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.

Higher platelet reactivity and platelet-monocyte complex formation in Gram-positive sepsis compared to Gram-negative sepsis

“…It was beyond the scope of our current study to characterize the pathways of platelet activation by the isolated pathogens. E. coli was also recently demonstrated to activate platelets in a FcγRIIa-dependent manner [29,30], although ex vivo data of platelet activation by E. coli lipopolysaccharide are conflicting [15][16][17]31]. Administration of lipopolysaccharide to healthy volunteers also does not appear to strongly activate platelets [32,33], a finding supported by our data of limited platelet activation in patients with E. coli sepsis.…”

The biology of the platelet with special reference to inflammation wound healing and immunity

“…Other platelet receptors involved in bacterial clearance are GPIb-IX and αIIbβ3 that bind Staphylococcal proteins among others and and FcγRIIA (see 33). Platelets bind to Escherichia coli (E coli) through FcγRIIA binding to IgG coating the bacteria; this leads to platelet aggregation by a secretion-and αIIbβ3dependent mechanism (135). Inflammation drives thrombosis in the liver after Salmonella infection and does so in a TLR4dependent cascade via ligation of C-type lectin-like receptor-2 (CLEC-2) on platelets by the membrane glycoprotein, podoplanin, on monocytes and kupffer cells (136).…”

Platelets kill bacteria by bridging innate and adaptive immunity via platelet factor 4 and FcγRIIA

“…Platelets interact with a wide spectrum of pathogens, including viruses, bacteria, protozoa and fungi [3][4][5][6]. Gram-negative and Gram-positive bacteria and their secreted products activate platelets, strain-specifically either directly or through plasma proteins acting as bridging molecules [7][8][9], by complex mechanisms involving the platelet Fc-receptor FccRIIA [10][11][12], glycoprotein (GP) aIIbb3, GPIba, complement receptors (e.g. gC1q-R) and Toll-like receptors (e.g.…”