Monocyte chemoattractant protein-1 and secreted ectodomain of sialic acid-binding Ig-like lectin-9 enhance bone regeneration by inducing M2 macrophages

The bone-healing process consists of a primary inflammatory phase and a subsequent anti-inflammatory bone-forming phase. It was recently suggested that macrophages play an indispensable role in bone healing. Macrophages are plastic immune cells consisting of several subtypes, including pro-inflammatory M1-type and anti-inflammatory M2-type macrophages. Recently, a set of M2 macrophage inducers was described, monocyte chemoattractant protein-1 (MCP-1) and the secreted ectodomain of sialic acid-binding Ig-like lectin-9 (sSiglec-9), and applied them to a rat spinal cord injury model. Here, we hypothesized that MCP-1/sSiglec-9 enhance bone regeneration by inducing M2 macrophages.