing for anti-IF antibodies.

Autoimmune gastritis

Autoimmune gastritis (AIG) is an increasingly prevalent, organ-specific, immune-mediated disorder characterized by the destruction of gastric parietal cells, leading to the loss of intrinsic factor and reduced acid output. These alterations result in malabsorption of iron, vitamin B₁₂ (pernicious anaemia) and potentially other micronutrients. For several years, most studies have focused on pernicious anaemia only, generating confusion between the two entities. In AIG, the gastric proton pump, H⁺/K⁺ ATPase, is the major autoantigen recognized by autoreactive T cells. The T cell-dependent activation of B cells stimulates the production of anti-parietal cell antibodies, the serological hallmark of AIG. The role of Helicobacter pylori infection in activating or favouring the autoimmune process is still uncertain. Early histopathological alterations allowing a more precise and prompt recognition have recently been described. AIG is burdened by a substantial diagnostic delay as it can present with varied clinical signs including, among others, gastrointestinal symptoms and neuropsychiatric manifestations. In advanced stages, AIG might progress to neuroendocrine tumours and gastric adenocarcinoma. Management includes early detection through a proactive case-finding strategy, micronutrient supplementation and endoscopic surveillance. This Primer comprehensively describes the most important insights regarding the epidemiology, pathophysiology, diagnosis and management of AIG, focusing on the most controversial, outstanding issues and future directions.

Thyro-entero-gastric autoimmunity: Pathophysiology and implications for patient management

The association between autoimmune atrophic gastritis and thyroid disorders has been observed since the early 1960s and the expression "thyrogastric syndrome" was coined to indicate the presence of thyroid autoantibodies or autoimmune thyroid disease in patients with pernicious anemia, a late clinical stage of autoimmune atrophic gastritis. More recently, it was confirmed that autoimmune thyroid disorders, in particular Hashimoto's thyroiditis, may be frequently associated with other organ-specific, immune-mediated disorders, such as autoimmune atrophic gastritis or celiac disease. The association of Hashimoto's thyroiditis with autoimmune atrophic gastritis or celiac disease in adult patients is currently considered part of the polyglandular autoimmune syndromes which include several autoimmune disorders associated with an autoaggressive impairment of endocrine glands. From a clinical point of view, the thyro-entero-gastric autoimmunity may lead to potentially serious consequences like anemia, micronutrients deficiencies, and drugs malabsorption, as well as to an increased risk for malignancies. These alterations may frequently present in an underhand manner, with consequent diagnostic and treatment delays. Many aspects of the association between thyroid, gastric and intestinal autoimmune diseases still await clarification. The present review focuses on the embryological, genetic and pathophysiological aspects of thyro-entero-gastric autoimmunity. In particular, the current diagnostic criteria of autoimmune thyroid disease, autoimmune atrophic gastritis, and celiac disease are reviewed, along with the evidences for their association in poly-autoimmunity syndromes. The benefits of proactive screening of autoimmune thyroid disorders in patients with autoimmune gastritis or enteropathy and viceversa are also discussed.