title: Platelet-borne complement proteins and their role in platelet-bacteria interactions.
abstract: Essentials Platelets play an important role in pathogen recognition. Platelets contain several complement factors and can interact with E. coli. Platelet's complement protein C3 differs from plasmatic C3 in its electrophoretic mobility. Upon contact with bacteria, platelets are activated and can enhance complement activation.
  
  
  
  Background The role of platelets in immune defense is increasingly being recognized. Platelets bind complement proteins from plasma, initiate complement activation, and interact with bacteria. However, the contribution of platelets to complement-mediated defense against bacterial infections is not known in detail. Objectives To assess platelet interactions with Escherichia coli strains, and evaluate the contributions of platelet complement proteins to host defense. Methods We studied the cell-cell interactions of a pathogenic and a non-pathogenic E. coli strain with platelet concentrates, washed platelets and manually isolated platelets by flow cytometry and ELISA. The presence of complement proteins and complement RNA in megakaryocytes and platelets was analyzed by PCR, RT-PCR, confocal microscopy, and western blotting. Results Incubation with E. coli leads to platelet activation, as indicated by the expression of CD62P and CD63 on the platelet surface. RNA and protein analyses show that megakaryocytes and platelets contain complement C3, and that platelet C3 migrates differently on polyacrylamide gels than plasmatic C3. Activation of platelets by bacteria leads to translocation of C3 to the cell surface. This translocation is not induced by thrombin receptor activating peptide or lipopolysaccharide. Interaction of platelets with E. coli occurs even in the absence of plasma proteins, and is independent of platelet toll-like receptor 4 and α2bβ3(glycoprotein IIbIIIa). Conclusion Platelets contain a specific form of C3. Importantly, they can modulate immune defense against bacteria by enhancing plasmatic complement activation.
authors: Department of Laboratory Medicine, Medical University, Vienna, Austria.
authors: I
authors: I
authors: Arbesu
authors: Department of Laboratory Medicine, Medical University, Vienna, Austria.
authors: M
authors: M
authors: Bucsaiova
authors: Center for Biomedical Technology, Donau-Universität Krems, Krems, Austria.|Department of Blood Serology and Transfusion Medicine, Medical University of Vienna, Vienna, Austria.
authors: M B
authors: MB
authors: Fischer
authors: Department of Laboratory Medicine, Medical University, Vienna, Austria.
authors: C
authors: C
authors: Mannhalter
mesh_terms: D001792:Blood Platelets / Q000276:immunology* / Q000382:microbiology*; D002462:Cell Membrane; D002469:Cell Separation; D003167:Complement Activation; D003176:Complement C3 / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D004927:Escherichia coli Infections / Q000097:blood / Q000276:immunology*; D005312:Fetal Blood / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D007107:Immune System; D007113:Immunity, Innate; D008533:Megakaryocytes / Q000166:cytology; D019007:P-Selectin / Q000378:metabolism; D015539:Platelet Activation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D060149:Tetraspanin 30 / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism
chemical_list: C038245:C3 protein, human; C554586:CD63 protein, human; D003176:Complement C3; D019007:P-Selectin; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C546937:SELP protein, human; C495345:TLR4 protein, human; D060149:Tetraspanin 30; D051197:Toll-Like Receptor 4
keywords: Gram-negative bacteria; complement; infection; megakaryocytes; platelets