TLR2 and lung cancer: Lung cancer cell-derived exosomes can activate Toll-like receptor 2 (TLR2)/NF-κB signaling via their surface heat shock protein 70, converting naïve MSCs in PMN into a new pro-inflammatory MSC that secretes IL-6, IL-8 and human monocyte chemotactic protein-1(MCP-1) to maintain a low-grade inflammatory microenvironment (20).