Mucosal and systemic IgA anti-gliadin antibody in celiac disease. Contrasting patterns of response in serum, saliva, and intestinal secretions

Correlation of Celiac Diseases with Candida Spp. Based on Anti-gliadin Antibodies

A variety of Candida spp. can be found as a natural commensal fungus in various parts of the human body. This fungus may be associated with various diseases such as celiac disease (CD). Gliadin, a component of the gluten protein complex that is mostly found in wheat, is the main inducer of CD. A number of studies have demonstrated that patients infected with Candida can develop CD, and vice versa. C. albicansis presumed to induce CD because it has a protein homologous to gliadin in its cell wall called Hwp1. Despite the non-specificity of the anti-gliadin test, the detection of antibodies against anti-gliadin (AGA) and anti-tissue transglutaminase (anti-tTG) are important in the diagnosis of CD. Some evidence is now available to support the hypothetical correlation between Candida spp. and CD, as high levels of AGA have been found in patients infected with candidiasis without CD. Further study is needed to confirm this relationship.

A Life in Food: A Grain of Salt and Some Humble Pie

From my senior school days, I had wanted to pursue a career in food. In quite what capacity I was not too sure. So my starting points were within the fields of animal nutrition before moving for the major part of my career to medical schools to study human nutrition and health. My career scientific achievements lie within the Kuhnian spectrum of normal science, but within that normality, I was always one to challenge conventional wisdom. An academic career is about more than just research. It is about teaching and not just the minutiae of nutrition, but about life and living, about challenges and failures. Reflecting on the experience of that career, my advice to early stage researchers is this: Be patient, determined, and resilient in the very early stages. Hold no fear of change and be courageous in challenging conventional wisdom. Always favor openness and collaboration and always seek to help others. Citation indices are important to your career, but these other avenues that I advise you to follow are what you will eventually be most proud of.

Diet and psoriasis, part II: celiac disease and role of a gluten-free diet

Patients with psoriasis have been shown to have a higher prevalence of other autoimmune diseases including celiac disease, a condition marked by sensitivity to dietary gluten. A number of studies suggest that psoriasis and celiac disease share common genetic and inflammatory pathways. Here we review the epidemiologic association between psoriasis and celiac disease and perform a meta-analysis to determine whether patients with psoriasis more frequently harbor serologic markers of celiac disease. We also examine whether a gluten-free diet can improve psoriatic skin disease.

Selected disorders of malabsorption

Malabsorption syndrome encompasses numerous clinical entities that result in chronic diarrhea, abdominal distention, and failure to thrive. These disorders may be congenital or acquired and include cystic fibrosis and Shwachman-Diamond syndrome; the rare congenital lactase deficiency; glucose-galactose malabsorption; sucrase-isomaltase deficiency; adult-type hypolactasia leading to acquired lactose intolerance. The pathology may be due to impairment in absorption or digestion of nutrients resulting in Nutritional deficiency, gastrointestinal symptoms, and extra gastrointestinal symptoms. Treatment is aimed at correcting the deficiencies and symptoms to improve quality of life. Common disorders of malabsorption celiac disease, pernicious anemia, and lactase deficiency are discussed in this article.

Two-year follow-up of anti-transglutaminase autoantibodies among celiac children on gluten-free diet: Comparison of IgG and IgA

OBJECTIVES

To investigate the evolution of IgA and IgG autoantibodies against tissue transglutaminase (tTGase) in celiac patients on gluten-free diet (GFD).

METHODS

IgA and IgG anti-tTGAse autoantibodies was evaluated in 93 patients (58 girls and 35 boys; mean age 3.56 +/- 3.04 years; range 0.94-17.5 years) at diagnosis of celiac disease and after 1, 2, 4, 6, 12, 18, 24 months of follow-up on GFD. Autoantibodies were measured with a radioassay using in vitro transcribed-translated human recombinant tTGAse, and immune complexes were precipitated with protein A- or anti-IgA-agarose for IgG and IgA, respectively.

RESULTS

Autoantibody titers started to decline very soon after removal of gluten, and no significant differences in the decrease rate between IgG and IgA antibodies were observed. After 6 months on GFD, 63 and 49% of the patients were negative for IgG and IgA, respectively. Patients who remained autoantibody-positive after 6 months of treatment initially presented with significantly higher titers at the time of diagnosis compared to patients that had lost their antibodies by that time. Children diagnosed before the age of two years presented lower autoantibody titers, while patients positive for HLA-DR7 had higher anti-tTGase levels, especially IgA.

CONCLUSIONS

There are no differences in the performance of IgG and IgA class autoantibodies in the evolution of celiac patients. Between 3 and 6 months on GFD, almost half of the patients are negative for anti-tTGase antibodies. In our experience, they can be of help in evaluating compliance with diet, at least during the first two years of treatment.

Symposium on 'The challenge of translating nutrition research into public health nutrition'. Session 3: Joint Nutrition Society and Irish Nutrition and Dietetic Institute Symposium on 'Nutrition and autoimmune disease'. Recent advances in genetic understanding of coeliac disease

Over the past 20 years major advances have been made in the diagnosis and understanding of pathogenic mechanisms relating to coeliac disease. Recently-identified genetic markers support the immunological-inflammatory nature of the disease. It is hoped that these newly-identified genes will assist further dissection of the inflammatory pathways in coeliac disease and give insight into why certain individuals develop intolerance to dietary gluten.

Orally based diagnosis of celiac disease: current perspectives

Celiac disease (CD) is a lifelong immune-mediated disorder caused by the ingestion of wheat gluten in genetically susceptible persons. Most cases of CD are atypical and remain undiagnosed, which exposes the individuals to the risk of life-threatening complications. Serologic endomysial and tissue transglutaminase antibody tests are used to screen at-risk individuals, although a firm diagnosis requires demonstration of characteristic histopathologic findings in the small-intestinal mucosa. A gluten challenge, with a repeat biopsy to demonstrate recurrence of histopathologic changes in the intestinal mucosa after the re-introduction of gluten, is considered for those persons in whom diagnosis remains in doubt. In this paper, we review studies that evaluated: (1) the possibility of using oral mucosa for the initial diagnosis of CD or for local gluten challenge; and (2) the possibility of using salivary CD-associated antibodies as screening tests. Our review shows that orally based diagnosis of CD is attractive and promising, although additional evaluations with standardized collection and analysis methods are needed. There is some evidence of a dissociation between systemic and oral mucosal immune responses in CD. The hypothesis that gluten could stimulate naive lymphocytes directly in the oral cavity would have important implications for the understanding, diagnosis, and management of CD.

Recent advances in the understanding of celiac disease: therapeutic implications for the management of pediatric patients

Celiac disease (CD) is an autoimmune condition occurring in genetically susceptible individuals characterized by inflammatory injury to the mucosa of the small intestine after the ingestion of wheat glutens or related barley and rye products. Originally thought to be highly prevalent only in Northern European populations, growing evidence indicates a much higher prevalence in many other regions, including the US as well as South America, North Africa, and Asia. The growing awareness that pediatric patients may present with quite diverse and protean manifestations and the significant impact of CD on childhood development has prompted efforts to increase CD awareness for the early diagnosis and treatment of this disease. The current diagnostic criteria for CD requires characteristic histologic findings in small bowel biopsies and clinical remission when placed on a gluten-free diet. Serologic testing for CD can provide additional support for the diagnosis of CD or a means to assess efficacy and adherence to a gluten-free diet. The mainstay of treatment remains the institution of a gluten-free diet. However, patients with refractory CD may require treatment with immunosuppressant medications. With the increased identification of specific gluten epitopes and understanding of the pathogenesis of CD, future therapies may rely on genetically altering gluten proteins, immunization techniques, or therapies focused on either the development of specific immune tolerance or regulation of mucosal inflammation.

Serum levels of soluble CD163 correlate with the inflammatory process in coeliac disease

BACKGROUND

In coeliac disease, following the introduction of a gluten-free diet, monitoring mucosal disease activity requires repeated small intestinal biopsies. If a test measuring a circulating inflammatory marker was available, this would be clinically valuable.

AIM

To determine if levels of soluble CD163, a scavenger receptor shed by tissue macrophages, correlated with the inflammatory lesion in coeliac disease.

METHODS

Serum samples were collected from 131 patients with untreated coeliac disease, 40 patients with treated coeliac disease, 92 non-coeliac disease control subjects and 131 healthy controls. A capture enzyme linked immunosorbance assay was established to measure levels of soluble CD163 in sera. The extent of the histological lesion in coeliac biopsies was assessed using a Marsh grading system.

RESULTS

Levels of CD163 in untreated coeliac subjects were significantly elevated when compared with the treated coeliac patients, the disease control group and the healthy control subjects (P < 0.0001 in each instance). Moreover, coeliac patients with the most marked histological lesion (Marsh 3) had significantly higher levels of soluble CD163 than patients with Marsh grade 2 lesions (P < 0.0004), with grade 1 lesions (P < 0.0001) and grade 0 lesions (P < 0.0001).

CONCLUSIONS

Measurement of soluble CD163 may be a useful method of monitoring the inflammatory lesion in coeliac disease.

Tissue transglutaminase autoantibody detection in human saliva: a powerful method for celiac disease screening

OBJECTIVE

To test the possibility of detecting tissue transglutaminase autoantibodies (tTG-Abs) in saliva with a novel sensitive fluid-phase radioimmunoassay (RIA).

STUDY DESIGN

Paired saliva and serum samples from 39 patients with celiac disease (CD), at the first biopsy (Group 1: 28 females, mean age 11.5 +/- 11.1 years); 32 controls with a normal duodenal mucosa (Group 2: 18 females, mean age 8.1 +/- 3.6 years); and 32 healthy volunteers (Group 3: 21 females, mean age 31.7 +/- 9.8 years) were studied for tTG-Ab presence. Limit of positivity for salivary assay was calculated according to the 99th percentiles of Group 2 control children and was expressed as an autoantibody (Ab) index.

RESULTS

Salivary tTG-Abs were found in 97.4% of the patients with CD and in 100% of the corresponding serum samples. All Group 3 subjects were negative with both saliva and serum assays. A correlation between saliva and serum tTG-Ab titers was found (r=0.826, P=.0014).

CONCLUSIONS

This study demonstrates that it is possible to detect salivary tTG-Abs in CD with a non-invasive, simple to perform, reproducible and sensitive method.

La maladie cœliaque de l’adulte : aspects nouveaux

INTRODUCTION

Celiac disease also known as gluten-sensitive enteropathy is a complex disorder where genetically susceptible individuals develop in typical cases signs of malabsorption after ingestion of cereals. Malabsorption is due to total or subtotal atrophy of the small intestinal mucosa regressing after adherence to a gluten-free diet. The only effective therapy is life-long strict abstinence from wheat, rye and barley.

CURRENT KNOWLEDGE AND KEY POINTS

During the last two decades spectrum of clinical features of adult celiac disease has been modified. About 60% of cases are now revealed by extraintestinal manifestations. Moreover, recent studies that used serological methods revealed existence of both latent and silent celiac sprue. The finding of the high frequency of atypical celiac sprue contributed to underestimation of the true prevalence of celiac disease until now, and explained that celiac disease could be unknown for a long time, with increased risk of nutritional deficiencies and malignancy. Concurrently, the finding that celiac disease is primarily associated to a few HLA class II molecules, and recent advent of tissue transglutaminase as the main auto-antigen eliciting anti-endomysial antibodies allowed to propose new pathogenesis hypothesis and efficient screening tests for celiac disease diagnosis.

FUTURE PROSPECTS AND PROJECTS

New epidemiological data concerning adult celiac disease must incite to a more systematic screening in patients with atypical but evocative features, or in at-risk subjects. Introduction of enzyme linked immunosorbent assays (ELISA) for the detection for anti-tissue transglutaminase antibodies allows to make use of a new available and efficient diagnosis parameter, which could constitute the main screening test in the near future.

Diagnosis of celiac sprue

Celiac sprue is a common lifelong disorder affecting 0.3-1% of the Western world and causing considerable ill health and increased mortality, particularly from lymphoma and other malignancies. Although high prevalence rates have been reported in Western Europe, celiac sprue remains a rare diagnosis in North America. Whether celiac sprue is truly rare among North Americans or is simply underdiagnosed is unclear, although serological screening of healthy American blood donors suggests that a large number of American celiacs go undiagnosed. Celiac sprue is an elusive diagnosis, and often its only clue is the presence of iron or folate deficiency anemia or extraintestinal manifestations, such as osteoporosis, infertility, and neurological disturbances. The challenge for gastroenterologists and other physicians is to identify the large population of undiagnosed patients that probably exists in the community and offer them treatment with a gluten-free diet that will restore the great majority to full health and prevent the development of complications. The advent of highly sensitive and specific antiendomysium and tissue transglutaminase serological tests has modified our current approach to diagnosis and made fecal fat and D-xylose absorption testing obsolete. A single small bowel biopsy that demonstrates histological findings compatible with celiac sprue followed by a favorable clinical and serological response to gluten-free diet is now considered sufficient to definitely confirm the diagnosis. We review the wide spectrum of celiac sprue, its variable clinical manifestations, and the current approach to diagnosis.

Dissociation of allergen-specific IgE and IgA responses in sera and tears of pollen-allergic patients: a study performed with purified recombinant pollen allergens

BACKGROUND

Trees and grass pollen allergens represent potent elicitors of allergic rhinoconjunctivitis and asthma. Little is known regarding the presence of allergen-specific IgA antibodies in sera and tears and their association with IgE responses in patients with allergic conjunctivitis.

OBJECTIVE

The purpose of this study was to compare the specificities of IgE and IgA antibodies in sera and tears of pollen-allergic patients with conjunctivitis by using purified recombinant pollen allergens.

METHODS

Sera and tears collected from 23 pollen-allergic and from 23 nonatopic individuals were analyzed for IgE and IgA reactivity to nitrocellulose-blotted birch and timothy grass pollen extracts. In addition, we determined the specificities of IgE, IgG(1-4), and IgA antibodies with use of a panel of purified recombinant pollen allergens (timothy grass: rPhl p 1, rPhl p 2, rPhl p 5; birch: rBet v 1, rBet v 2) in serum and tear samples by immunoblotting and ELISA. Statistical analyses of data were performed by t test and Mann Whitney U test.

RESULTS

Serum and tears of many of the pollen-allergic individuals with conjunctivitis exhibited specificity for the very same pollen allergens. No allergen-specific IgE antibodies were detected in tears of nonatopic individuals. IgA antibodies in sera and tears of patients with allergic conjunctivitis were mainly directed against nonallergenic moieties and showed specificities that were significantly different from those of IgE antibodies.

CONCLUSION

The dissociation of IgE and IgA responses and the lack of allergen-specific IgA antibodies in mucosal secretions (eg, tears) may contribute to allergic manifestations in target organs of atopy. Induction of allergen-specific IgA antibodies may hence be considered as a promising strategy for the treatment of mucosal forms of atopy.

Salivary antigliadin and antiendomysium antibodies in coeliac disease

The definitive diagnosis of coeliac disease is based on typical changes in the small intestine biopsy specimens. To screen individuals for coeliac disease serum IgA and IgG antigliadin (AGA), IgA antireticulin (ARA) and IgA antiendomysium (EmA) antibodies are used. The aim of this study was to investigate whether these antibodies can also be detected in saliva as diagnostic markers of coeliac disease. The study population comprised 30 patients with coeliac disease treated with a gluten-free diet, 14 patients with untreated coeliac disease and 13 healthy control subjects. Sera and saliva were tested simultaneously for the presence of IgA and IgG AGA and IgA EmA. None of patients studied had a selective IgA deficiency. There was no significant difference in salivary IgA AGA levels between the three groups tested and there was no correlation between the individual serum and salivary values of IgA AGA. Salivary IgG AGA levels were very low or undetectable. Serum IgA AGA showed a low sensitivity (36.4%) to detect an untreated patient with coeliac disease. All salivary samples, regardless of the study group were negative for IgA EmA. Serum IgA EmAs were universally detected in the sera of patients with newly diagnosed coeliac disease and also in the sera of five of 30 patients with treated coeliac disease. No IgA EmA was detected in the sera of controls. None of the patients studied had a selective IgA deficiency either. Serum IgA EmA is the most sensitive, and IgA and IgG AGA are good indicators for coeliac disease, but salivary IgA or IgG AGA and salivary IgA EmA are not helpful for the diagnosis or follow-up of coeliac disease patients.

Coeliac disease in adults: variations on a theme

In childhood, coeliac disease (gluten enteropathy) tends to show itself with failure to thrive and growth retardation; in adult life with malabsorption syndromes. We report six cases in adults who presented atypically, with features including clotting disorder, hypoglycaemia, weight loss, anaemia and angina pectoris, all of which responded to gluten withdrawal.

Salivary SIgA and SIgA 1 in coeliac disease, inflammatory bowel disease and controls

Levels of secretory IgA1 (SIgA1) in the saliva have not been measured previously in either coeliac disease (CD) or inflammatory bowel disease (IBD). Saliva was collected from coeliacs, IBD patients and controls. The concentration of total SIgA in saliva was measured by enzyme linked immunosorbent assay (ELISA) with an anti-human SIgA antibody as the bound phase and human SIgA isolated from colostrum as the standard. The concentration of SIgA1 was determined using an ELISA with a lectin with a high affinity for human SIgA1. The IBD patients have a significantly higher concentration of SIgA1 than the controls. The rate of secretion of saliva and %SIgA1 was significantly lower in coeliacs than in the control and IBD groups. The rate of secretion of SIgA1 was significantly higher in the IBD than in the coeliacs. We describe hitherto unreported levels of SIgA1 in CD and IBD.

Is small bowel biopsy necessary in adults with suspected celiac disease and IgA anti-endomysium antibodies? 100% positive predictive value for celiac disease in adults

The comparative diagnostic value of IgA anti-endomysium and IgA antigliadin antibodies in adults with histologically confirmed celiac disease is reported. Sera from 144 adult patients (without concurrent dermatitis herpetiformis or IgA deficiency) who underwent small bowel biopsy were analyzed for both IgA anti-endomysium and IgA anti-gliadin antibodies. Nineteen patients (13%) had celiac disease. The presence of IgA antiendomysium antibodies had a sensitivity of 74% and a specificity of 100%. The positive and negative predictive values were 100% and 96%, respectively, and the diagnostic accuracy was 97%. In contrast, IgA anti-gliadin antibodies had positive and negative predictive values of 28% and 96%, respectively, with a diagnostic accuracy of 71%. Based on these data, we suggest that small bowel biopsy is not necessary to diagnose celiac disease in symptomatic adults with IgA antiendomysium antibodies. Due to a negative predictive value of 96%, some symptomatic adults lacking anti-endomysium antibodies will not be correctly diagnosed without small bowel biopsy.

Salivary and serum IgA antigliadin antibodies in dermatitis herpetiformis

Serum IgA class antigliadin antibodies (IgA-AGA) are increased in untreated patients with coeliac disease and dermatitis herpetiformis (DH), and it has been suggested that salivary IgA-AGA measurements could be used as a non-invasive screening test for gluten-sensitive enteropathy. In the present study salivary and serum IgA-AGA were measured by an ELISA test in 10 untreated patients with DH. The results were compared to IgA-AGA levels in nine patients with DH on a long-term gluten-free diet (GFD) and in 20 healthy control subjects on an ordinary diet. The mean serum but not salivary IgA-AGA concentrations were significantly higher in the untreated than in the patients with DH on a long-term GFD. When the 10 untreated patients with DH adhered to a GFD for 3 months, the rash disappeared and the mean serum IgA-AGA decreased to normal levels, but no change was found in the mean salivary IgA-AGA concentration. These results show that serum but not salivary IgA-AGA measurements are suitable for monitoring GFD treatment in patients with DH. The discrepancy between the serum and salivary IgA-AGA concentrations suggests that systemic and salivary IgA-AGA responses are controlled separately.

IgM, IgA, IgG1 and IgG2 specific responses in blood and gut secretion of calves fed soyabean products

Calves fed soya proteins may develop severe gastrointestinal disorders. Whether these are predominantly associated with particular Ig subclasses and (or) dietary proteins remains unclear. Therefore, antibody responses to soyabean protein were analysed by dot- and blot-immunobinding in plasma and intestinal mucous secretions. One-month-old calves were fed for 2.5 months liquid diets based on skim milk powder (SMP) or a mixture (2:3, protein basis) of whey and soyabean products including a low antigenic hydrolysed soya protein isolate (HSPI) and a highly antigenic heated soya flour (HSF). Specific antibodies (Abs) of the main isotypes (IgM, IgA, IgG1, IgG2) were characterised by immunostaining of samples which had been previously incubated with nitrocellulose sheets coated with SMP, HSPI or HSF extracts. Plasma collected before feeding experimental diets showed very little specific Abs. By contrast, 2.5 months later, a three-fold increase (P < 0.05) in IgG1 and IgA titres against HSF antigens was observed in calves fed HSF compared with those fed the control or HSPI diet. IgG1 immunoblotting revealed many protein bands from soya in the molecular range of 22-32 and 38-42 kDa. Immunorecognition of specific proteins from SMP and HSPI remained low and similar among animal groups. Specific IgM, IgA and IgG1 titres against HSF, and to a lesser extent HSPI, were significantly higher (P < 0.05) in jejunal mucous secretion of calves fed HSF compared with other groups. Secretions from calves fed HSF bound to many soyabean proteins in the range of 17-23 and 26-38 kDa, with similar patterns for IgA and IgG1. By contrast, only weak bands were found for IgM and IgG2 in all groups of calves. Thus, calves fed antigenic HSF do present specific Abs including IgG1 and IgA isotypes, both systemically and locally. Therefore, IgG1 and (or) IgA rather than IgM and IgG2 Abs may be preferred for assessing the immunogenicity of soyabean products in calves. Interestingly, soyabean immunogenicity was drastically reduced by adequate proteolysis.

Endomysium antibodies in coeliac disease: an improved method

The ultra structural binding sites of endomysium antibodies have been studied on human umbilical cord tissue. The sensitivity and specificity of IgA endomysium antibodies were compared with recently described methods using basement membrane of smooth muscle of monkey oesophagus. Thirty adults affected by coeliac disease (10 in remission) and 75 healthy adult controls with normal intestinal mucosa (35 false antigliadin positive) were investigated. Sensitivity and correlation of endomysium antibodies with total villous atrophy in untreated coeliac disease patients were 100% on the human umbilical cord smooth muscles, and only 90% on the muscular layer of primate oesophagus. Indirect immunofluorescence was superior to peroxidase staining in detecting these IgA antibodies. The easy availability and enhanced testing sensitivity of the umbilical cord is an advance towards a better diagnostic tool for coeliac disease.

Immune responses to dietary antigens in gluten-sensitive enteropathy of Irish setters

This study examined whether increased intestinal permeability in Irish setters with gluten-sensitive enteropathy was associated with altered immune responses to ingested antigens, and whether a humoral immune response to gluten is involved in the pathogenesis of the condition. Affected setters reared on a wheat-containing diet were compared with littermates reared on a cereal-free diet and age-matched control setters. Measurement of serum immunoglobulins revealed increased serum IgA concentrations in affected dogs. Antibody responses to a variety of dietary antigens were measured by ELISA. Antibody levels to ovalbumin, collagen I and II and soya were not significantly different from normal dogs. Anti-gliadin antibody concentrations were lower in affected dogs than controls, and correlated with immune complex formation as assessed by C1q binding. The study suggested a modified immune response in dogs with increased intestinal permeability, although there was no major systemic antibody response to dietary antigens.

Human colonic aspirates containing immunoglobulin A antibody to Clostridium difficile toxin A inhibit toxin A-receptor binding

Clostridium difficile toxin A, a 308-kilodalton protein exotoxin, is the principal causative agent of antibiotic-associated, C. difficile-induced colitis. In the current study, the prevalence of specific human serum and secretory antibody to toxin A and the possible protective effect of secretory, intestinal anti-toxin A antibody are examined. Serum (n = 35), colonic aspirates (n = 35), and duodenal aspirates (n = 20) were collected from adults at diagnostic endoscopy. Patients with evidence of colitis or a history of recent antibiotic use were excluded from the study. Specific serum immunoglobulin (Ig) A and IgG antitoxin A antibodies were detected in 60% and 57% of subjects, respectively, by enzyme-linked immunosorbent assay. Fifty-seven percent of colonic aspirates contained IgA antitoxin, whereas only 10% of duodenal aspirates were positive (P = 0.002). Binding of toxin A to its intestinal receptor was studied using [3H]toxin A and purified rabbit ileal brush border membranes. Toxin A binding was significantly inhibited by colonic aspirates with high IgA anti-toxin A antibody levels (0.503 +/- 0.055 pmol toxin A bound per milligram of brush border membrane protein, mean +/- SE) in comparison with antitoxin A-negative aspirates (0.778 +/- 0.089 pmol; P = 0.02) and control (0.766 +/- 0.004 pmol; P = 0.03). In the current study, a specific intestinal secretory IgA antibody response to C. difficile toxin A in humans is reported. This antibody response is more evident in the colon, the site of C. difficile infection, than in the upper intestinal tract. Our data suggest that human colonic IgA antitoxin may protect against C. difficile colitis by inhibiting the binding of toxin A to its intestinal epithelial cell receptor.