Activated platelets kill Staphylococcus aureus, but not Streptococcus pneumoniae—The role of FcγRIIa and platelet factor 4/heparinantibodies

Heparin induced thrombocytopenia (HIT) is likely a misdirected bacterial host defense mechanism. Platelet factor 4 (PF4) binds to polyanions on bacterial surfaces exposing neo-epitopes to which HIT antibodies bind. Platelets are activated by the resulting immune complexes via FcγRIIA, release bactericidal substances, and kill Gram-negative Escherichia coli.To assess the role of PF4, anti-PF4/H antibodies and FcγRIIa in killing of Gram-positive...