Immunohistochemical characterization of local immunoglobulin formation in Crohn's disease of the ileum.

Paired direct immunofluorescence was used to localize and differentially enumerate immunocytes containing the various immunoglobulin (Ig) classes in ileal bowel walls of patients with Crohn's disease. In slightly inflamed mucosa the total number of Ig-containing cells of an average "tissue unit" increased threefold compared with normal controls, but only minor changes occurred in class ratios. In severely inflamed mucosa with persisting glands, the total immunocyte number was increased by a factor of 12.2 compared with the control unit. For IgA, IgM, and IgG cells this increase was 9.0, 12.0, and 60.9, respectively. The immunocyte ratios for these three major Ig classes were 57.5:14.7:27.7 in the inflamed mucosa, and 83.1:11.4:5.4 in the histologically normal control mucosa. When severely inflamed specimens from the ileum and from the colon were compared, there was no statistically significant difference in absolute immunocyte counts or class distributions. IgD and IgE immunocytes were extremely rare, and no consistent increase was found in the inflamed mucosae. In both the ileum and the colon fairly dense immunocyte populations with a marked IgG-cell predominance were encountered in the deeper layers of the inflamed bowel wall. The possible pathogenetic consequences of the pronounced local "over-production" of IgG in inflammatory bowel disease are discussed.