Macrophage chitin binding proteins in phagocytosis and M1 activation in response to chitin microparticles (172.27)

Abstract

Abstract Unlike soluble or non-phagocytosable 40 - 100 µm chitin, chitin microparticles (1 - 10 μm, CMP) induce MAPK activation within 20 min in a manner dependent on TLR2, phagocytosis and a cellular cholesterol-mediated mechanism, followed by a typical expression of M1 phenotypes. Based on the previous studies, we hypothesized that trans-membrane signal through surface TLR2 ligation is insufficient and additional chitin binding proteins (CBP) involved in the early CMP phagocytosis are obligatory for M1 activation; CBP are distinct between M1/M2 macrophages (MΦ). Peritoneal M1, M2 and control MΦ were isolated from mice 1 - 2 days after ip administration of CMP, 40 - 100 µm chitin, and saline, respectively. These MΦ were cultured with CMP; CMP with CBP were isolated shortly after phagocytosis, stained by specific antibodies and analyzed by FACS. Several CBP on CMP, including TLR2, CD206, CD62L, CHI3L1, and LAMP-1, exhibited distinct patterns between M1/M2 activations. For example, TLR2, fully engaged at the early phagocytosis, was increased in M1 and reduced in M2 relative to unstimulated MΦ. Our results suggest that, although exact mechanisms of CBP-mediated M1 activation still remain to be elucidated, the profiles of selected CBP that bind to CMP during phagocytosis are associated with the polarization of MΦ. These profiles offer a potential tool as diagnostic/prognostic biomarkers to monitor chronic inflammatory diseases and the efficacy of immunotherapy.