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.
Highlights
Rhipicephalus (Boophilus) microplus tick infestations deeply affect cattle production because these parasites cause damage directly in addition to acting as vectors for disease-causing agents such as Anaplasma spp. and Babesia spp. [33]
We have previously shown that genes encoding for a glutamate-gated receptor and a glycine-like receptor are expressed at egg, larval and adult developmental stages of R. microplus [17, 18]
A prediction method of linear B-cell epitopes was applied on these sequences and results showed that the N-terminal extracellular domain (ECD) sequence of GluCl contained eight possible linear B-cell protective epitopes, whereas the N-terminal ECD sequence of glycine-like receptor (GlyR) exhibited eleven potential linear B-cell epitopes (Figs. 1C and 1F)
Summary
Rhipicephalus (Boophilus) microplus tick infestations deeply affect cattle production because these parasites cause damage directly in addition to acting as vectors for disease-causing agents such as Anaplasma spp. and Babesia spp. [33]. Chemical control remains the tick control method of choice [27] This practice regularly leads to the selection of tick populations resistant to the chemical used to treat infested cattle [16, 29, 32]. Immunological control has emerged as a promising alternative to restrain tick infestations and pathogen transmission. This new approach prompted the development and commercialization of vaccines based on the recombinant protein Bm86 [7, 21, 31, 36]. There is a need to characterize novel antigens in order to improve immunological protection
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