Melinda Ráki

HLA-DQ2 and -DQ8 signatures of gluten T cell epitopes in celiac disease

Celiac disease is associated with HLA-DQ2 and, to a lesser extent, HLA-DQ8. Type 1 diabetes is associated with the same DQ molecules in the opposite order and with possible involvement of trans-encoded DQ heterodimers. T cells that are reactive with gluten peptides deamidated by transglutaminase 2 and invariably restricted by DQ2 or DQ8 can be isolated from celiac lesions. We used intestinal T cells from celiac patients to map DQ2 and DQ8 epitopes within 2 representative gluten proteins, alpha-gliadin AJ133612 and gamma-gliadin M36999. For alpha-gliadin, DQ2- and DQ8-restricted T cells recognized deamidated peptides of 2 separate regions. For gamma-gliadin, DQ2- and DQ8-restricted T cells recognized deamidated peptides of the same region. Some gamma-gliadin peptides were recognized by T cells in the context of DQ2 or DQ8 when bound in exactly the same registers, but with different requirements for deamidation; deamidation at peptide position 4 (P4) was important for DQ2-restricted T cells, whereas deamidation at P1 and/or P9 was important for DQ8-restricted T cells. Peptides combining the DQ2 and DQ8 signatures could be presented by DQ2, DQ8, and trans-encoded DQ heterodimers. Our findings shed light on the basis for the HLA associations in celiac disease and type 1 diabetes.

Tetramer visualization of gut-homing gluten-specific T cells in the peripheral blood of celiac disease patients

Tetramers of MHC–peptide complexes are used for detection and characterization of antigen-specific T cell responses, but they require knowledge about both antigenic peptide and the MHC restriction element. The successful application of these reagents in human diseases involving CD4+ T cells is limited. Celiac disease, an intestinal inflammation driven by mucosal CD4+ T cells recognizing wheat gluten peptides in the context of disease-associated HLA-DQ molecules, is an ideal model to test the potential clinical use of these reagents. We investigated whether gluten-specific T cells can be detected in the peripheral blood of celiac disease patients using DQ2 tetramers. Nine DQ2+ patients and six control individuals on a gluten-free diet were recruited to the study. Participants consumed 160 g of gluten-containing bread daily for 3 days. After bread-challenge, gluten-specific T cells were detectable in the peripheral blood of celiac patients but not controls both directly by tetramer staining and indirectly by enzyme-linked immunospot. These T cells expressed the β7 integrin indicative of gut-homing properties. Most of the cells had a memory phenotype, but many other phenotypic markers showed a heterogeneous pattern. Tetramer staining of gluten-specific T cells has the potential to be used for diagnosis of celiac disease.

HLA-DQ2-restricted gluten-reactive T cells produce IL-21 but not IL-17 or IL-22

We have analyzed the production of the effector cytokines interleukin (IL)-17, IL-21, and IL-22 in gluten-reactive CD4+ T cells of celiac disease patients, either cultured from small intestinal biopsies or isolated from peripheral blood after an oral gluten challenge. Combining intracellular cytokine staining with DQ2-α-II gliadin peptide tetramer staining of intestinal polyclonal T-cell lines, we found that gluten-specific T cells produced interferon-γ (IFN-γ) and IL-21, but not IL-17 or IL-22, even if other T cells of the same lines produced these cytokines. Similarly, in DQ2-α-II-specific T cells in peripheral blood of gluten-challenged patients, very few stained for intracellular IL-17, whereas many cells stained for IFN-γ. We conclude that gluten-reactive T cells produce IL-21 and IFN-γ, but not IL-17. Their production of IL-21 suggests a role for this cytokine in the pathogenesis of celiac disease.

Posttranslational Modification of Gluten Shapes TCR Usage in Celiac Disease

Posttranslational modification of Ag is implicated in several autoimmune diseases. In celiac disease, a cereal gluten-induced enteropathy with several autoimmune features, T cell recognition of the gluten Ag is heavily dependent on the posttranslational conversion of Gln to Glu residues. Evidence suggests that the enhanced recognition of deamidated gluten peptides results from improved peptide binding to the MHC and TCR interaction with the peptide–MHC complex. In this study, we report that there is a biased usage of TCR Vβ6.7 chain among TCRs reactive to the immunodominant DQ2-α-II gliadin epitope. We isolated Vβ6.7 and DQ2-αII tetramer-positive CD4+ T cells from peripheral blood of gluten-challenged celiac patients and sequenced the TCRs of a large number of single T cells. TCR sequence analysis revealed in vivo clonal expansion, convergent recombination, semipublic response, and the notable conservation of a non-germline-encoded Arg residue in the CDR3β loop. Functional testing of a prototype DQ2-α-II–reactive TCR by analysis of TCR transfectants and soluble single-chain TCRs indicate that the deamidated residue in the DQ2-α-II peptide poses constraints on the TCR structure in which the conserved Arg residue is a critical element. The findings have implications for understanding T cell responses to posttranslationally modified Ags.

Rapid Generation of Rotavirus-Specific Human Monoclonal Antibodies from Small-Intestinal Mucosa

The gut mucosal surface is efficiently protected by Abs, and this site represents one of the richest compartments of Ab-secreting cells in the body. A simple and effective method to generate Ag-specific human monoclonal Abs (hmAbs) from such cells is lacking. In this paper, we describe a method to generate hmAbs from single Ag-specific IgA- or IgM-secreting cells of the intestinal mucosa. We found that CD138-positive plasma cells from the duodenum expressed surface IgA or IgM. Using eGFP-labeled virus-like particles, we harnessed the surface Ig expression to detect rotavirus-specific plasma cells at low frequency (0.03–0.35%) in 9 of 10 adult subjects. Single cells were isolated by FACS, and as they were viable, further testing of secreted Abs by ELISPOT and ELISA indicated a highly specific selection procedure. Ab genes from single cells of three donors were cloned, sequenced, and expressed as recombinant hmAbs. Of 26 cloned H chain Ab genes, 22 were IgA and 4 were IgM. The genes were highly mutated, and there was an overrepresentation of the VH4 family. Of 10 expressed hmAbs, 8 were rotavirus-reactive (6 with Kd < 1 × 10−10). Importantly, our method allows generation of hmAbs from cells implicated in the protection of mucosal surfaces, and it can potentially be used in passive vaccination efforts and for discovery of epitopes directly relevant to human immunity.

Assessing possible celiac disease by an HLA-DQ2-gliadin Tetramer Test.

OBJECTIVES:Investigation of uncertain celiac disease (CD) in patients already on a gluten-free diet (GFD) is difficult. We evaluated HLA-DQ2-gliadin tetramers for detection of gluten-specific T cells in peripheral blood and histological changes in the duodenum after a short gluten challenge as a diagnostic tool.METHODS:HLA-DQ2+ individuals on a GFD for at least 4 weeks were investigated; 35 with uncertain diagnosis, 13 CD patients, and 2 disease controls. All participants had a challenge with four slices of gluten-containing white bread, daily for 3 days (d1–d3). An esophagogastroduodenoscopy with biopsy sampling was done on d0 and d4. Biopsies were scored according to revised Marsh criteria. Peripheral blood CD4+ T cells were isolated, stained with HLA-DQ2-gliadin peptide tetramers, and analyzed by flow cytometry on d0 and d6.RESULTS:After challenge, a positive tetramer test was seen in 11/13 CD patients. Four of these subjects also showed typical histological changes on challenge. Of the 35 patients with uncertain diagnosis, 3 were diagnosed with CD. Two of these three patients had both positive tetramer staining and histological changes in biopsies after challenge.CONCLUSIONS:Tetramer staining for gluten-specific T cells is a sensitive method in detecting an immune response in CD patients after a short gluten challenge. The prevalence of CD in the group with self-prescribed GFD was about 10%.

The adaptive immune response in celiac disease

Compared to other human leukocyte antigen (HLA)-associated diseases such as type 1 diabetes, multiple sclerosis, and rheumatoid arthritis, fundamental aspects of the pathogenesis in celiac disease are relatively well understood. This is mostly because the causative antigen in celiac disease—cereal gluten proteins—is known and the culprit HLA molecules are well defined. This has facilitated the dissection of the disease-relevant CD4+ T cells interacting with the disease-associated HLA molecules. In addition, celiac disease has distinct antibody responses to gluten and the autoantigen transglutaminase 2, which give strong handles to understand all sides of the adaptive immune response leading to disease. Here we review recent developments in the understanding of the role of T cells, B cells, and antigen-presenting cells in the pathogenic immune response of this instructive disorder.

Rapid Accumulation of CD14+CD11c+ Dendritic Cells in Gut Mucosa of Celiac Disease after in vivo Gluten Challenge

Background Of antigen-presenting cells (APCs) expressing HLA-DQ molecules in the celiac disease (CD) lesion, CD11c+ dendritic cells (DCs) co-expressing the monocyte marker CD14 are increased, whereas other DC subsets (CD1c+ or CD103+) and CD163+CD11c− macrophages are all decreased. It is unclear whether these changes result from chronic inflammation or whether they represent early events in the gluten response. We have addressed this in a model of in vivo gluten challenge. Methods Treated HLA-DQ2+ CD patients (n = 12) and HLA-DQ2+ gluten-sensitive control subjects (n = 12) on a gluten-free diet (GFD) were orally challenged with gluten for three days. Duodenal biopsies obtained before and after gluten challenge were subjected to immunohistochemistry. Single cell digests of duodenal biopsies from healthy controls (n = 4), treated CD (n = 3) and untreated CD (n = 3) patients were analyzed by flow cytometry. Results In treated CD patients, the gluten challenge increased the density of CD14+CD11c+ DCs, whereas the density of CD103+CD11c+ DCs and CD163+CD11c− macrophages decreased, and the density of CD1c+CD11c+ DCs remained unchanged. Most CD14+CD11c+ DCs co-expressed CCR2. The density of neutrophils also increased in the challenged mucosa, but in most patients no architectural changes or increase of CD3+ intraepithelial lymphocytes (IELs) were found. In control tissue no significant changes were observed. Conclusions Rapid accumulation of CD14+CD11c+ DCs is specific to CD and precedes changes in mucosal architecture, indicating that this DC subset may be directly involved in the immunopathology of the disease. The expression of CCR2 and CD14 on the accumulating CD11c+ DCs indicates that these cells are newly recruited monocytes.

Tetramer-visualized gluten-specific CD4+ T cells in blood as a potential diagnostic marker for coeliac disease without oral gluten challenge

Background Diagnosing coeliac disease (CD) can be challenging, despite highly specific autoantibodies and typical mucosal changes in the small intestine. The T-cell response to gluten is a hallmark of the disease that has been hitherto unexploited in clinical work-up. Objectives We aimed to develop a new method that directly visualizes and characterizes gluten-reactive CD4+ T cells in blood, independently of gluten challenge, and to explore its diagnostic potential. Methods We performed bead-enrichment of DQ2.5-glia-α1a and DQ2.5-glia-α2 tetramer+ cells in the blood of control individuals, treated (TCD) and untreated patients (UCD). We visualized these cells by flow cytometry, sorted them and cloned them. We assessed their specificity by antigen stimulation and re-staining with tetramers. Results We detected significantly more gliadin-tetramer+ CD4+ effector memory T cells (TEM) in UCD and TCD patients, compared to controls. Significantly more gliadin-tetramer+ TEM in the CD patients than in controls expressed the gut-homing marker integrin-β7. Conclusion Quantification of gut-homing, gluten-specific TEM in peripheral blood, visualized with human leukocyte antigen (HLA) -tetramers, may be used to distinguish CD patients from healthy individuals. Easy access to gluten-reactive blood T cells from diseased and healthy individuals may lead to new insights on the disease-driving CD4+ T cells in CD.

Density of CD163+CD11c+ Dendritic Cells Increases and CD103+ Dendritic Cells Decreases in the Coeliac Lesion

Coeliac disease is a chronic inflammation of the intestinal mucosa controlled by gluten‐specific T cells restricted by disease‐associated HLA‐DQ molecules. We have previously reported that mucosal CD11c+ dendritic cells (DCs) are responsible for activation of gluten‐reactive T cells within the coeliac lesion. In mice, intestinal CD11c+ DCs comprise several functionally distinct subsets. Here, we report that HLA‐DQ+ antigen‐presenting cells (APCs) in normal human duodenal mucosa can be divided into four subsets with striking similarities to those described in mice: CD163+CD11c− macrophages (74%), and CD11c+ cells expressing either CD163 (7%), CD103 (11%) or CD1c (13%). CD103+ and CD1c+ DCs belonged to partly overlapping populations, whereas CD163+CD11c+ APCs appeared to be a distinct population. In the coeliac lesion, we found increased density of CD163+CD11c+ APCs, whereas the density of CD103+ and CD1c+ DCs was decreased, suggesting that distinct subpopulations of APCs in coeliac disease may exert different functions in the pathogenesis.