Abstract: Objective  To explore the  immune mechanism of βendorphin(βEP) in  ulcerative colitis(UC) patients.Methods  Thirty  UC  patients were enrolled， including  mild activity 8 cases， moderate activty 10 cases  and  severe activity 12 cases.  In the same period，15 patients with colon polyps served as control group.  Blood  βEP and interleukin1β(IL1β)   were measured by radioimmunoassay. After peripheral blood lymphocyte separation， CD3+ T cells， CD4+ T cells and CD4+/CD8+ T cells percentage were detected by flow cytometry.  βEP  and  IL1β in colon mucosa were measured by immunohistochemistry.  Results  Plasma expressions of βEP， IL1β， CD4+ T cells， CD4+/CD8+ T cells percentage in patients with UC were significantly higher than those of control group (P<0.05).  And the expressions  showed significant difference with the disease severity: patients with mild UC<patients with moderate UC<patients with severe UC (P<0.05). Colonic expressions of βEP， IL1β in patients with UC were significantly higher than those in control group (P<0.05).  Plasma βEP between the active phase and the remission phase was positively correlated with the change of IL1β，CD4+ T cells，CD4+/CD8+ T cells percentage(r=0.522，P<0.01；r=0.532，P<0.05；r=0.964，P<0.01). Conclusion   βEP may play a role in the immunological mechanism of UC by regulating the leukomonocyte subgroup and the secretion of IL1β，in a certain way，βEP reflects the severity of UC patients.

Key words: colitis, ulcerative, betaendorphin, interleukin1beta, Tlymphocyte , subsets, immunomodulation