The structure and function of Iristatin, a novel immunosuppressive tick salivary cystatin
To successfully feed, ticks inject pharmacoactive molecules into the vertebrate host including cystatin cysteine protease inhibitors. However, the molecular and cellular events modulated by tick saliva remain largely unknown. Here, we describe and characterize a novel immunomodulatory cystatin, Iristatin, which is upregulated in the salivary glands of feeding Ixodes ricinus ticks. We present the crystal structure of Iristatin at 1.76 Å resolution. Purified recombinant Iristatin inhibited the proteolytic activity of cathepsins L and C and diminished IL-2, IL-4, IL-9, and IFN-γ production by different T-cell populations, IL-6 and IL-9 production by mast cells, and nitric oxide production by macrophages. Furthermore, Iristatin inhibited OVA antigen-induced CD4+ T-cell proliferation and leukocyte recruitment in vivo and in vitro. Our results indicate that Iristatin affects wide range of anti-tick immune responses in the vertebrate host and may be exploitable as an immunotherapeutic.
KeywordsCathepsin Crystal structure Immune responses Ixodes ricinus Saliva
We thank Professor Jose MC Ribeiro and Drs. Petr Kopáček and Daniel Sojka for constructive discussions, Dr. Daniel Sojka for kindly providing published reagent, ARVYS Proteins for service provision, Dr. Andrezza Campos-Chagas and Mr. Jan Erhart for technical assistance and Nextgenediting for editorial assistance. We also thank the anonymous reviewers for constructive comments about the draft.
JKot designed and performed experiments, performed the analyses, and wrote the manuscript; NS, MB, AC, ZB, PŘ, HL, and AS designed and performed experiments; JC and MK designed experiments, performed analyses, and edited the manuscript; MM and ES designed experiments and revised the manuscript; EC and JKop revised the manuscript.
This work was supported by the Grant Agency of the Czech Republic (Grant 19-07247S to MK and Grant 16-07117Y to JC), by the Grant Agency of the University of South Bohemia (Grant 038/2016/P to JKot), and by ERD Funds, project CePaViP OPVVV (No. CZ.02.1.01/0.0/0.0/16_019/0000759 to MK) and institutional project RVO 60077344 to MK. MB, MM, and PŘ were supported by project ChemBioDrug (No. CZ.02.1.01/0.0/0.0/16_019/0000729) from ERD Funds and institutional project RVO 61388963.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
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