Dipeptidyl peptidase IV (DP IV, CD26) in patients with inflammatory bowel disease

Background: Dipeptidyl peptidase IV (DP IV. CD26), a serine protease with broad tissue distribution and known activity in serum, participates in T cell activation and promotes a Th1 cytokine response, a function in part attributable to its enzymatic activity, We hypothesized that the activity of DP IV in serum and expression of CD26/DP IV in lymphocytes may be altered in patients with inflammatory bowel disease (IBD), Methods: Serum DP IV activity and CD26 (DP IV)-positive peripheral blood lymphocytes were measured in 110 patients with IBD) (Crohn disease (CD): n = 63, ulcerative colitis (UC): n = 47). Additionally, T cell activation antigens (CD25 CD95) and costimulatory molecules (CD28) were evaluated. The same analyses were carried out in healthy volunteers (HC, n = 28). Thirty-nine patients with CD and 28 patients with UC were reassessed 3-6 months after the first visit. Results: In patients with IBD, the DP IV activity in serum was reduced (mean +/- s (standard deviation): 52.8 U/I +/- 16.9 (CD) and 55.7 +/- 15.1 U/I (UC) versus 71.9 +/- 18.4 (HC), P < 0.001). Furthermore, patients with IBD had higher numbers of CD26-positive cells coexpressing CD25 and a higher surface expression of CD26 (DP IV) (mean fluorescence intensity, mean 57.1 (CD) and 59.8 (UC) versus 29.9 (HC), P < 0.001). The DP IV activity in serum showed an inverse correlation with known disease activity scores as well as with the concentrations of orosomucoid in serum. Conclusion: The changes of DP IV in patients with IBD highlight alterations at an interface between immune function and metabolism of peptide hormones, with potential importance for the pathophysiology of IBD, Furthermore, these changes may help to refine the assessment of IBD activity.