Human complement regulators: a major target for pathogenic microorganisms

The C3 convertases of the human complement system are controlled by fluid-p hase and membrane proteins in the RCA (regulators of complement activation) family. Accumulated data show that many pathogenic microorganisms interact with these complement regulators. Recent advances in this field include de termination of the crystal structure of the binding domains in the measles virus receptor CD46 and identification of a CD46 transgenic mouse line that is sensitive to measles virus. Moreover, recent findings support the hypot hesis that pathogenic bacteria binding fluid-phase RCA proteins exploit the se proteins to escape complement attack. These studies provide novel insigh t into the interplay between pathogens and the innate immune system and may have implications for the plans to use animals expressing an RCA protein f or xenotransplantation.