Haemoglobin triggers chemotaxis of human monocyte-derived dendritic cells: possible role in atherosclerotic lesion instability

OBJECTIVE: Mechanisms that drive innate immune cell recruitment into atherosclerotic lesions are still not well defined. We tested the role of haemoglobin (Hb) to promote chemotaxis, adhesion to endothelial cells and transendothelial migration of human monocytes and monocyte-derived immature dendritic cells (iDCs) and its possible role in atherogenic cell recruitment. METHODS AND RESULTS: We demonstrated that Hb triggers chemotaxis, adhesion to endothelial cells and transendothelial migration of monocytes and monocyte-derived iDCs. Innate immune cell chemotaxis significantly increased in the presence of Hb in a dose-dependent manner involving extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) activation and actin remodeling. The pre-treatment of cells with pre-titrated concentration of the anti-CD163 blocking antibody reduced the Hb-induced cell migration, thus suggesting the involvement of CD163 receptor. Conversely, N-acetyl cysteine and soluble Hb-scavenger protein haptoglobin (Hp) inhibited the Hb-induced iDC migration. Finally, spontaneous iDC migration significantly increased in the presence of serum of patients with haemorrhagic complicated plaques and partially decreased in the presence of Hp. CONCLUSION: Hb by interacting with CD163 on monocytes and iDCs might induce cell recruitment and activation within vascular wall, thus contributing to the complex cross talk of chemotactic signals that mediate atherosclerotic lesions instability.