Immunosuppression in the treatment of inflammatory bowel disease. I. Changes in lymphoid sub-populations in the blood and rectal mucosa following cessation of treatment with azathioprine

Lymphoid subpopulations in the blood and rectal mucosa were studied in six patients with ulcerative colitis or Crohn's disease who had been treated for over three years with azathioprine. Serial assays were performed to observe the changes occurring up to 12 weeks after treatment with azathioprine was stopped. While the patients were on the drug two lymphoid populations showed marked depression. These were the plasma cells of the rectal lamina propria, and blood lymphocytes with cytotoxic activity against antibody-sensitized target cells (`K' cells). After stopping azathioprine, both populations showed a rapid rise to reach near normal levels by 12 weeks. Most of the recovery occurred within 3–5 weeks. There was no significant change in circulating immunoglobulin-staining cells which could be attributed to the drug. Nor was azathioprine shown to have any effect on the mitotic response of lymphocytes to phytohaemagglutinin. Three patients, however, gave very low or erratic responses to PHA, which may have been related either to their disease or to steroid therapy. These results are discussed in relation to the mode of action of purine analogues as immunosuppressive agents.