Chlamydia pneumoniae binds to platelets and triggers P-selectin expression and aggregation: a causal role in cardiovascular disease?
OBJECTIVE
Evidence linking Chlamydia pneumoniae to atherosclerotic cardiovascular disease is expanding. Platelets are considered to play an essential role in cardiovascular diseases; however, so far platelets have not been associated with an infectious cause of atherosclerosis. This study aims to clarify the interaction between C pneumoniae and platelets and possibly present a novel mechanism in the pathogenesis of atherosclerosis.


RESULTS
The effects of C pneumoniae on platelet aggregation and secretion were assessed with lumiaggregometry, and the ability of C pneumoniae to bind to platelets and stimulate expression of P-selectin was analyzed with flow cytometry. We found that C pneumoniae, at a chlamydia:platelet ratio of 1:15, adheres to platelets and triggers P-selectin expression after 1 minute and causes an extensive aggregation and ATP secretion after 20 minutes of incubation. Inhibition of glycoprotein IIb/IIIa with Arg-Gly-Asp-Ser or abciximab markedly reduced C pneumoniae-induced platelet aggregation. Exposure of C pneumoniae to polymyxin B, but not elevated temperature, abolished the stimulatory effects on platelet activation, suggesting that chlamydial lipopolysaccharide has an active role. In contrast, other tested bacteria had no or only moderate effects on platelet functions.


CONCLUSIONS
Our findings demonstrate a new concept of how C pneumoniae activates platelets and thereby may cause atherosclerosis and thrombotic vascular occlusion.
Kälvegren
Hanna
H
Division of Medical Microbiology, Department of Molecular and Clinical Medicine, Faculty of Health Sciences, Linköping University, Sweden. hanjo@imk.liu.se
Majeed
Meytham
M
Bengtsson
Torbjörn
T
D001422:Bacterial Adhesion; D001792:Blood Platelets / Q000737:chemistry / Q000378:metabolism* / Q000382:microbiology*; D002318:Cardiovascular Diseases / Q000382:microbiology*; D002460:Cell Line; D002690:Chlamydia Infections / Q000382:microbiology*; D016993:Chlamydophila pneumoniae / Q000472:pathogenicity / Q000502:physiology*; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism; D019007:P-Selectin / Q000096:biosynthesis*; D015539:Platelet Activation / Q000502:physiology; D010974:Platelet Aggregation / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000502:physiology; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000502:physiology; D012486:Salmonella typhimurium / Q000378:metabolism; D013211:Staphylococcus aureus / Q000378:metabolism; D013212:Staphylococcus epidermidis / Q000378:metabolism
D008070:Lipopolysaccharides; D019007:P-Selectin; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex