Affinity maturation of immunoglobulin A anti-tissue transglutaminase autoantibodies during development of coeliac disease

Anti-Lipid IgG Antibodies Are Produced via Germinal Centers in a Murine Model Resembling Human Lupus

Anti-lipid IgG antibodies are produced in some mycobacterial infections and in certain autoimmune diseases [such as anti-phospholipid syndrome, systemic lupus erythematosus (SLE)]. However, few studies have addressed the B cell responses underlying the production of these immunoglobulins. Anti-lipid IgG antibodies are consistently found in a murine model resembling human lupus induced by chlorpromazine-stabilized non-bilayer phospholipid arrangements (NPA). NPA are transitory lipid associations found in the membranes of most cells; when NPA are stabilized they can become immunogenic and induce specific IgG antibodies, which appear to be involved in the development of the mouse model of lupus. Of note, anti-NPA antibodies are also detected in patients with SLE and leprosy. We used this model of lupus to investigate in vivo the cellular mechanisms that lead to the production of anti-lipid, class-switched IgG antibodies. In this murine lupus model, we found plasma cells (Gr1⁻, CD19⁻, CD138⁺) producing NPA-specific IgGs in the draining lymph nodes, the spleen, and the bone marrow. We also found a significant number of germinal center B cells (IgD⁻, CD19⁺, PNA⁺) specific for NPA in the draining lymph nodes and the spleen, and we identified in situ the presence of NPA in these germinal centers. By contrast, very few NPA-specific, extrafollicular reaction B cells (B220⁺, Blimp1⁺) were found. Moreover, when assessing the anti-NPA IgG antibodies produced during the experimental protocol, we found that the affinity of these antibodies progressively increased over time. Altogether, our data indicate that, in this murine model resembling human lupus, B cells produce anti-NPA IgG antibodies mainly via germinal centers.

Serum autoantibodies directed against transglutaminase-2 have a low avidity compared with alloantibodies against gliadin in coeliac disease

Coeliac disease is characterized by intolerance to gliadin and related gluten components present in wheat, barley and rye. Coeliac disease patients harbour antibodies directed against alloantigens such as gliadin, but also against the autoantigen transglutaminase-2 (TG2). The type and quality of antibody responses provides insight into the underlying immune activation processes. Therefore, in this study we have analysed the avidity of the antibody response directed against the autoantigen TG2 and compared this with antibody responses against the alloantigens gliadin and Escherichia coli. We observed that the immunoglobulin (Ig)A autoantibody response directed against TG2 is of low avidity compared with the IgA response against the alloantigens gliadin and E. coli in the same patients; the same was true for IgG, both in IgA-deficient and in -sufficient coeliac patients. The observed avidities appear not to be related to disease stage, antibody levels, age or duration of exposure to gluten. In conclusion, in coeliac disease there is a clear difference in avidity of the antibody responses directed against the auto- and alloantigens, indicating different regulation or site of initiation of these responses.

A biopsy is not always necessary to diagnose celiac disease

OBJECTIVES

Small intestinal histology is the criterion standard for the diagnosis of celiac disease (CD). However, results of serological tests such as anti-endomysium antibodies and anti-tissue transglutaminase antibodies (tTGA) are becoming increasingly reliable. This raises the question of whether a small intestinal biopsy is always necessary. The aim of the present study was, therefore, to investigate whether a small intestinal biopsy can be avoided in a selected group of patients.

PATIENTS AND METHODS

Serology and histological slides obtained from 283 pediatric patients suspected of having CD were examined retrospectively. The response to a gluten-free diet (GFD) in patients with a tTGA level ≥ 100 U/mL was investigated.

RESULTS

A tTGA level ≥ 100 U/mL was found in 128 of the 283 patients. Upon microscopic examination of the small intestinal epithelium, villous atrophy was found in 124 of these patients, confirming the presence of CD. Three patients had crypt hyperplasia or an increased number of intraepithelial lymphocytes. In 1 patient no histological abnormalities were found. This patient did not respond to a GFD.

CONCLUSIONS

Pediatric patients with a tTGA level ≥ 100 U/mL in whom symptoms improve upon consuming a GFD may not need a small intestinal biopsy to confirm CD.

Intestinal transglutaminase 2 specific antibody deposits in non-responsive coeliac disease

BACKGROUND AND AIMS

The diagnosis of coeliac disease is problematic in individuals not responding to a gluten-free diet. Small-bowel villous atrophy occurs in other enteropathies and non-responsive patients are often seronegative. We investigated whether small-bowel mucosal transglutaminase-2 specific autoantibody deposits distinguish non-responsive coeliac disease from other enteropathies.

METHODS

Small-bowel mucosal autoantibody deposits were determined in 27 non-responsive, 28 responsive coeliac patients and 10 controls with other enteropathies. Of the non-responsive coeliac patients six were adhering poorly and 21 strictly to the diet; six of the 21 had enteropathy-associated lymphoma, five refractory coeliac disease and 10 otherwise persistent villous atrophy. The presence of mucosal autoantibody deposits was compared to serology, villous morphology, densities of intraepithelial lymphocytes (IELs) and markers of refractory coeliac disease.

RESULTS

Twenty out of 21 well-adhering, all six poorly adhering non-responsive and all 28 untreated responsive coeliac patients had small-bowel mucosal autoantibody deposits present, while controls with other enteropathies were negative. Small-bowel mucosal autoantibody deposits were more accurate in detecting coeliac disease than serology or IEL densities. Refractory coeliac markers revealed only cases with the most severe condition.

CONCLUSIONS

Small-bowel mucosal autoantibody deposits differentiate coeliac disease from other enteropathies, enabling the design of appropriate therapeutic strategies.

Anti-transglutaminase antibodies in non-coeliac children suffering from infectious diseases

Anti-transglutaminase antibodies are the diagnostic markers of coeliac disease. A role is suggested for infectious agents in the production of anti-transglutaminase antibodies. The aim was to measure positive anti-transglutaminase antibody levels in children with infectious diseases and to compare immunological and biological characteristics of the anti-transglutaminase antibodies derived from these children with that from coeliac patients. Two hundred and twenty-two children suffering from infectious diseases were enrolled prospectively along with seven biopsy-proven coeliacs. Serum samples were tested for anti-transglutaminase antibodies and anti-endomysium antibodies; positive samples were tested for coeliac-related human leucocyte antigen (HLA)-DQ2/8 and anti-viral antibodies. Purified anti-transglutaminase antibodies from the two study groups were tested for urea-dependent avidity, and their ability to induce cytoskeletal rearrangement and to modulate cell-cycle in Caco-2 cells, using phalloidin staining and bromodeoxyuridine incorporation assays, respectively. Nine of 222 children (4%) tested positive to anti-transglutaminase, one of whom also tested positive for anti-endomysium antibodies. This patient was positive for HLA-DQ2 and was diagnosed as coeliac following intestinal biopsy. Of the eight remaining children, two were positive for HLA-DQ8. Levels of anti-transglutaminase returned to normal in all subjects, despite a gluten-containing diet. Purified anti-transglutaminase of the two study groups induced actin rearrangements and cell-cycle progression. During an infectious disease, anti-transglutaminase antibodies can be produced temporarily and independently of gluten. The infection-triggered anti-transglutaminase antibodies have the same biological properties as that of the coeliacs, with the same in-vivo potential for damage.