Novel immunomodulators from hard ticks selectively reprogramme human dendritic cell responses

PLoS Pathog. 2013;9(6):e1003450. doi: 10.1371/journal.ppat.1003450. Epub 2013 Jun 27.

Abstract

Hard ticks subvert the immune responses of their vertebrate hosts in order to feed for much longer periods than other blood-feeding ectoparasites; this may be one reason why they transmit perhaps the greatest diversity of pathogens of any arthropod vector. Tick-induced immunomodulation is mediated by salivary components, some of which neutralise elements of innate immunity or inhibit the development of adaptive immunity. As dendritic cells (DC) trigger and help to regulate adaptive immunity, they are an ideal target for immunomodulation. However, previously described immunoactive components of tick saliva are either highly promiscuous in their cellular and molecular targets or have limited effects on DC. Here we address the question of whether the largest and globally most important group of ticks (the ixodid metastriates) produce salivary molecules that specifically modulate DC activity. We used chromatography to isolate a salivary gland protein (Japanin) from Rhipicephalus appendiculatus ticks. Japanin was cloned, and recombinant protein was produced in a baculoviral expression system. We found that Japanin specifically reprogrammes DC responses to a wide variety of stimuli in vitro, radically altering their expression of co-stimulatory and co-inhibitory transmembrane molecules (measured by flow cytometry) and their secretion of pro-inflammatory, anti-inflammatory and T cell polarising cytokines (assessed by Luminex multiplex assays); it also inhibits the differentiation of DC from monocytes. Sequence alignments and enzymatic deglycosylation revealed Japanin to be a 17.7 kDa, N-glycosylated lipocalin. Using molecular cloning and database searches, we have identified a group of homologous proteins in R. appendiculatus and related species, three of which we have expressed and shown to possess DC-modulatory activity. All data were obtained using DC generated from at least four human blood donors, with rigorous statistical analysis. Our results suggest a previously unknown mechanism for parasite-induced subversion of adaptive immunity, one which may also facilitate pathogen transmission.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptive Immunity / drug effects
  • Adaptive Immunity / genetics
  • Adaptive Immunity / immunology
  • Animals
  • Arthropod Proteins / genetics
  • Arthropod Proteins / immunology*
  • Arthropod Proteins / pharmacology
  • Cell Differentiation / drug effects
  • Cell Differentiation / genetics
  • Cell Differentiation / immunology
  • Cell Line
  • Cytokines / genetics
  • Cytokines / immunology
  • Dendritic Cells / immunology*
  • Dendritic Cells / pathology
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / genetics
  • Gene Expression Regulation / immunology
  • Humans
  • Immunologic Factors / genetics
  • Immunologic Factors / immunology*
  • Immunologic Factors / pharmacology
  • Monocytes / immunology*
  • Monocytes / pathology
  • Recombinant Proteins / genetics
  • Recombinant Proteins / immunology
  • Recombinant Proteins / pharmacology
  • Rhipicephalus / genetics
  • Rhipicephalus / immunology*
  • Salivary Proteins and Peptides / genetics
  • Salivary Proteins and Peptides / immunology*
  • Salivary Proteins and Peptides / pharmacology

Substances

  • Arthropod Proteins
  • Cytokines
  • Immunologic Factors
  • Recombinant Proteins
  • Salivary Proteins and Peptides

Grant support

This work was funded by the Natural Environment Research Council (http://www.nerc.ac.uk/); the European Union Sixth Framework Programme (http://cordis.europa.eu/lifescihealth/home.html via the DC-THERA Network of Excellence, Project No. LSHB-CT-2004-512074); and, from Sept 2010 to Sept 2011, by IXO Therapeutics Ltd. (http://www.ixo-ltd.com/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.