Immunoregulatory function of lamina propria T cells in Crohn's disease

The pathogenesis of Crohn's disease may involve altered function of immunoregulatory T cells in the intestine. To investigate this hypothesis, lamina propria lymphocytes were isolated from intestinal specimens resected from patients with active Crohn's disease and control subjects (colon carcinoma and diverticular disease) using an enzymatic technique. The T-cell phenotypes and function of these lymphocytes were compared with that of peripheral blood lymphocytes. The proportion of Leu-2-positive (suppressor/cytotoxic) cells was similar in peripheral blood and isolated lamina propria lymphocytes, both in Crohn's disease and control patients. Although the proportion of Leu-3-positive (helper/inducer) lymphocytes was lower in lamina propria lymphocytes than peripheral blood lymphocytes, there was no difference comparing Crohn's disease and control patients. Helper T-cell function, as determined by measuring the ability of T cells to increase immunoglobulin synthesis by pokeweed mitogen-stimulated normal peripheral blood B cells, was similar in peripheral blood lymphocytes and lamina propria lymphocytes, and comparing Crohn's disease with control patients. Suppressor T-cell function, as determined by measuring the ability of T cells to inhibit immunoglobulin production by cultures containing pokeweed mitogen-stimulated normal peripheral blood T and B cells, was also similar comparing peripheral blood lymphocytes and lamina propria lymphocytes, and comparing Crohn's disease with control patients: neither peripheral blood lymphocytes nor lamina propria lymphocytes significantly suppressed immunoglobulin synthesis. OKT8 (suppressor/cytotoxic)-enriched lamina propria lymphocytes mediated only marginal suppression, whereas concanavalin A-activated intestinal T cells did mediate significant suppression, in both Crohn's disease and control patients. Thus, patients with active Crohn's disease have no alteration of immunoregulatory T-cell function for polyclonal mitogen-induced immunoglobulin synthesis at the gut mucosal level, despite the presence of an inflammatory process in the intestine.