Heat shock protein 60 from Chlamydia pneumoniae elicits an unusual set of inflammatory responses via Toll‐like receptor 2 and 4 in vivo

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Abstract
Heat shock protein 60 (HSP60) from Chlamydia pneumoniae was described to trigger in vitro inflammatory and cytokine responses including TNF and IL‐12p40. Although it can be found in atherosclerotic plaques of patients, the stimulatory potential of chlamydial and other HSP60 in vivo is unclear. We now report that chlamydial HSP60 fails to induce TNF expression in vivo, and significant serum levels of IL‐12p40 are only found upon intraperitoneal injection of high doses of HSP60 or after intravenous application. Upon purification of chlamydial HSP60 with polymyxin B‐agarose columns, its ability to induce TNF secretion in vitro is much reduced. However, purified chlamydial HSP60 causes increased serum levels of the CXC chemokines KC and MIP2 in vivo, as well as a strong accumulation of polymorphonuclear neutrophils (PMN) in the peritoneal cavity upon intraperitoneal challenge. With respect to PMN accumulation, chlamydial HSP60 is more potent than endotoxin or the CpG oligonucleotide 1668. The responses observed are completely abolished in Toll‐like receptor (TLR)2/4‐double‐deficient mice, while single‐deficient mice respond almost normally. Furthermore, KC induction and PMN accumulation are largely dependent on MyD88. In conclusion, HSP60 from C. pneumoniae triggers inflammatory responses in vivo that differ from responses induced by endotoxin or CpG oligonucleotides and are dependent on TLR2 and 4.