Lesser protein degradation machinery correlates with higher BM86 tick vaccine efficacy in Rhipicephalus annulatus when compared to Rhipicephalus microplus.

Infestations with cattle ticks, Rhipicephalus (Boophilus) microplus and Rhipicephalus annulatus, economically impact cattle production in tropical and subtropical regions of the world. Vaccines containing the recombinant R. microplus BM86 gut antigen were developed and commercialized to induce an immunological protection in cattle against tick infestations. These vaccines demonstrated that tick control by vaccination is cost-effective, reduces environmental contamination and prevents the selection of drug resistant ticks that result from repeated acaricide applications. The protection elicited by BM86-containing vaccines against tick infestations is mediated by a collaborative action between the complement system and IgG antibodies. The efficacy of the vaccination with BM86 and other tick antigens is always higher for R. annulatus than against R. microplus, suggesting that tick genetic and/or physiological factors may affect tick vaccine efficacy. These factors may be related to BM86 protein levels or tick physiological processes such as feeding and protein degradation that could result in more efficient antibody-antigen interactions and vaccine efficacy. To test this hypothesis, we compared the proteome in R. annulatus and R. microplus female ticks after feeding on BM86-vaccinated and control cattle. The results showed that cattle proteins were under represented in R. annulatus when compared to R. microplus, suggesting that R. annulatus ticks ingested less blood, a difference that increased when feeding on vaccinated cattle, probably reflecting the effect of antibody-BM86 interactions on this process. The results also showed that tick protein degradation machinery was under represented in R. annulatus when compared to R. microplus. BM86 mRNA and protein levels were similar in both tick species, suggesting that lesser protease activity in R. annulatus results in more efficient antibody-antigen interactions and higher vaccine efficacy. These results have important implications for tick vaccine research, indicating that not only genetic differences, but also physiological factors may influence tick vaccine efficacy.