Interaction between intestinal and peripheral blood mononuclear cells.

Effective methods are available to isolated immunocytes from human intestinal mucosa. Isolated mononuclear cells from the mucosa of patients with Crohn's disease and normal controls were classified according to ultrastructure and cell-surface profile by the use of a panel of monoclonal antibodies. In both compartments of the mucosa, i.e., the lamina propria and the epithelial layer, no differences were found between intestinal tissue from control patients and unaffected mucosa of patients with Crohn's disease. Inflamed mucosa was characterized by an accumulation of surface-Ig+ cells and, to a lesser degree, of monocytes and granulocytes. The predominant T cell phenotypes were a T4 cell in the lamina propria and a T8 cell in the epithelial layer. Most of the isolated immunocytes were found to be HLA/DR. Analysis of the functional properties of mucosa-associated T cells in a pokeweed-stimulated autologous B cell assay revealed that T cells originating from normal mucosa enhance the generation of IgA-producing B cells, whereas those from chronically inflamed mucosa do not. In contrast, peripheral T cells from patients with Crohn's disease favour expression of the IgA isotype, as compared with peripheral T cells from normal controls. Removal of Fc + T4 cells resulted in a significantly reduced number of IgA B cells. These findings point to an alteration of isotypic immunoregulation in Crohn's disease. It is postulated that a shift from IgA to IgG and IgM in the local immune response could result in antibody-dependent cytotoxicity for enterocytes.