title: The paralogous salivary anti-complement proteins IRAC I and IRAC II encoded by Ixodes ricinus ticks have broad and complementary inhibitory activities against the complement of different host species.
abstract: Several observations suggest that inhibition of the host complement alternative pathway by Ixodes tick saliva is crucial to achieve blood feeding. We recently described two paralogous anti-complement proteins called Ixodes ricinus anti-complement (IRAC) proteins I and II co-expressed in I. ricinus salivary glands. Phylogenetic analyses suggested that these sequences were diversifying by a process of positive Darwinian selection, possibly leading to molecules with different biological properties. In the present study, we tested the hypothesis that each paralogue may have different inhibitory activities against the complement of different natural host species, thereby contributing to broaden the host range of I. ricinus ticks. IRAC I and IRAC II were tested against the complement of eight I. ricinus natural host species (six mammals and two birds). The results demonstrate that IRAC I and IRAC II have broad and complementary inhibition activities against the complement of different host species. This report is the first description of paralogous anti-complement molecules encoded by a pathogen with broad and complementary inhibitory activities against the complement of different host species.
authors.forename: Hélène
authors.initials: H
authors.lastname: Schroeder
authors.forename: Virginie
authors.initials: V
authors.lastname: Daix
authors.forename: Laurent
authors.initials: L
authors.lastname: Gillet
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Renauld
authors.forename: Alain
authors.initials: A
authors.lastname: Vanderplasschen
mesh_terms: D000818:Animals; D001717:Birds; D003169:Complement Inactivator Proteins / Q000378:metabolism*; D003170:Complement Pathway, Alternative; D003165:Complement System Proteins / Q000276:immunology*; D006801:Humans; D018884:Ixodes / Q000378:metabolism* / Q000472:pathogenicity; D008322:Mammals; D013045:Species Specificity
chemical_list: D003169:Complement Inactivator Proteins; D003165:Complement System Proteins