Our studies are concerned with the role of the complement system in the host's defense against infection. We have been attempting to identify the biochemical component of gram-positive bacteria that activates the alternative pathway. We have also been studying where and how nascent C3b fixes to the bacterial surface. Finally, we are also studying the way in which the complement system participates in viral infections both to serve the host in its defense against the virus as well as harm the host in the generation of immunopathologic damage during the viral infection.