Abstract. The cellular immune system was tested in nine patients with Whipples' disease. Three patients had active disease, and six had been in remission for up to 10 years. Intradermal delayed hypersensitivity reactions to candidin, trichophytin, tuberculin and varidase, T‐cell counts as determined by E‐rosettes, allogeneic stimulation of lymphocytes in the mixed lymphocyte culture, and mitogenic activation of lymphocytes by concanavalin A, phytohaemagglutinin and by pokeweed mitogen, were tested in the patients and compared with control subjects. HLA typing was performed in all patients. The reaction to tuberculin and varidase, the T‐cell counts and the activation of lymphocytes by concanavalin A were significantly reduced in patients with active disease and in patients during remission. The reaction to candidin and trichophytin was poor even in the controls. The mean results of the mixed lymphocyte culture, phytohaemagglutinin, and pokeweed mitogen activation tests were not significantly different from the controls. In patients with active disease the mixed lymphocyte culture reaction and the T‐cell counts were less than in patients in remission. The results suggest a persistent defect of T‐cells in patients with Whipple's disease, a defect that is more severe in patients with active disease. The finding of HLA B27 in four of the nine patients supports the hypothesis of primary rather than secondary impairment of the cellular immune system in Whipple's disease. Copyright © 1979, Wiley Blackwell. All rights reserved
