Effect of granulocyte-macrophage colony-stimulating factor on eicosanoid production by mononuclear phagocytes

Granulocyte-macrophage CSF (GM-CSF) primes granulocytes for leukotriene (LT) synthesis. Here, we examined the effects of GM-CSF on arachidonic acid (AA) metabolism in rat alveolar macrophages (AM), peritoneal macrophages, and human peripheral blood monocytes. Pretreatment of AMs with GM-CSF for 24 h significantly increased the synthesis of immunoreactive LTB sub(4) upon subsequent stimulation with calcium ionophore. Enhanced LT synthesis required a minimum of 6 h of GM-CSF pretreatment, suggesting that protein synthesis was required for enhanced LT production; indeed, cycloheximide completely abolished the GM-CSF effect on LT synthesis. HPLC analysis confirmed that GM-CSF primed AMs for enhanced generation of LTB sub(4) as well as the 5-lipoxygenase products LTC sub(4) and 5-HETE. Moreover, parallel increases in other AA metabolites and free AA were observed following GM-CSF pretreatment. The enhanced production of all AA metabolites indicated that GM-CSF up-regulated AA release. Consistent with this, whole cell lysates from GM-CSF-treated AMs demonstrated increased phospholipase A sub(2) (PLA sub(2)) activity. The increased activity was resistant to DTT, indicating the involvement of a PLA sub(2) other than the 14-kDa PLA sub(2)s. By immunoblot analysis, GM-CSF treatment caused an increase in the 85-kDa PLA sub(2) protein comparable to the observed increase in PLA sub(2) activity. Unlike AMs, neither peritoneal macrophages nor peripheral blood monocytes showed increased eicosanoid generation or increased expression of the 85-kDa PLA sub(2) protein following GM-CSF pretreatment. These results indicate that GM-CSF increases the capacity of AMs, but not peritoneal macrophages or peripheral blood monocytes, to generate eicosanoids. This effect results from increased PLA sub(2) activity, due at least in part to increased levels of the 85-kDa PLA sub(2) protein.