Staphylococcal superantigen-like 5 activates platelets and supports platelet adhesion under flow conditions, which involves glycoprotein Ibalpha and alpha IIb beta 3.
OBJECTIVE
Staphylococcal superantigen-like 5 (SSL5) is an exoprotein secreted by Staphylococcus aureus that has been shown to inhibit neutrophil rolling over activated endothelial cells via a direct interaction with P-selectin glycoprotein ligand 1 (PSGL-1).


RESULTS
When purified recombinant SSL5 was added to washed platelets in an aggregometry set-up, complete and irreversible aggregation was observed. Proteolysis of the extracellular part of GPIb alpha or the addition of dRGDW abrogated platelet aggregation. When a mixture of isolated platelets and red cells was perfused over immobilized SSL5 at a shear rate of 300 s(-1), stable platelet aggregates were observed, and platelet deposition was substantially reduced after proteolysis of GPIb or after addition of dRGDW. SSL5 was shown to interact with glycocalicin, a soluble GPIb alpha fragment, and binding of SSL5 to platelets resulted in GPIb-mediated signal transduction as evidenced by translocation of 14-3-3 zeta. In addition, SSL5 was shown to interact with endothelial cell matrix (ECM) and this interaction enhanced aggregation of platelets from whole blood to this ECM.


CONCLUSIONS
SSL5 activates and aggregates platelets in a GPIb alpha-dependent manner, which could be important in colonization of the vascular bed and evasion of the immune system by S. aureus.
de Haas
C J C
CJ
Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Weeterings
C
C
Vughs
M M
MM
de Groot
P G
PG
Van Strijp
J A
JA
Lisman
T
T
D001792:Blood Platelets / Q000166:cytology / Q000382:microbiology*; D002478:Cells, Cultured; D004912:Erythrocytes / Q000166:cytology; D010477:Perfusion; D015539:Platelet Activation / Q000187:drug effects / Q000276:immunology*; D010973:Platelet Adhesiveness / Q000187:drug effects / Q000276:immunology*; D010974:Platelet Aggregation / Q000187:drug effects / Q000276:immunology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D013210:Staphylococcus / Q000276:immunology*; D018089:Superantigens / Q000494:pharmacology / Q000502:physiology*
D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D018089:Superantigens