Synthetic Prostacyclin Analogs Differentially Regulate Macrophage Function via Distinct Analog-Receptor Binding Specificities

PGI2 (prostacyclin) is a lipid mediator with vasodilatory and antithrombotic effects used in the treatment of vasoconstrictive/ischemic diseases including pulmonary artery hypertension. However, emerging research supports a role for PGs, including PGI2, in the regulation of both innate and acquired immunity. As PGI2 is unstable, we sought to define the effects of various PGI2 analogs on resident alveolar macrophage (AM) and peritoneal macrophage (PM) innate immune functions. The effects of iloprost, carbaprostacyclin, and treprostinil on the regulation of phagocytosis, bacterial killing, and inflammatory mediator production were determined in both macrophage populations from rats. Iloprost failed to suppress AM functions to the same degree that it did in PMs, a characteristic shared by carbaprostacyclin. This difference reflected greater expression of the Gαs protein-coupled I prostanoid receptor and greater cAMP generation in PMs than AMs. Treprostinil inhibited phagocytosis, bacterial killing, and cytokine generation in AMs to a much greater degree than the other PGI2 analogs and more closely resembled the effects of PGE2. Studies with the E prostanoid (EP) 2 receptor antagonist AH-6809 and EP2-null macrophages indicated that this was due in part to the previously unknown ability of treprostinil to stimulate the EP2 receptor. The present investigation for the first time identifies differences in immunoregulatory properties of clinically administered PGI2 analogs. These studies are the first to explore the capacity of PGI2 to regulate bacterial killing and phagocytosis in macrophages, and our findings may hold important consequences regarding the risk of infection for patients receiving such agents.