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 (PubMed:27018802, PubMed:31871188). 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.