Iripin-3, a New Salivary Protein Isolated From Ixodes ricinus Ticks, Displays Immunomodulatory and Anti-Hemostatic Properties In Vitro

Front Immunol. 2021 Mar 1:12:626200. doi: 10.3389/fimmu.2021.626200. eCollection 2021.


Tick saliva is a rich source of pharmacologically and immunologically active molecules. These salivary components are indispensable for successful blood feeding on vertebrate hosts and are believed to facilitate the transmission of tick-borne pathogens. Here we present the functional and structural characterization of Iripin-3, a protein expressed in the salivary glands of the tick Ixodes ricinus, a European vector of tick-borne encephalitis and Lyme disease. Belonging to the serpin superfamily of protease inhibitors, Iripin-3 strongly inhibited the proteolytic activity of serine proteases kallikrein and matriptase. In an in vitro setup, Iripin-3 was capable of modulating the adaptive immune response as evidenced by reduced survival of mouse splenocytes, impaired proliferation of CD4+ T lymphocytes, suppression of the T helper type 1 immune response, and induction of regulatory T cell differentiation. Apart from altering acquired immunity, Iripin-3 also inhibited the extrinsic blood coagulation pathway and reduced the production of pro-inflammatory cytokine interleukin-6 by lipopolysaccharide-stimulated bone marrow-derived macrophages. In addition to its functional characterization, we present the crystal structure of cleaved Iripin-3 at 1.95 Å resolution. Iripin-3 proved to be a pluripotent salivary serpin with immunomodulatory and anti-hemostatic properties that could facilitate tick feeding via the suppression of host anti-tick defenses. Physiological relevance of Iripin-3 activities observed in vitro needs to be supported by appropriate in vivo experiments.

Keywords: Ixodes ricinus; X-ray crystallography; adaptive immunity; blood coagulation; inflammation; saliva; serpin; tick.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptive Immunity / drug effects*
  • Animals
  • Anticoagulants / isolation & purification
  • Anticoagulants / pharmacology*
  • Blood Coagulation / drug effects*
  • Cell Proliferation / drug effects
  • Cells, Cultured
  • Cytokines / metabolism
  • Guinea Pigs
  • Humans
  • Immunologic Factors / isolation & purification
  • Immunologic Factors / pharmacology*
  • Insect Proteins / isolation & purification
  • Insect Proteins / pharmacology*
  • Ixodes / metabolism*
  • Lymphocyte Activation / drug effects
  • Lymphocytes / drug effects
  • Lymphocytes / immunology
  • Lymphocytes / metabolism
  • Mice
  • Mice, Inbred C3H
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Protease Inhibitors / isolation & purification
  • Protease Inhibitors / pharmacology
  • Rabbits
  • Saliva / metabolism*
  • Salivary Proteins and Peptides / isolation & purification
  • Salivary Proteins and Peptides / pharmacology*
  • Spleen / drug effects
  • Spleen / immunology
  • Spleen / metabolism


  • Anticoagulants
  • Cytokines
  • Immunologic Factors
  • Insect Proteins
  • Protease Inhibitors
  • Salivary Proteins and Peptides