Efficient phagocytosis of periodontopathogens by neutrophils requires plasma factors, platelets and TLR2.
BACKGROUND
Periodontitis represents a chronic infection of supportive dental tissues by distinct gram-negative bacteria. It is characterized by chronic and local inflammation as well as transient bacteremia with frequently occurring infections at distant sites.


OBJECTIVE
The present work aimed to clarify the role of platelets and plasma factors in neutrophil interactions with the periodontopathogens A. actinomycetemcomitans and P. gingivalis.


METHODS
Phagocytosis, cell-cell interactions and activation of platelets and neutrophils in response to periodontopathogens were analyzed by flow cytometry, confocal microscopy and bacteria survival assay. Plasma factors, platelet signaling pathways and receptors involved in platelet-neutrophil-bacteria interactions were determined. The role of platelet and neutrophil TLR2 in phagocytosis was further evaluated in a murine TLR2 knockout model.


RESULTS
In the presence of plasma neutrophil-mediated clearance of periodontopathogens is doubled due to opsonisation of bacteria. Platelets, which become activated by periodontopathogens, further enhance clearance of bacteria by 20%, via direct interaction with neutrophils. Plasma factors (e.g. CD14) are required for platelet activation, which is mainly TLR2 dependent and results in PI3K/Akt activation. In a murine TLR2 knockout model we prove that platelet TLR2 is important for formation of platelet-neutrophil aggregates and enhanced phagocytosis of periodontopathogens. In contrast, neutrophil TLR2 is not involved in platelet-neutrophil aggregate formation but is required for efficient phagocytosis.


CONCLUSIONS
These data indicate that efficient elimination of periodontopathogens by neutrophils involves a complex interplay of plasma factors as well as platelets and requires functional TLR2. By enhancing neutrophil activation platelets contribute to immune defense but may also foster inflammation.
Institute of Physiology, Centre for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria. alice.assinger@meduniwien.ac.at
A
A
Assinger
M
M
Laky
G
G
Schabbauer
A M
AM
Hirschl
E
E
Buchberger
B R
BR
Binder
I
I
Volf
D000818:Animals; D001792:Blood Platelets / Q000276:immunology*; D015153:Blotting, Western; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D009504:Neutrophils / Q000276:immunology*; D010519:Periodontium / Q000382:microbiology*; D010587:Phagocytosis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D015539:Platelet Activation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000502:physiology*
D051195:Toll-Like Receptor 2; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt