Chlamydia pneumoniae burden in carotid arteries is associated with upregulation of plaque interleukin-6 and elevated C-reactive protein in serum.
OBJECTIVE
Chlamydia pneumoniae (Cpn) infection of vascular smooth muscle cells increases interleukin-6 (IL-6) secretion in vitro. In vivo, IL-6 stimulates liver C-reactive protein (CRP) production. Because serum levels of IL-6 and CRP are independent risk factors for stroke and myocardial infarction (MI), we investigated whether Cpn burden in carotid plaques might provide a link between plaque IL-6 expression and elevated serum levels of IL-6 and CRP.


RESULTS
Consecutive patients undergoing elective carotid endarterectomy were studied. Serum levels of CRP and IL-6 were measured before surgery. Immunohistochemistry and real-time quantitative (k)RT-PCR were used to detect Cpn and the expression of IL-6 within carotid plaques. Cpn mRNA was present in 19 (37%) of 51 patients, suggesting viable infections. These patients had evidence for infection by PCR and immunohistochemistry. The Cpn burden, measured by real-time quantitative (k)-PCR using the number of organisms normalized against the number of eukaryotic cells in the tissue, was associated with plaque expression of IL-6 (Spearman R=0.55; P<0.0001), which was associated with serum levels of IL-6 (R=0.56; P<0.0001) and CRP (R=0.80; P<0.0001).


CONCLUSIONS
IL-6 secretion in atherosclerotic plaques infected with Cpn could explain elevated serum inflammatory markers in individuals at risk for stroke and MI.
Johnston
S Claiborne
SC
Department of Neurology, University of California, San Francisco, CA, USA.
Zhang
Hui
H
Messina
Louis M
LM
Lawton
Michael T
MT
Dean
Deborah
D
D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000378:metabolism*; D002339:Carotid Arteries / Q000276:immunology / Q000382:microbiology; D002340:Carotid Artery Diseases / Q000453:epidemiology / Q000276:immunology* / Q000382:microbiology*; D023521:Chlamydophila Infections / Q000150:complications / Q000453:epidemiology / Q000276:immunology*; D016993:Chlamydophila pneumoniae / Q000302:isolation & purification*; D016894:Endarterectomy, Carotid; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D015850:Interleukin-6 / Q000097:blood* / Q000235:genetics; D008297:Male; D008875:Middle Aged; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012307:Risk Factors; D015854:Up-Regulation / Q000276:immunology; D014657:Vasculitis / Q000453:epidemiology / Q000276:immunology / Q000382:microbiology
D015415:Biomarkers; D015850:Interleukin-6; D002097:C-Reactive Protein