Plasma CD26/DPPIV activity in SS and MF patients and healthy donors. CD26 activity measured in the plasma of SS and MF patients and compared with that of healthy donors. Using the chromogenic substrate Gly-Pro-pNA, the production of pNA by CD26 activity was monitored at 405 nm. After 30 minutes of reaction, adsorbance values (mean ± SEM from 3 separate experiments) indicated that MF and SS patients displayed, respectively, a significant reduction of CD26 activity of 26% (8.6% ± 0.43%) and 33% (7.4% ± 0.74%) when compared with controls (116% ± 1.3%). After 60 minutes the reduction was about 26% in both MF and SS. ^*Significant differences between MF/SS and controls by Student t test (MF, n = 7; SS, n = 11; P < .05).