Relationship between phosphatidylserine exposure and serum-dependent opsonization in phagocytes

Abstract

AIM: To investigate the relationship between the exposure of phosphatidylserine(PS) and serum-dependent opsonization in peripheral blood mononuclear cells(PBMCs), to lay a foundation for exploring the influence of physiological microenvironment on the function of phagocytes.MET HODS: PBMCs were isolated from the peripheral blood of healthy individuals using Ficoll-paque and treated by RPMI 1640 medium with or without serum after washing with PBS. The phosphatidylserine(PS) exposure was detected by annexin V staining before and after in vitro serum incubation. Malondialdehyde(MDA) in treated PBMCs was examined by spect rophotometry to evaluate the interference of lipid peroxidation. The PS exposure in different subsets of PBMCs was analyzed by flow cytometry with antiCD3, anti-CD56 and anti-HLA-DR staining. Phagocytosis was detected by FCM after incubation with bacteria expressing green fluorescent protein(GFP). RESULTS: PS+ cells significantly increased in PBMCs after serum incubation, and shortterm serum incubation immediately induced the increase of PS+ cells. Serum incubation had no influence on the membrane MDAcontent, which excluded the interference by the products of lipid peroxidation. Cell subset analysis showed that HLA-DR+ mononuclear phagocytes were the main cells exposing PS in PBMCs and significantly increased in Annexin V+ cells. Bacterial phagocytosis showed that the exposed PS was involved in the serumdependent opsonization. CONCLUSION: The exposure of PS is serumdependent and is involved in the opsonization of bacteria by PBMCs.