TLR4 and chronic obstructive pulmonary disease: Chlamydial viability and virulence were confirmed by detecting the expression of chlamydial heat shock protein 60 messenger ribonucleic acid in an acute Chlamydia infection model.[23] C-X-C motif chemokine ligand (CXCL)-8 expression, an important early innate response mediator, and Toll-like receptor 2 (TLR2), but not Toll-like receptor 4 (TLR4), were significantly increased in the acute Chlamydia infection model compared to COPD patients with persistent Chlamydia infection.