Legionella pathogenicity is due to?

Failure of oxidative burst REF: Harrison's 17th edition, chapter 141 Pathogenesis of legionella infection Legionella enters the lungs through aspiration or direct inhalation. Attachment to host cells is mediated by bacterial type IV pili, heat-shock proteins, and the major outer-membrane protein. Because the organisms possess pili that may mediate adherence to respiratory tract epithelial cells, conditions that impair mucociliary clearance, including cigarette smoking, lung disease, or alcoholism, predispose to Legionnaires' disease. Cell-mediated immunity is the primary mechanism of host defense against Legionella, as it is against other intracellular pathogens. Thus Legionnaires' disease is more common and its manifestations are more severe among patients with depressed cell-mediated immunity Alveolar macrophages readily phagocytose Legionella. The attachment of the bacteria to phagocytes is mediated Fc receptors and complement receptors, which attach to the bacterial major outer-membrane protein. Binding to these receptors promotes phagocytosis but fails to trigger an oxidative burst.