The effect of azathioprine on cell-mediated immunity (CMI) to Candida albicans in Crohn's disease.

Using as antigen a suspension of , strain A, three tests of cell-mediated immune reactivity (delayed skin hypersensitivity, lymphocyte stimulation and leucocyte migration inhibition) were undertaken in patients with Crohn's disease to determine the effect of azathioprine given as the sole anti-inflammatory medication. No significant effect was demonstrable on 48 hr induration in the skin test. Uptake of thymidine by lymphocytes , whether spontaneous or antigenically induced, was greater during azathioprine treatment than before it. The assumption that this finding might be associated with clinical recovery was confirmed in antigen-stimulated cultures by the fact that, irrespective of treatment, patients who had been able to resume their normal occupations showed markedly higher reactivity than those who were still disabled (<0·002). It was also found that azathioprine treatment in itself potentiated lymphocyte stimulation by . The range of values for inhibition of leucocyte migration was the same in the treated and untreated groups, but certain individuals displayed a substantial change in reactivity when re-tested after institution or discontinuation of azathioprine treatment. Untreated patients with Crohn's disease did not differ from normal subjects in their cell-mediated reactivity to . The increased rate of thymidine uptake by lymphocytes from patients receiving azathioprine is discussed in the light of recent hypotheses linking virus-induced malignancy with lymphoblastic transformation.