At least 12 proteins are known that do this. Factor I inactivates C3b. Disorders of the Complement System With so many proteins involved, it is not surprising that inherited deficiencies of one or another are sometimes encountered in humans. An inherited deficiency of C3 predisposes the person to frequent bouts of bacterial infections. This emphasizes the important role of the complement system in clearing away antigen-antibody complexes.
Patients are at risk of occasional explosive triggering of the complement system.