PARP1 and cystic fibrosis: We measured PARP-1 activity in CF and non-CF primary HBEs by using ELISA to determine the rate at which its substrate NAD+ is assembled into polymers of ADP-Ribose as illustrated in Figure 1A. PARP-1 activity was 2.9-fold higher in HBEs from two CF patients when compared with cells from two non-CF subjects (Figure 1B, Students t-test, P < 0.05).