RICYSTVACANT2010

"Exploring the salivary transcriptome of Ixodes ricinus, the Lyme disease vector in Europe, and the potential role of its cystatins in pathogen transmission"

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 Obiettivo del progetto (Objective)

'Ixodes ricinus abundance and its infection prevalence with Borrelia burgdorferi s.l. (the Lyme disease agent) have led to an increased risk of human exposure to tick bites and Borrelia infection in Europe. Acaricide based control of this vector has caused serious repercussions, thus raising the importance for the development of anti-tick vaccines. My previous work has demonstrated that guinea pigs vaccinated with a salivary cystatin of Ixodes scapularis, the Lyme vector in the USA, are partially protected against tick blood feeding and that the same protein facilitates Borrelia transmission as well. I. ricinus cystatin ortho-/homologues are not studied yet, partially due to the limited genomic information for this tick. Hence, this study aims to enrich our knowledge of I. ricinus salivary transcripts by considering the entire complex tick lifecycle and by performing massive 454 pyrosequencing, a relatively novel, highly efficient and cost effective technology. In parallel, library screens will be carried out to identify I. ricinus secreted cystatins. Their tissue specificity and abundance will be estimated, while gene silencing will evaluate their contribution to tick feeding success. Recombinant cystatins will be 1) biochemically characterised for their inhibitory effect on different cysteine proteases and 2) tested for their role in vertebrate host immunomodulation/pathogen transmission. Next, vaccination studies will investigate their potential to provide protection against I. ricinus and/or Lyme disease transmission. Overall, the proposed project is expected to enhance my collaboration with the scientific community in the United States and Europe, thus promoting the transfer of knowledge and technology in the field of tick functional genomics. It is also expected to reveal novel candidate salivary antigens for anti-tick vaccine development and thus to contribute towards a concerted effort for the control of a vector borne disease in Europe.'

Introduzione (Teaser)

Lyme disease is transmitted by Ixodes ricinus, the castor bean tick. As tick salivary secretion assists pathogen transmission, tick salivary components can be targeted in anti-tick vaccine development.

Descrizione progetto (Article)

The abundance of I. ricinus tick in Europe and its infection with Borrelia burgdorferi leads to increased risk of human exposure to Borrelia infection. The EU-funded RICYSTVACANT2010 project aimed at studying the components of tick saliva participating in bacterial transmission. Prior to this effort, scientists had very limited knowledge of I. ricinus genes expressed in the pathogen transmission interface of tick salivary glands. The project used a high-throughput approach to identify the expressed transcripts.

RICYSTVACANT2010 deposited more than 27 500 transcript sequences in the GenBank as originating from the tick I. ricinus, providing extensive information on its gene expression regulation. It described the transcription patterns of 27 500 genes specific to the tissue and developmental stage, as well as a function of tick feeding time. The constructed transcriptome database allowed identification of approximately 1 500 tick proteins found in the pathogen transmission interface using proteomics.

In addition to the transcriptome and proteome databases, library screens identified I. ricinus-secreted cystatins. Tick cystatins may work as 'silent' antigens for the development of anti-tick vaccines. The scientists cloned 15 cystatin genes and estimated their tissue specificity using real-time quantitative polymerase chain reaction as a function of tick feeding time. Four recombinant cystatins were successfully overexpressed in a prokaryotic system, characterised for their inhibitory effect on cysteine proteases and tested for their role in human immunomodulation.

Pharmacological characterisation of the recombinant cystatins suggested their immunomodulatory function. One of the I. ricinus cystatins was able to ameliorate the symptoms of experimental asthma in mice.

All the produced data are publicly available to support additional research projects targeting the specific tick and its pathogen transmission life cycle.