Although primarily involved in proteinase inhibition,

the Kunitz domain has evolved to perform other functions requiring protein-protein interactions [32]. Cattle tick ovaries, fat body, hemocytes, and midgut contain Kunitz proteins find more [21], [29], [33] and [34]. Proteomic studies revealed the presence of Kunitz proteins that are up-regulated in ovarian tissue when R. microplus is infected with Babesia bovis [35]. A publicly available genomic database called CattleTickBase offers the opportunity to study the evolutionary history of Kunitz proteins in R. microplus [35]. It is possible that BmTI-6 and the RmLTI encoded by CK186726 are splice variants of the same gene or paralogs of the same Kunitz protein as suggested before for BmTI-A and other Kunitz proteins present in cattle tick ovary [34]. Previous GSK2118436 in vitro research documenting 72.8% efficacy against R. microplus infestation using purified trypsin inhibitors and the critical role Kunitz

proteins play in various biological processes including proteinase inhibition warrant continued vaccine discovery research with this protein family. Production of rRmLTI in P. pastoris facilitates its use to formulate polyvalent cattle tick vaccines that include other Kunitz proteins or different antigens from R. microplus. The level of immunoprotection attained through vaccination with rRmLTI was low as compared to other novel antigens discovered recently [37] and [43]. Of note are the results from vaccination using immunogenic peptides that yielded tick efficacy between 80 and 90% [44] and [45]. Salivary glands, midgut, and ovaries are prime targets to Ergoloid disrupt cattle tick

biology using vaccines and Kunitz proteins are abundant in those tissues. The use of epitopes from Kunitz proteins in combination with immunogenic portions of other tick molecules to produce a dual action vaccine could be another way to exploit the redundancy of R. microplus Kunitz inhibitors to innovate a highly efficacious cattle tick vaccine. Embrapa Beef Cattle, CNPq, and Fundect are gratefully acknowledged for financial support. This article reports the results of research only. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation of endorsement by the U.S. Department of Agriculture. F.D. Guerrero and A.A. Pérez de León are funded by USDA-ARS appropriated project 6205-32000-031-00D. The U.S. Department of Agriculture is an equal opportunity provider and employer.Conflict of statement: The authors declare that they have no competing interests. Authors contributions: RA developed proposal that was funded to test the immunoprotection of trypsin inhibitors from cattle tick larvae and helped prepare the article.