K. Kett

Mucosal subclass distribution of immunoglobulin G-producing cells is different in ulcerative colitis and Crohn's disease of the colon

As a marked local immunoglobulin G (IgG) response has previously been found to be the most prominent immunopathological feature of both ulcerative colitis and Crohns disease, the subclass distribution of colonic IgG-producing immunocytes was examined. This study included tissue specimens from 10 patients with ulcerative colitis and 8 with Crohns colitis. Paired immunofluorescence staining was performed with subclass-specific murine monoclonal antibodies combined with a rabbit antibody reagent of IgG; the proportion of cells belonging to each subclass could thereby be determined in relation to the total number of mucosal IgG immunocytes. A significantly higher median proportion of IgG1 immunocytes was found in ulcerative colitis (81.3%) than in Crohns colitis (66.5%). Conversely, the median proportion of IgG2 immunocytes was significantly higher in Crohns colitis (24.9%) than in ulcerative colitis (9.4%). This disparity in the local IgG subclass response might reflect dissimilar mucosal exposure to mitogenetic or antigenic stimuli or genetically determined immunoregulatory differences in the two categories of patients.

Gliadin specific, HLA DQ2-restricted T cells are commonly found in small intestinal biopsies from coeliac disease patients, but not from controls.

The authors have analysed gliadin specific, CD4+ T cells isolated from small intestinal biopsies of 23 adult coeliac disease patients (20 on a gluten‐free diet and three untreated) and nine control patients. The biopsies were stimulated ex vivo with a peptic/tryptic digest of gliadin for 24 h, and activated T cells were positively selected with paramagnetic beads coated with an antibody against the interleukin‐2 receptor. The T cells were expanded and tested for gliadin reactivity and HLA restriction. Gliadin specific, polyclonal T cell lines were recovered from biopsies of all 23 patients. Inhibition studies of T cell lines from 21 patients with anti‐HLA monoclonal antibodies indicated predominant presentation of the gliadin antigen by HLA‐DQ2 in T cell lines from 11 patients (lines from seven patients with complete MoAb inhibition, the remaining with incomplete inhibition) and incomplete inhibition by HLA‐DR3 in lines from three patients. Nine gliadin specific T cell clones from six patients were established; all of these were HLA‐DQ2 restricted. Gliadin specific T cells were not found in biopsies from the non‐coeliac controls. Our findings demonstrate that gliadin reactive T cells are commonly found in the intestinal mucosa of CD patients and they support the notion that the majority of T cells recognize gliadin peptide(s) when presented by the disease associated DQ2 molecules.

Intestinal B-cell isotype response in relation to local bacterial load: Evidence for immunoglobulin A subclass adaptation☆

BACKGROUND & AIMS In experimental animals, the indigenous microbiota modulates mucosal immunity. In humans, such direct evidence is scarce. The aim of this study was to examine the effect of intestinal bacteria on the local immunoglobulin (Ig) response. METHODS The numbers of IgA-, IgM-, and IgG-producing immunocytes per defined mucosal length unit were determined, and the local IgA subclass response was studied using immunohistochemistry in jejunal segments from adults with bacterial overgrowth and in sterile ileal urinary conduits from children. RESULTS The ileal bladder mucosa showed atrophy, but the number of immunocytes only tended to be decreased. The jejunal segments with bacterial overgrowth showed minor histological changes; the numbers of IgA and IgG immunocytes were fairly normal, whereas the number of IgM immunocytes was significantly reduced (P < 0.05) (12 cells/U) compared with control mucosa (24 cells/U). The number of IgA2 immunocytes was significantly decreased (P < 0.01) in ileal conduits (7 cells/U or 30% of total IgA) but increased (P < 0.05) in jejunal segments with bacterial overgrowth (42 cells/U or 43% of total IgA) compared with normal ileum (15 cells/U or 40% of total IgA) and jejunum (24 cells/U or 23% of total IgA). CONCLUSIONS An association exists between bacterial load and IgA subclass production. An increase in IgA2 may enhance mucosal protection and probably reflects immunomodulation caused by lipopolysaccharides.

J-chain expression is more prominent in immunoglobulin A2 than in immunoglobulin A1 colonic immunocytes and is decreased in both subclasses associated with inflammatory bowel disease

Paired immunofluorescence staining demonstrated reduced J-chain positivity of both immunoglobulin A1 (IgA1)- and IgA2-producing cells in colonic mucosa from patients with ulcerative colitis and Crohns colitis compared with controls (p less than 0.002). J-chain expression was generally higher in IgA2 than in IgA1 immunocytes. The median proportion in normal mucosa was 100% for IgA2 vs. 88% for IgA1 (p less than 0.005); in ulcerative colitis, 69% vs. 46% (p less than 0.004); and in Crohns colitis, 74% vs. 46% (p less than 0.004). Taken together with the overall IgA-subclass distribution, however, these results showed that the proportion of J-chain-positive IgA2 cells in the total IgA-cell population was lower for ulcerative colitis (20%) and Crohns colitis (32%) than for normal mucosa (63%) (p less than 0.002). In relation to the total J-chain-positive IgA-cell population, which contributes to the secretory IgA system, an increased proportion (p less than 0.002) belonged to IgA1 in ulcerative colitis (61% vs. normal, 27%), whereas IgA2 was reduced (39% vs. normal, 73%). Similar but smaller trends were noted in Crohns colitis. The disease-associated reduction of J chain might be compensated by the previously reported twofold numeric increase of IgA cells in colitis. Our study, therefore, did not suggest that the secretory IgA-cell system was quantitatively impaired in inflammatory bowel disease.

Gliadin-Specific T Cell Responses in Peripheral Blood of Healthy Individuals Involve T Cells Restricted by the Coeliac Disease Associated DQ2 Heterodimer

Coeliac disease (CD) is probably caused by an abnormal immune response towards wheat gliadin in the small intestine. We found that gliadin‐specific T cells from the small intestinal mucosa of HLA‐DQ2 positive CD patients were almost exclusively restricted by the disease‐associated DQ2 molecule. In the peripheral blood of CD patients, a large proportion of gliadin‐specific T cells were found to be restricted by DQ molecules, including DQ2, but many were instead restricted by DR or DP molecules of the patient. We have now investigated gliadin‐specific T cell responses in peripheral blood from healthy individuals. Four of 20 persons tested had strong in vitro responses and were used as donors for gliadin‐specific T cell clones. We found gliadin‐specific T cells restricted by the CD‐associated DQ2 molecule in peripheral blood for two of these four individuals. It is the presence of such T cells also in the small intestinal mucosa which seems typical of CD.

Secretory immunity in celiac disease: Cellular expression of immunoglobulin a subclass and joining chain

Two-color immunofluorescence staining in situ demonstrated increased proportions of immunoglobulin A2 subclass-producing cells in jejunal mucosa from adult patients with untreated (47%, P less than 0.01) or treated (37%, P less than 0.05) celiac disease compared with controls (28%). Costaining was also performed for joining chain, which is a key factor in the epithelial transport of secretory antibodies; its expression by immunoglobulin A2 cells was only marginally reduced in untreated patients (96%) compared with treated patients and controls (98%). Also, immunoglobulin A1 cells showed similar joining chain positivity (89%) in all three groups. Considering the expanded total jejunal immunoglobulin A-cell population and the subclass-associated joining chain expression, it could be calculated that the potential of immunoglobulin A2 cells for contribution to secretory immunity was increased 3.9 times in untreated (P less than 0.01) and 1.8 times in treated (P less than 0.05) patients and that of immunoglobulin A1 cells was increased 1.7 times in untreated (P less than 0.05) but remained unaltered in treated patients. The estimated relative contributions of locally produced immunoglobulin A2 to secretory immunoglobulin A would thus be 51% and 37% in the two patient categories, respectively, compared with 31% in the controls. These data suggested enhanced secretory immunity in celiac disease and might reflect a protective, possibly antimicrobial, immune response. It could not be excluded, however, that increased generation of secretory immunoglobulin A at the same time contributes to the gluten-induced pathogenesis of celiac disease.