Immunoprotection evaluation of the recombinant N-terminal domain of Cys-loop receptors against Rhipicephalus (Boophilus) microplus tick infestation

Abstract

Rhipicephalus (Boophilus) microplus ticks are obligatory hematophagous ectoparasites of cattle and act as vectors for disease-causing microorganisms. Conventional tick control is based on the application of chemical acaricides; however, their uncontrolled use has increased resistant tick populations, as well as food and environmental contamination. Alternative immunological tick control has shown to be partially effective. Therefore, there is a need to characterize novel antigens in order to improve immunological protection. The aim of this work was to evaluate Cys-loop receptors as vaccine candidates. N-terminal domains of a glutamate receptor and of a glycine-like receptor were recombinantly produced in Escherichia coli. Groups of BALB/c mice were independently immunized with four doses of each recombinant protein emulsified with Freund’s adjuvant. Both vaccine candidates were immunogenic in mice as demonstrated by western blot analysis. Next, recombinant proteins were independently formulated with the adjuvant Montanide ISA 50 V2 and evaluated in cattle infested with Rhipicephalus microplus tick larvae. Groups of three European crossbred calves were immunized with three doses of each adjuvanted protein. ELISA test was used to evaluate the IgG immune response elicited against the recombinant proteins. Results showed that vaccine candidates generated a moderate humoral response on vaccinated cattle. Vaccination significantly affected the number of engorged adult female ticks, having no significant effects on tick weight, egg weight and egg fertility values. Vaccine efficacies of 33% and 25% were calculated for the glutamate receptor and the glycine-like receptor, respectively.

Tick Vaccines and Concealed versus Exposed Antigens

“…This is not because it presents a ground-breaking discovery, but rather because it is a robust collection of evidence supporting the different research paths being followed in the pursuit of effective tick and tick-borne pathogens vaccines. Since then, at least 68 different “exposed” and/or “concealed” antigens have been tested in vaccination trials against different tick species aiming to achieve a reduction in tick infestation ( Table 1 ) [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ]. The attractive idea of transmission blocking vaccines has also thrived, and some studies have included the hypothesis that impairing a tick targeted antigen could also affect the pathogen life cycle occurring within its vector ( Table 1 ).…”

“…Even though there is a growing awareness of the necessity to create models to analyze the existing data, unfortunately, these resources, which can be perceived as the first step on the road towards the discovery of suitable targets, tend to be underexplored. Reverse vaccinology, pioneered by Rino Rappuoli [ 61 ] has also been applied in anti-tick vaccine development, with the development of bioinformatic pipelines designed to identify suitable targets [ 54 , 62 , 63 ].…”