title: The role of P-selectin in the immune destruction of platelets.
abstract: Antibody-mediated platelet destruction is a poorly understood process, although several lines of evidence suggest that Fcgamma receptor (FcgammaR)-expressing splenic macrophages may be involved. In this study, chemiluminescence (CL) was used to measure the in vitro metabolic response of human monocytes to platelets sensitized with a human immunoglobulin (Ig)G1 recombinant antihuman platelet antigen-1a (anti-HPA-1a) antibody (B2G1; P-hrIgG1). CL responses were inhibited, but not abrogated, in the presence of 10 micro g/ml human IgG or murine IgG2a, suggesting that FcgammaRI was principally involved. Experiments to determine the effect of Fab fragments to FcgammaRII found that CL responses to P-hrIgG1 were significantly enhanced, indicating that crosslinking of monocyte FcgammaRII by platelet-bound hIgG may modulate concomitant activation by FcgammaRI. Several observations suggested that the CL responses to P-IgG were dependent on the activation of resting platelets during their co-culture with monocytes and their subsequent P-selectin-mediated adhesion. First, the magnitude of the CL response was related to the level of P-selectin expression following platelet activation with alpha-thrombin. Second, CL responses were inhibited in the presence of antibodies that block the binding of P-selectin to P-selectin glycoprotein ligand-1 but not when platelets were pretreated and then washed. Third, the addition of anti-HPA-1a to monocytes from HPA-1a-negative donors preincubated with HPA-1a-positive platelets resulted in rapid CL responses. Finally, PGI2 inhibited the CL response to resting P-hrIgG1. Thus, evidence is presented that the interaction of human monocytes with P-hrIgG1 is mediated by FcgammaRI, modulated via FcgammaRII, and enhanced by the presence of P-selectin on the platelet membrane.
authors.affiliation: Bristol Institute for Transfusion Sciences, Bristol, UK.
authors.forename: Craig P
authors.initials: CP
authors.lastname: Turner
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Hadley
mesh_terms: D016824:Antigens, Human Platelet / Q000276:immunology; D001792:Blood Platelets / Q000276:immunology*; D002448:Cell Adhesion; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D039661:Integrin beta3; D009000:Monocytes / Q000276:immunology; D019007:P-Selectin / Q000502:physiology*; D015539:Platelet Activation; D017452:Receptors, IgG / Q000037:antagonists & inhibitors / Q000276:immunology
chemical_list: D016824:Antigens, Human Platelet; C061248:ITGB3 protein, human; D007074:Immunoglobulin G; D039661:Integrin beta3; D019007:P-Selectin; D017452:Receptors, IgG