Dipeptidyl-amino-peptidase IV activity in stored buffy coat smears from human blood

The stability of dipeptidyl-amino-peptidase IV (DAP IV) activity in lymphoid cells of buffy coat smears from human blood was studied during storage for 40 days. Fixed or unfixed smears may be stored at 20 C for up to 24 hr before a decrease in activity occurs. Storage of either fixed or unfixed smears at 4 C, -10 C and -80 C results in a significant loss of activity within 24 hr. However, the cells retain more than 85% of their DAP IV activity for up to 10 days when stored fixed at -80 C. These data underscore the importance of proper processing of slides for DAP IV staining to avoid misinterpretation of results.