Cell–Cell Interaction of Macrophages and Vascular Smooth Muscle Cells in the Synthesis of Leukotriene B4

Biosynthesis of LTB(4) during cell-cell interaction between vascular smooth muscle cells (SMC) and alveolar macrophages (AM) has been investigated by use of both high-pressure Hquid chromatography (HPLC) and radtoimmunoassay (RIA). Both interleukin-beta (IL-beta) and tumour necrosis factor-alpha (TNFalpha) induced a time- and dose-dependent synthesis of 15-, and 5-hydroxyeicosatetraenoic acids (HETEs) from cultured SMC. However, neither TNFalpha nor IL-1beta induced a significant LTB(4) production in SMC alone or AM alone after 24 h of incubation. Addition of IL-1beta and TNFalpha simultaneously to SMC resulted in a dose-dependent synergistic increase of HETEs. Macrophages dose-dependently transformed extremely low concentrations of exogenous LTA(4) into LTB(4). Incubation of vascular SMC with various numbers of AM in the presence of IL-1beta (5 units/ml) and TNFalpha (10 units/ml) induced a great increase of LTB(4) synthesis in comparison with the detectable levels of LTB(4) produced by macrophages alone. Pretreatment of SMC with NDGA, cycloheximide, and actinomycin not only inhibited IL-1 and TNT induced HETEs synthesis but also abolished LTB(4) production when co-incubated with macrophages. These results suggest that LTB(4) in a mixture of SMC and macrophages could originate from a transcellular metabolism, i.e. macrophages transforming SMC-derived LTA(4) into LTB(4).