Evidence for predominant involvement of the B-cell system in the inflammatory process in Crohn's disease.

The cellular infiltrate in the walls of resected ileum and colon specimens obtained from patients with Crohn's disease was analysed. Mononuclear cells in tissue sections were characterized by the use of surface membrane markers and immuno-histochemical and enzyme histochemical techniques. It was found that: [1] B cells, as judged by the presence of surface membrane immunoglobulin and C3 receptors and the absence of alpha-naphthylacetate esterase and acid phosphatase activity, were the predominant type of cells in the intestinal infiltrate often found in close relation with smaller numbers of non-B cells; [2] all types of immunoglobulin-containing cells were increased in number with a shift in the ratio of IgA/IgG/IgM-containing cells in favour of the IgG- and IgM-containing cells; and [3] the histopathological reaction of the regional draining lymph nodes showed hyperplasia of B-cell areas (follicles and medulla) and small or absent T-cell areas (paracortex), consistent with a B-cell response. Our results indicate that the inflammatory process in the bowel wall in Crohn's disease mainly reflects stimulation of the B-cell system.