Tick Innate Immunity

Abstract

Ticks are blood feeding parasites transmitting a wide variety of pathogens to their vertebrate hosts. The vector competence of ticks is tightly linked with their immune system. Despite its importance, our knowledge of tick innate immunity is still LQDGHTXDWH DQG WKH OLPLWHG QXPEHU RI VXI¿FLHQWO\ FKDUDFWHUL]HG LPPXQH PROHFXOHV and cellular reactions are dispersed across numerous tick species. The phagocytosis of microbes by tick hemocytes seems to be coupled with a primitive complement-like V\VWHP ZKLFK SRVVLEO\ LQYROYHV VHOIQRQVHOI UHFRJQLWLRQ E\ ¿EULQRJHQUHODWHG lectins and the action of thioester-containing proteins. Ticks do not seem to possess a pro-phenoloxidase system leading to melanization and also coagulation of tick hemolymph has not been experimentally proven. They are capable of defending themselves against microbial infection with a variety of antimicrobial peptides comprising lysozymes, defensins and molecules not found in other invertebrates. Virtually nothing is known about the signaling cascades involved in the regulation of tick antimicrobial immune responses. Midgut immunity is apparently the decisive factor of tick vector competence. The gut content is a hostile environment for ingested microbes, which is mainly due to the antimicrobial activity of hemoglobin fragments generated by the digestion of the host blood as well as other antimicrobial peptides. Reactive oxygen species possibly also play an important role in the tick-pathogen interaction. The recent release of the Ixodes scapularis genome and the feasibility of RN R R A interference in ticks promise imminent and substantial progress in tick innate immunity research.Invertebrate Immunity, edited by Kenneth Söderhäll.

Antiviral responses of arthropod vectors: an update on recent advances

“…A comparative genomic study of D. melanogaster, A. gambiae and A. aegypti examined the evolutionary dynamics of immunity genes in higher insects [126]. In ticks, knowledge about immunity pathways is generally very limited; however, immune responses against bacteria have been studied in some detail [63,74] and the knowledge gained about bacterial defences may provide a basis for studies on antiviral defence mechanisms.…”

“…However, for I. scapularis there are a number of putative Toll receptors in the published genome [46] and also orthologues of REL1 and Cactus [63]. Their role in immune defences against bacterial or viral infection remains unknown.…”

“…Whether this pathway plays a role in virus infection of ticks remains unknown. In addition, a relatively large number of AMPs have been found in ticks and some of them, such as defensins, have been well characterised; however, their regulation remains unclear and, in particular, nothing is known about their antiviral effects (reviewed by [63]). …”

“…The latter result may have been due to the small amounts of haemolymph used or due to a PO inhibitory factor present in the samples. However, no orthologue of PO could be found in the I. scapularis genome [63] indicating that there is a possibility that ixodid ticks have lost this mechanism (argasid ticks are ancestral to ixodid ticks) or that a different protein may have evolved to have a comparable function to PO.…”

Efeitos da infecção por Rickettsia rickettsii sobre o perfil de expressão gênica do carrapato vetor Amblyomma cajennense.

“…Como consequência deste longo período de alimentação, uma grande diversidade de patógenos pode ser transmitida ao hospedeiro durante o repasto sanguíneo Kopácek et al, 2010).…”