Abstract
Ixodes ricinus is the main vector of tick-borne diseases in Europe. An immunization trial of calves with soluble extracts of I. ricinus salivary glands (SGE) or midgut (ME) previously showed a strong response against subsequent tick challenge, resulting in diminished tick feeding success. Immune sera from these trials were used for the co-immunoprecipitation of tick tissue extracts, followed by LC-MS/MS analyses. This resulted in the identification of 46 immunodominant proteins that were differentially recognized by the serum of immunized calves. Some of these proteins had previously also drawn attention as potential anti-tick vaccine candidates using other approaches. Selected proteins were studied in more detail by measuring their relative expression in tick tissues and RNA interference (RNAi) studies. The strongest RNAi phenotypes were observed for MG6 (A0A147BXB7), a protein containing eight fibronectin type III domains predominantly expressed in tick midgut and ovaries of feeding females, and SG2 (A0A0K8RKT7), a glutathione-S-transferase that was found to be upregulated in all investigated tissues upon feeding. The results demonstrated that co-immunoprecipitation of tick proteins with host immune sera followed by protein identification using LC-MS/MS is a valid approach to identify antigen–antibody interactions, and could be integrated into anti-tick vaccine discovery pipelines.
Highlights
Ixodes ricinus is a three-host ixodid tick species that is widely distributed in Western Europe
Besides their capacity to transmit a wide variety of pathogens, it was recently demonstrated that the saliva of I. ricinus contained galactose-α-1,3-galactose (α-Gal)-carrying proteins, which are associated with the induction of an anti-α-Gal immune response in humans and may result in red meat allergy [2,3]
The artificial feeding of blood and plasma of animals immunized with tick midgut extracts showed that antibodies, in the presence of complement, were able to damage tick gut cells, thereby reproducing some of the detrimental effects observed in R. microplus ticks fed directly on immunized cows [11]
Summary
Ixodes ricinus is a three-host ixodid tick species that is widely distributed in Western Europe It is the predominant vector of several pathogens of medical and veterinary relevance, including tick-borne encephalitis virus (TBEV), Borrelia burgdorferi sensu lato (the causal agent of Lyme borreliosis), and Babesia divergens [1]. Anti-tick vaccines targeting the common cattle tick Rhipicephalus microplus have been successfully developed and commercialized in the last century [8,9] These vaccines are based on a single recombinant antigen, Bm86, a protein located in the microvilli of the tick midgut. The identification of antibody–antigen complexes responsible for disrupting tick feeding could be of relevance in the identification of tickprotective antigens
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