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Publisher Summary This chapter focuses on what is known about the influenza hemagglutinin and on the data to support the central role of influenza hemagglutinin in neutrophil activation and deactivation by the virus. The chapter discusses the nature of the receptor to which hemagglutinin binds and explains how it may serve as the trigger for the distinctive neutrophil response cascade. Natural immunity is characterized by effector cells and soluble factors that do not require specific prolonged induction for their functions and more specifically do not require opsonization of their target. This antibody-independent phagocytosis of pathogens has been characterized as lectinophagocytosis and serves as a basic model for examining phagocyte-mediated natural immune reactions. Whether the lectin is on the particle or on the cell, the binding is mediated by carbohydrate specificity. Many bacterial species express surface hemagglutinins or lectins, which allow binding to animal cells. Influenza A virus (IAV) attaches to a membrane receptor that subserves some other purpose in host defense. A growing list of major viruses utilizes important, conserved cellular membrane proteins involved in host defense and/or in intercellular recognition as their binding site. Although various viruses bind to protein structures directly, rather than to carbohydrate as with IAV, a common functional theme may emerge once specific IAV-binding sites are characterized on the neutrophil. |
