TLR4 and pulmonary fibrosis: Lipopolysaccharides (LPS), membrane components of gram-negative bacteria, recognized by the membrane receptor TLR4, have been involved in experimental lung fibrosis (109, 110), are capable of promoting fibroblast proliferation in vitro (111) and induce the early secretion of IL-1β, MCP-1/CCL2 or IL-8 by AEC2 (112, 113).