Analysis of anti-gliadin antibodies by immunoblot analysis and enzyme-linked immunosorbent assay using gliadin fractions as antigens

Generation and selection of anti-flagellin monoclonal antibodies useful for serotyping Salmonella enterica

In developing countries, bacterial acute gastroenteritis continues to be an important cause of morbidity and mortality among young children. Salmonellosis constitutes a major cause of infectious enteritis worldwide, most of them associated to the consumption of contaminated food products. Traditionally, Salmonella has been classified in serovars based on varieties of O and H surface antigens. In the present work we generated and characterized a panel of anti-flagellin monoclonal antibodies (MAbs) in order to select antibodies useful for detecting the H surface antigen. Four different MAbs were obtained by somatic hybridization of splenocytes. We found two MAbs that recognised regions of flagellin conserved among different Salmonella serovars. Other two MAbs recognised structures restricted to Salmonella enterica sv. Typhimurium, being one of them suitable for agglutination tests. Using a diverse panel of S. enterica serovars with different H antigen varieties we confirmed that this MAb agglutinates specifically S. Typhimurium (antigenic formula: 4,12:i:1,2) or other serovars expressing flagellar factor i. In conclusion, we generated a valuable immunochemical tool to be used in simple assays for serotyping of epidemiologically relevant strains. The capacity to characterize specific strains and determine the primary sources of Salmonella contamination generate valuable information of the epidemiology of this microorganism, contributing to the improvement of public health.

Different profiles of wheat antigens are recognised by patients suffering from coeliac disease and IgE-mediated food allergy

BACKGROUND

Dietary intake of wheat can cause two distinct immunologically mediated diseases with severe gastrointestinal manifestations, coeliac disease (CD) and IgE-mediated food allergy. The pathomechanisms underlying these diseases are different, but the profile of the target antigens in wheat has not been compared for the two diseases.

METHODS

We compared IgA- and IgE-reactive antigens in wheat using sera from patients with coeliac disease (n = 35) and food allergy to wheat (n = 16) by one- and two-dimensional immunoblotting. Furthermore, the IgG subclass (IgG1-IgG4) reactivity to wheat antigens was studied by enzyme-linked immunosorbent assay.

RESULTS

IgA antibodies from CD patients and IgE antibodies from allergic patients recognised distinct profiles of wheat antigens. Furthermore, the IgG subclass responses to wheat antigens were different in CD and wheat-allergic patients.

CONCLUSION

This study thus demonstrates that wheat contains antigens/epitopes which are preferentially recognised by CD patients, whereas others elicit IgE-mediated food allergy. This finding suggests that the nature of a food antigen may influence the quality of the pathological immune response in the gut and has implications for the diagnosis and therapy of hypersensitivity to wheat.

The diagnostic accuracy of serologic tests for celiac disease: a systematic review

Clinicians are increasingly utilizing noninvasive serologic tests for the diagnosis and screening of celiac disease (CD). The aim of this study was to conduct a systematic review of the diagnostic performance of serologic tests for the diagnosis and screening of CD. Standard systematic review methodology was used. A literature search was conducted in MEDLINE (1966 to October 2003) and EMBASE (1974 to December 2003) databases. A weighted mean of the sensitivity and specificity along with 95% confidence intervals and summary receiver operating characteristic (ROC) curves were calculated. The pooled specificity of endomyseal antibody (EMA)-monkey esophagus (ME) or EMA-human umbilical cord (HU) was close to 100% in adults and children. The pooled specificity of transglutaminase antibody (tTG)-guinea pig (GP) and tTG-human recombinant (HR) were between 95% and 99%. IgA-EMA-ME demonstrated sensitivities of 96% and 97% in children and adults, respectively. EMA-HU demonstrated a similar sensitivity of 97% in children but 90% in adults. The pooled sensitivity of tTG-GP in adults and children was 90% and 93%, respectively. The sensitivity of tTG-HR was 98% and 96%, respectively. The performance of antigliadin antibody was inferior to that of EMA and tTG. EMA and tTG offer high sensitivity and specificity. The sensitivity of these tests appears to be lower than reported when milder histologic grades are used to define CD (below 90%). If true, the nearly perfect negative predictive value of these tests would drop. The positive predictive value of these tests is likely lower than reported when the tests are applied in low-prevalence populations.

Evaluation of coeliac disease serological markers in Down syndrome patients

BACKGROUND

The increased incidence of coeliac disease in patients with Down syndrome makes screening of coeliac disease in this population advisable.

AIM

Evaluation of efficiency of different serological markers to detect coeliac disease in Down syndrome patients.

PATIENTS

A total of 56 Down syndrome patients (aged: 1-17 years) were included in study.

METHODS

Patients were evaluated for both IgG and IgA anti-transglutaminase antibodies and for anti-gliadin IgA and IgG antibodies using either purified omega-gliadin, wheat ethanol extract or commercial gliadin. Patients who had at least one positive result were evaluated for antiendomysium antibodies using either monkey oesophagus or human umbilical cord by indirect immunofluorescence. Coeliac disease was diagnosed by typical histological changes on duodenal mucosa.

RESULTS

Increased levels of at least one anti-gliadin IgA and IgG antibody marker were found in 27 out of 56 cases (26 for IgG and 9 for IgA). 11/56 were positive for IgG anti-transglutaminase antibodies and two of them were also positive for IgA anti-transglutaminase antibodies and anti-endomysium antibodies. These two patients were finally diagnosed as coeliacs. Gliadin antigenic fractions employed produced differences in the performance of the anti-gliadin IgA and IgG antibody test. The use of commercial gliadin or wheat ethanol extract showed low sensitivity in IgA anti-gliadin IgA and IgG antibody determination, whereas good sensitivity and specificity were observed with omega-gliadins. IgG anti-transglutaminase antibodies showed a high proportion of false positive results (9 out of 56), whereas anti-endomysium antibodies and IgA anti-transglutaminase antibodies presented an excellent correlation with presence of active coeliac disease.

CONCLUSIONS

Two out of 56 Down syndrome patients were diagnosed as coeliacs, corresponding to an incidence of 3.6%. The use of omega-gliadin presented the best efficiency in anti-gliadin IgA and IgG antibody determination whereas IgA anti-transglutaminase antibodies and anti-endomysium antibody determination showed an absolute correlation with presence of active coeliac disease.

Determination of anti-omega-gliadin antibodies in serologic tests for coeliac disease

BACKGROUND

Serologic detection of coeliac disease in the general population or in subjects belonging to risk groups implies the use of a test with high efficiency, large-scale use, and low cost. The enzyme-linked immunosorbent assay (ELISA) technique is the most appropriate assay for performing this kind of studies. Even though anti-gliadin determination has been the test most frequently used as the first step in screening procedures, many false-positive results produced a low-specificity test. In a previous work a selective recognition of omega-gliadins, mainly by IgA antibodies, was observed. Results also indicated that omega-gliadins can be useful as antigens in serologic detection of coeliac disease. We therefore wanted to analyse the anti-gliadin antibody reactivity by using purified gliadins and to evaluate the actual performance of the anti-omega-gliadin antibody test.

METHODS

A population consisting of 105 coeliac patients, 81 healthy controls, and 73 subjects in a disease control group was analysed. Anti-endomysium (EMA), both IgG and IgA anti-omega-gliadins, and anti-tissue transglutaminase (tTG) antibodies were determined.

RESULTS

Concordant results, positive and negative, in the EMA and IgG and IgA anti-gliadin determinations were observed in 220 of 259 samples from the total population analysed. The three assays showed high efficiency, being 96.9%, 90.7%, and 91.1% for EMA and anti-omega-gliadins IgG and IgA, respectively. Anti-tTG determination was performed on 103 samples (69 controls and 34 coeliac patients), finding 4 false results (2 false positive and 2 false negative), whereas anti-omega-gliadins showed 10 false results (5 false negative and 5 false positive), 3 of which were coincident with anti-tTG determination. To compare the reactivity of anti-gliadin antibodies, alpha-, beta-, gamma- and omega-gliadins were isolated under non-denaturing conditions by acid preparative electrophoresis and cation-exchange fast protein liquid chromatography (FPLC) and used in an indirect ELISA test. The composition of these fractions was analysed by means of capillary electrophoresis, showing no cross-contamination among them.

CONCLUSIONS

The comparison of results using purified gliadins shows that omega-gliadins present a differential reactivity that has not previously been documented. Results using omega-gliadins isolated by either preparative electrophoresis or FPLC were similar. Tests using the purified omega-gliadin fraction present the best performance when anti-gliadin antibodies are evaluated.