Complement and the host's defense against the pneumococcus.

The complement system plays a critical role in resistance to Streptococcus pneumoniae. In the last two decades, a great deal of new knowledge has been generated on both the complement system and on the pneumococcus. Not only has this new knowledge helped produce a better understanding of how the complement system serves the host in its defense against S. pneumoniae, but in a more general fashion, the lessons learned from the interaction of complement and the pneumococcus have also provided insight into how the complement system functions in the defense of the host against a wide variety of other microorganisms. The following review will attempt to summarize current knowledge about the complement system, how it interacts at the molecular level with the pneumococcus, the biologic consequences of that interaction, and their significance in pneumococcal infections.