TLR4 and chronic obstructive pulmonary disease: Although bacterial LPSs generally act as activators of TLR4 and play a role in downstream inflammatory activation, in an interesting study, the LPS derived from an intestinal commensal bacterium, Parabacteroides goldsteinii, was found to be the main component that ameliorated a cigarette-smoke-induced COPD murine model by acting as an antagonist for TLR4 and consequently reducing the over-expression of proinflammatory cytokines such as IL-1β and TNF-α in the lungs and colon in COPD mice [92].