Platelets: at the nexus of antimicrobial defence

Platelets have multiple direct and indirect functions that integrate innate and adaptive antimicrobial host defences.Platelets actively sense signals of tissue injury and microbial infection via an array of constitutive and inducible membrane receptors.Activated platelets deliver antimicrobial effector molecules, such as kinocidins and platelet microbicidal proteins, to sites of tissue injury or infection and in the bloodstream.Platelet products inhibit viral, bacterial, fungal and protozoan pathogens; for example, new studies demonstrate the importance of kinocidins in human defence against malaria and HIV-1.Platelet interactions with T cells, B cells, neutrophils and other immune system components connect innate and adaptive immunity to promote optimal host defence against infection.Thrombocytopenia and platelet antagonists that inhibit the antimicrobial roles of platelets may be risk factors for infection.