A combined transcriptomic approach to identify candidates for an anti-tick vaccine blocking B. afzelii transmission

Jos J A Trentelman,Julen Tomás-Cortázar,Joppe W Hovius,Sazzad Mahmood,Hein Sprong,Diego Barriales,Juan Anguita,Radek Sima,Ondrej Hajdusek,Veronika Urbanova,Nicolas Krezdorn,Katsuhisa Takumi,Petr Kopacek,Joe M Butler,Michelle J Klouwens,Peter Winter

doi:10.1038/s41598-020-76268-y

Abstract

Ixodes ricinus is the vector for Borrelia afzelii, the predominant cause of Lyme borreliosis in Europe, whereas Ixodes scapularis is the vector for Borrelia burgdorferi in the USA. Transcription of several I. scapularis genes changes in the presence of B. burgdorferi and contributes to successful infection. To what extend B. afzelii influences gene expression in I. ricinus salivary glands is largely unknown. Therefore, we measured expression of uninfected vs. infected tick salivary gland genes during tick feeding using Massive Analysis of cDNA Ends (MACE) and RNAseq, quantifying 26.179 unique transcripts. While tick feeding was the main differentiator, B. afzelii infection significantly affected expression of hundreds of transcripts, including 465 transcripts after 24 h of tick feeding. Validation of the top-20 B. afzelii-upregulated transcripts at 24 h of tick feeding in ten biological genetic distinct replicates showed that expression varied extensively. Three transcripts could be validated, a basic tail protein, a lipocalin and an ixodegrin, and might be involved in B. afzelii transmission. However, vaccination with recombinant forms of these proteins only marginally altered B. afzelii infection in I. ricinus-challenged mice for one of the proteins. Collectively, our data show that identification of tick salivary genes upregulated in the presence of pathogens could serve to identify potential pathogen-blocking vaccine candidates.

Highlights

Ixodes ticks are small parasitic arthropods that feed on the blood of vertebrate hosts
As with all biological processes, the expression, translation and secretion of tick salivary gland proteins (TSGPs) is a dynamic process. The expression of these TSGPs is highly upregulated during the tick feeding p rocess[21,22,23,24], but it is known that infection with B. burgdorferi s.s. induces alterations in gene expression that contribute to the successful infection of the h ost[13,14,15,25,26,27,28,29]
Salivary gland and whole body RNA was isolated from B. afzelii CB43-infected I. ricinus nymphs and uninfected I. ricinus nymphs from the same parental lineage fed for 0, 24 or 72 h

Summary

Introduction

Ixodes ticks are small parasitic arthropods that feed on the blood of vertebrate hosts. As with all biological processes, the expression, translation and secretion of TSGPs is a dynamic process The expression of these TSGPs is highly upregulated during the tick feeding p rocess[21,22,23,24], but it is known that infection with B. burgdorferi s.s. induces alterations in gene expression that contribute to the successful infection of the h ost[13,14,15,25,26,27,28,29]. These multi-gene families are thought to be the result of gene duplication early in evolution[31]

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