Phagocytosis-mediated M1 activation by chitin but not by chitosan

• Published in: American Journal of Physiology: Cell Physiology 2018-07, Vol.315 (1), p.C62-C72
• Main Authors: Davis, Spring, Cirone, Aiko M, Menzie, Janet, Russell, Floyd, Dorey, C Kathleen, Shibata, Yoshimi, Wei, Jianning, Nan, Changlong
• Format: Article
• Language: English
• Subjects: Actin; Adaptor proteins; Allergens; CD14 antigen; Cell activation; Cell growth; Chitin; Chitinase; Chitosan; Genes; Interleukin 1; Interleukin 1 receptors; Lck protein; Lyn protein; Macrophages; MAP kinase; Microparticles; MyD88 protein; Pathogens; Phagocytosis; Protein-tyrosine kinase; Proteins; Rapamycin; Tissues; TLR1 protein; TLR2 protein; Toll-like receptors; TOR protein
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00268.2017

Chitin particles have been used to understand host response to chitin-containing pathogens and allergens and are known to induce a wide range of polarized macrophage activations, depending, at least in part, on particle size. Nonphagocytosable particles larger than a macrophage induce tissue repair M2 activation. In contrast, phagocytosable chitin microparticles (CMPs, 1-10 μm diameters) induce M1 macrophages that kill intracellular microbes and damage tissues. However, chitosan (deacetylated) microparticles (de-CMPs, 1-10 µm) induce poor M1 activation. Toll-like receptor 2 (TLR2) and associated coreceptors in macrophages appear to be required for the M1 activation. To understand the exact mechanism of phagocytosis-mediated M1 activation by chitin, we isolated macrophage proteins that bind to CMPs during early phagocytosis and determined that TLR1, TLR2, CD14, late endosomal/lysosomal adaptor MAPK and mechanistic target of rapamycin activator 1 (LAMTOR1), Lck/Yes novel tyrosine kinase (Lyn), and β-actin formed phagosomal CMP-TLR2 clusters. These proteins were also detected in TLR2 phagosomal clusters in macrophages phagocytosing de-CMPs, but at relatively lower levels than in the CMP-TLR2 clusters. Importantly, CMP-TLR2 clusters further recruited myeloid differentiation primary response gene 88 (MyD88) and Toll-IL-1 receptor-containing adaptor protein (TIRAP) and phosphorylated Lyn, whereas neither the adaptors nor phosphorylated Lyn was detected in the de-CMP clusters. The results indicate that the acetyl group played an obligatory, phagocytosis-dependent role in the initiation of an integrated signal for TLR2-mediated M1 activation.