Role of capsule in K. pneumoniae virulence. Role of capsule in K. pneumoniae virulence. A number of different functions for capsule have been delineated for K. pneumoniae virulence. First, capsule prevents phagocytosis and opsonophagocytosis of the bacteria by immune cells. Second, it hinders the bactericidal action of antimicrobial peptides such as human beta defensins 1 to 3 and lactoferrin by binding these molecules distal from the outer membrane. Third, it blocks complement components, such as C3, from interacting with the membrane, thus preventing complement-mediated lysis and opsonization. Finally, it averts the fulminant activation of the immune response, as measured by decreased reactive oxygen species (ROS), IL-8, IL-6, and TNF-α production, by assisting in the activation of a NOD-dependent pathway and shielding LPS from recognition by immune cell receptors. Michelle K. Paczosa, and Joan Mecsas Microbiol. Mol. Biol. Rev. 2016; doi:10.1128/MMBR.00078-15