Preliminary studies from our laboratory showed that cPLA2α may be responsible for approximately 50-60% of the PGE2 production in response to inflammatory cytokines. Thus, we hypothesized that a closely-related PLA2 is responsible for 40-50% of the PGE2 produced in response to inflammatory cytokines. To this end, we utilized RNAi technology, extensively optimized, to down regulate the expression of closely-related isoforms of phospholipase A2 in A549 cells and used an enzyme linked immuno sorbent assay (ELISA) to quantitate the PGE2 produced. These studies found that cytosolic phospholipase A2α (cPLA2α) regulated 97.7% of the prostaglandin E2 (PGE2) produced in response to inflammatory cytokines (e.g. IL-1β or TNFα), as well as regulating the basal levels of this prostanoid. Furthermore, cPLA2γ, cPLA2δ, and iPLA2 were found to also to regulate the basal levels of PGE2 production. On the other hand, cPLA2β was not involved in prostanoid synthesis in A549 cells either in the presence or absence of inflammatory cytokines. Thus, our studies show that cPLA2α plays the pivotal role in the production of PGE2 in response to inflammatory cytokines, and suggests that cPLA2α may be a possible drug target in diseases such as asthma, inflammation, and cancer.