Glu496 to Ala polymorphism in the P2X7 receptor impairs ATP-induced IL-1β release from human monocytes

Priming of monocytes with LPS produces large quantities of intracellular, biologically inactive 11,40 that can be processed and released by subsequent activation of the P2X(7) receptor by extracellular ATP. We examined whether a loss-of-function polymorphism of the human P2X(7) receptor (Glu(496) Ala) impairs this process. Both ATP-induced ethidium(+) uptake and ATP-induced shedding of L-selectin (CD62L) were nearly absent in monocytes; from four subjects homozygous for Glu(496) Ala confirming that this polymorphism impairs P2X(7) function. The level of ATP-induced IL-1beta released in 2 h from LPS-activated whole blood from homozygous subjects was 50% of that from wild-type samples. A more marked defect in IL-1beta release was observed from LPS-activated monocytes of homozygous subjects which was only 22% of that released from wild-type monocytes after a 30-min incubation with ATE However, after a 60-min incubation with ATP, the amount of IL-1beta released from homozygous monocytes was 70% of that released from wild-type monocytes. Incubation of monocytes of either genotype with nigericin resulted in a similar release of IL-1beta. Western blotting demonstrated that ATP induced the release of mature 17-kDa IL-1beta from monocytes, and confirmed that this process was impaired in homozygous; monocytes. Finally, ATP-induced Rb-86(+) efflux was 9-fold lower from homozygous monocytes than from wild-type monocytes. The results indicate that ATP-induced release of IL-1beta is slower in monocytes from subjects homozygous for the Glu(496)Ala polymorphism in the P2X(7) receptor and that this reduced rate of IL-1beta release is associated with a lower ATP-induced K+ efflux.