Tick salivary compounds: their role in modulation of host defences and pathogen transmission

Mária Kazimírová,Iveta Štibrániová

doi:10.3389/fcimb.2013.00043

Abstract

Ticks require blood meal to complete development and reproduction. Multifunctional tick salivary glands play a pivotal role in tick feeding and transmission of pathogens. Tick salivary molecules injected into the host modulate host defence responses to the benefit of the feeding ticks. To colonize tick organs, tick-borne microorganisms must overcome several barriers, i.e., tick gut membrane, tick immunity, and moulting. Tick-borne pathogens co-evolved with their vectors and hosts and developed molecular adaptations to avoid adverse effects of tick and host defences. Large gaps exist in the knowledge of survival strategies of tick-borne microorganisms and on the molecular mechanisms of tick-host-pathogen interactions. Prior to transmission to a host, the microorganisms penetrate and multiply in tick salivary glands. As soon as the tick is attached to a host, gene expression and production of salivary molecules is upregulated, primarily to facilitate feeding and avoid tick rejection by the host. Pathogens exploit tick salivary molecules for their survival and multiplication in the vector and transmission to and establishment in the hosts. Promotion of pathogen transmission by bioactive molecules in tick saliva was described as saliva-assisted transmission (SAT). SAT candidates comprise compounds with anti-haemostatic, anti-inflammatory and immunomodulatory functions, but the molecular mechanisms by which they mediate pathogen transmission are largely unknown. To date only a few tick salivary molecules associated with specific pathogen transmission have been identified and their functions partially elucidated. Advanced molecular techniques are applied in studying tick-host-pathogen interactions and provide information on expression of vector and pathogen genes during pathogen acquisition, establishment and transmission. Understanding the molecular events on the tick-host-pathogen interface may lead to development of new strategies to control tick-borne diseases.

Highlights

Ticks are obligate blood feeding ectoparasites of a wide range of vertebrates
In comparison with syringe inoculation of B. burgdorferi, IL-4 produced in host draining lymph nodes following tick bites greatly inhibited the production of antiborrelial IgG2a antibodies (Christe et al, 2000). These findings were further supported by experiments in which a B cell inhibitory protein (BIP) from I. ricinus salivary glands suppressed B lymphocyte proliferation induced by the B. burgdorferi outer surface protein C (OspC), suggesting that BIP may play an important role in enhancing B. burgdorferi transmission by the tick (Hannier et al, 2003)
Ticks modulate host responses at the site of their attachment to the hosts by a wide range of salivary molecules and, as a result, they create an environment which is favorable for both the feeding ticks as well as transmission of the microorganisms that ticks may carry

Summary

Introduction

Ticks are obligate blood feeding ectoparasites of a wide range of vertebrates (amphibians, reptiles, birds, mammals). An immunomodulatory www.frontiersin.org serpin identified in the salivary glands of I. ricinus was the first ectoparasite serpin that was reported to both interfere with host haemostasis and the immune response and increase platelet adhesion, the contact phase-activated pathway of coagulation and fibrinolysis (Prevot et al, 2006).

Results

Conclusion