LDL and IL-6 induce TGF-β1 release and mast cell migration toward intimal macrophages.

Objective and design: This study tests the hypothesis that mast cells migration to the artery's intimal layer occurs due to release of TGF-β1 from macrophages exposed to LDL and IL-6. Material or subjects: Human monocytic cells (THP-1), human mast cells (LUVA), and human umbilical vein endothelial cells (HUVEC). Treatment: THP-1 cells were differentiated into M0, M1, and M2 macrophages, which were then treated with LDL, oxidized LDL (oxLDL), IL-6, or a combination of LDL and IL-6. LUVA cells and HUVEC were exposed to conditioned media from untreated and treated macrophages. LUVA cells were also exposed to TGF-β1. Methods: The concentration of TNF-α and TGF-β1 released from macrophages was measured by ELISA. The migration of LUVA cells in a microfluidic channel was assessed for 12 h. THP-1 cell adhesion to HUVEC was investigated under static conditions. Results: Inflammatory (M1) macrophages exposed to LDL + IL-6 or oxLDL released TGF-β1 at the level close to anti-inflammatory (M2) macrophages. These M2-like cells kept their inflammatory properties, based on adhesion data. The LUVA cells migrated to TGF-β1 or the conditioned medium from M2-like macrophages. Conclusions: LDL in combination with IL-6 repolarized macrophages from M1 to M2-like cells, which attracted mast cells via TGF-β1.