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

Abstract

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 Crohn's 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 Crohn's 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 Crohn's 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 Crohn's 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.