Expression of phosphatidylserine-specific phospholipase A₁ mRNA in human THP-1-derived macrophages

The expression of phosphatidylserine-specific phospholipase A₁ (PS-PLA₁) is most upregulated in the genes of peripheral blood cells from chronic rejection model rats bearing long-term surviving cardiac allografts. The expression profile of PS-PLA₁ in peripheral blood cells responsible for the immune response may indicate a possible biological marker for rejection episodes. In this study, PS-PLA₁ mRNA expression was examined in human THP-1-derived macrophages. The effects of several immunosuppressive agents on this expression were also examined in in vitro experiments. A real-time RT-PCR analysis revealed that PS-PLA₁ mRNA expression was found in human THP-1-derived macrophages. This expression was enhanced in the cells stimulated with lipopolysaccharide (LPS), a toll-like receptor (TLR) 4 ligand. Other TLR ligands (TLR2, 3, 5, 7, and 9) did not show a significant induction of PS-PLA₁ mRNA. The time course of the mRNA expression profiles was different between PS-PLA₁ and tumor necrosis factor-α (TNF-α), which showed a maximal expression at 12 and 1 h after LPS stimulation, respectively. Among the observed immunosuppressive agents, corticosteroids, prednisolone, 6α-methylprednisolone, dexamethasone, and beclomethasone inhibited PS-PLA₁ expression with half-maximal inhibitory concentrations less than 3.0 nM, while methotrexate, cyclosporine A, tacrolimus, 6-mercaptopurine, and mycophenoic acid showed either a weak or moderate inhibition. These results suggest that the expression of PS-PLA₁ mRNA in THP-1-derived macrophages is activated via TLR4 and it is inhibited by corticosteroids, which are used at high dosages to suppress chronic allograft rejection.