CHLAMYDIAL HEAT-SHOCK-PROTEIN-60 LOCALIZES IN HUMAN ATHEROMA AND REGULATES MACROPHAGE TUMOR-NECROSIS-FACTOR-ALPHA AND MATRIX METALLOPROTEINASE EXPRESSION

Background-Recent evidence has implicated Chlamydia pneumoniae in the aggravation of atherosclerosis. However, the mechanisms by which this agent affects atherogenesis remain poorly understood. Chlamydiae produ ce large amounts of heat shock protein 60 (HSP 60) during chronic, per sistent infections, and C pneumoniae localizes predominantly within pl aque macrophages, Several studies have furnished evidence that endogen ous (human) HSP 60 may play a role in atherogenesis. We tested here th e hypothesis that atheroma contains chlamydial HSP 60 and that this ba cterial product might stimulate macrophage functions considered releva nt to atherosclerosis and its complications, such as production of pro inflammatory cytokines as tissue necrosis factor-cu (TNF-alpha) and ma trix-degrading metalloproteinases (MMPs). Methods and Results-Surgical specimens of human carotid atherosclerotic arteries (n=19) and normal arterial wall samples (n=7, 2 carotid arteries and 5 aortas) were tes ted immunohistochemically for the presence of chlamydial HSP 60 and hu man HSP 60. Macrophage localization of these antigens was assessed by double immunostaining. Murine peritoneal macrophages, maintained in se rum-free conditions for 48 hours after harvesting, were incubated with C pneumoniae, chlamydial HSP 60, human HSP 60, or Escherichia coli li popolysaccharide (LPS). Culture supernatants, collected at 24 hours fo r concentration-dependence experiments and at up to 72 hours for time- dependence experiments, were analyzed for TNF-alpha by ELISA and for M MP by gelatin zymography. Atherosclerotic lesions showed immunoreactiv e chlamydial HSP 60 in 47% (9 of 19) of the cases and human HSP 60 in 89% (17 of 19) of the cases. Chlamydial HSP 60 colocalized with human HSP 60 within plaque macrophages in 77% (7 of 9) of the cases. Nonathe rosclerotic samples contained neither HSP. Both C pneumoniae and recom binant chlamydial HSP 60 induced TNF-alpha production by mouse macroph ages in a concentration- and time-dependent fashion. E coli LPS and hu man HSP 60 produced similar effects. Similarly, C pneumoniae and HSPs induced MMPs in a concentration- and time-dependent manner. Heat treat ment abolished the effect of C pneumoniae and HSPs on both TNF-alpha a nd MMP production, but it did not alter the ability of E coli LPS to i nduce these functions. Conclusions-Chlamydial HSP 60 frequently coloca lizes with human HSP 60 in plaque macrophages in human atherosclerotic lesions. Chlamydial and human HSP 60 induce TNF-alpha and MMP product ion by macrophages. Chlamydial HSP 60 might mediate the induction of t hese effects by C pneumoniae. Induction of such macrophage functions p rovides potential mechanisms by which chlamydial infections may promot e atherogenesis and precipitate acute ischemic events.