title: Human platelet activation by Escherichia coli: roles for FcγRIIA and integrin αIIbβ3.
abstract: Gram-negative Escherichia coli cause diseases such as sepsis and hemolytic uremic syndrome in which thrombotic disorders can be found. Direct platelet-bacterium interactions might contribute to some of these conditions; however, mechanisms of human platelet activation by E. coli leading to thrombus formation are poorly understood. While the IgG receptor FcγRIIA has a key role in platelet response to various Gram-positive species, its role in activation to Gram-negative bacteria is poorly defined. This study aimed to investigate the molecular mechanisms of human platelet activation by E. coli, including the potential role of FcγRIIA. Using light-transmission aggregometry, measurements of ATP release and tyrosine-phosphorylation, we investigated the ability of two E. coli clinical isolates to activate platelets in plasma, in the presence or absence of specific receptors and signaling inhibitors. Aggregation assays with washed platelets supplemented with IgGs were performed to evaluate the requirement of this plasma component in activation. We found a critical role for the immune receptor FcγRIIA, αIIbβ3, and Src and Syk tyrosine kinases in platelet activation in response to E. coli. IgG and αIIbβ3 engagement was required for FcγRIIA activation. Moreover, feedback mediators adenosine 5'-diphosphate (ADP) and thromboxane A2 (TxA2) were essential for platelet aggregation. These findings suggest that human platelet responses to E. coli isolates are similar to those induced by Gram-positive organisms. Our observations support the existence of a central FcγRIIA-mediated pathway by which human platelets respond to both Gram-negative and Gram-positive bacteria.
authors.affiliation: a Institute of Cardiovascular Sciences , College of Medical and Dental Sciences, University of Birmingham , Birmingham , UK.
authors.forename: Callum N
authors.initials: CN
authors.lastname: Watson
authors.affiliation: b Cardiovascular Infection Group, Molecular and Cellular Therapeutics , Royal College of Surgeons in Ireland , Dublin , Ireland.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Kerrigan
authors.affiliation: b Cardiovascular Infection Group, Molecular and Cellular Therapeutics , Royal College of Surgeons in Ireland , Dublin , Ireland.
authors.forename: Dermot
authors.initials: D
authors.lastname: Cox
authors.affiliation: c Institute of Microbiology and Infection , College of Medical and Dental Sciences, University of Birmingham , Birmingham , UK.
authors.forename: Ian R
authors.initials: IR
authors.lastname: Henderson
authors.affiliation: a Institute of Cardiovascular Sciences , College of Medical and Dental Sciences, University of Birmingham , Birmingham , UK.
authors.forename: Steve P
authors.initials: SP
authors.lastname: Watson
authors.affiliation: a Institute of Cardiovascular Sciences , College of Medical and Dental Sciences, University of Birmingham , Birmingham , UK.|d Centre for Cardiovascular and Metabolic Research, Hull-York Medical School , University of Hull , Hull , UK.
authors.forename: Mònica
authors.initials: M
authors.lastname: Arman
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D001792:Blood Platelets / Q000276:immunology* / Q000378:metabolism*; D004926:Escherichia coli / Q000276:immunology*; D006801:Humans; D015539:Platelet Activation / Q000276:immunology; D010974:Platelet Aggregation / Q000276:immunology; D010979:Platelet Function Tests; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011485:Protein Binding; D017452:Receptors, IgG / Q000378:metabolism*; D000072377:Syk Kinase / Q000378:metabolism; D013928:Thromboxane A2 / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: C080568:Fc gamma receptor IIA; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D017452:Receptors, IgG; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D000072377:Syk Kinase; D019061:src-Family Kinases
keywords: Blood platelets; Escherichia coli; Fc gamma receptor IIA; immunity; thrombosis