Streptococcus pneumoniae Interactions with Macrophages and Mechanisms of Immune Evasion

Streptococcus pneumoniae persistence and survival within a host will require evasion of the dominant immune mediators targeting extracellular bacteria at each site of infection, namely mucosal immunity, macrophages, complement, and neutrophils. A wide range of different S. pneumoniae factors have been described with effects on different components of the host immune response, including the capsule, pneumolysin, and a variety of cell-surface or extracellular proteins. In this chapter, we will discuss the known mechanisms by which S. pneumoniae interacts with and evades host immunity. In particular, we will discuss in detail two striking features of S. pneumoniae biology: (1) the complexity of S. pneumoniae interactions with macrophages, including both immune evasion mechanisms and host adaptations to improve bacterial killing and control of infection; and (2) the number of mechanisms the bacterium has for preventing complement-mediated immunity and which are essential for the development of invasive infections.