Elevated serum dipeptidyl peptidase IV activity in patients with chronic tonsillitis

Palatine tonsils represent the first place of contact for a variety of antigenic substances present in air and food. Upon antigen stimulation, the interactions between T and B lymphocytes in the tonsil are known to depend on the expression of different co-stimulatory molecules, including proteolytic ectoenzymes. Dipeptidyl peptidase IV (DPP IV) and aminopeptidase N (APN), as T lymphocyte co-stimulatory molecules, participate in the regulation of the immune response during inflammation.

In this study, the serum and lymphocyte enzymatic activity of DPP IV and APN was investigated in 32 patients, 13 with recurrent tonsillitis (RT) and 19 with tonsillar hypertrophy (TH), before and one month after tonsillectomy. The enzymatic activity of DPP IV and APN in tonsillar lymphocytes and serum was determined kinetically at 37 degrees C using Gly-Pro-p-nitroanilide (for DPP IV) and Ala-p-nitroanilide (for APN) as chromogenic substrates.

Significantly higher serum DPP IV and APN activities (P<0.001) were found in TH patients compared with those with RT before tonsillectomy. DPP IV activity in TH patients was also elevated compared with the control of the same age (P<0.001), whereas the activity of APN was the same as the control group. The activity of both enzymes was the same as of controls after tonsillectomy. In addition, the results show that DPP IV and APN activities in serum decrease significantly with age. Tonsillar lymphocytes demonstrated a wide range of DPP IV and APN activities without significant differences between the investigated groups.

An increased serum DPP IV activity was observed in TH patients compared with both RT patients and controls before tonsillectomy. After tonsillectomy, all activities were similar. The results suggest that serum DPP IV activity may have potential as a diagnostic marker for patients with TH.