S Pneumoniae virulence Factors Polysaccharide Capsule that prevents phagocytosis by the hosts immune cells surface proteins that prevent the activation of complement-mediated opsonization pilli that enable s pneumoniae to attach to epithelial cells in the upper respiratory tractS. Pneumoniae Virulence Factors Polysaccharaide Capsule surface proteins pili • that prevents phagocytosis by the host's immune cells • that prevent the activation of complement-mediated opsonization. • that enable to attach to epithelial cells in the upper respiratory tract S. pneumoniae