Role of Ca2+ in prostaglandin E2-induced T-lymphocyte proliferative suppression in sepsis

Abstract

Prostaglandin E2 (PGE2) has been known to modulate immune responses by inhibiting T-cell activation following hemorrhagic and traumatic injury. Recently, we documented a sepsis-related depression in concanavalin A (ConA)- induced T-cell proliferation and intracellular Ca2+ (Ca2+(i)) mobilization. The present study evaluated the potential role of PGE2 in the sepsis-related attenuation in Ca2+ signaling and proliferation in T cells. Sepsis was induced in rats by implanting into their abdomen fecal pellets containing Escherichia coli (150 CFU) and Bacteroides fragilis (104 CFU). A group of rats implanted with septic pellets were treated with indomethacin at three consecutive time points. Levels of PGE2 in blood were measured with a radioimmunoassay kit. ConA-induced [Ca2+](i) mobilization in T cells obtained from indomethacin-treated and untreated rats was measured with Fura- 2 and microfluorometry. We observed a 10-fold increase in PGE2 levels in the circulation of septic rots compared with levels in rats implanted with bacterium-free sterilized pellets. The proliferative response and Ca2+(i) mobilization were significantly depressed in T cells obtained from septic rats 48 h after implantations compared with those in rats implanted with sterile pellets. However, treatment of rats with the cyclooxygenase inhibitor indomethacin prevented the sepsis-related depression in ConA-induced T-cell Ca2+, mobilization as well as proliferation. Further, incubation of T cells from nonimplanted control rats with PGE2 resulted in a substantial depression in both T-cell proliferation and Ca2+(i) mobilization. The restoration of T-cell proliferation and Ca2+ signaling after indomethacin treatment of septic rats and the depression in the mitogen responsiveness in T cells previously exposed to PGE2 suggest that the PGE2 does play a significant role in the modulation of T-cell responses in septic rats and that such PGE2-induced suppression in T-cell activation is likely due to an attenuation in Ca2+ signaling.