Complement inhibitor (PubMed:27018802). Prevents complement-mediated C5 activation by binding to C5 (PubMed:27018802). Binds C5 at a different binding site than the other tick complement inbibitors OmCI and CirpT1, and the drug eculizumab (By similarity). Inhibits complement in human and guinea pig but not in other species tested (rabbit, rat, mouse, and pig) (PubMed:27018802). Expressed by salivary glands. Belongs to the RaCI family.