A salivary histamine-binding protein from Rhipicephalus microplus and its evaluation as an anti-tick vaccine antigen.

The cattle tick Rhipicephalus microplus is an ectoparasite of major economic importance to livestock, particularly in tropical and subtropical regions. The lack of effective vaccines against tick infestation has hindered its control and the identification of new molecular targets for recombinant vaccine development arises as an alternative strategy. Tick saliva is known as a reservoir of potential vaccine targets, including several proteins involved in attachment, immune response modulation and feeding that targeting might affect tick infestations. Among these proteins, histamine binding proteins (HBPs) sequester host histamine molecules reducing itching and pain response, allowing that ticks attach to the host and get a complete blood meal. In this study, we aimed to functionally and immunologically characterize a putative HBP from R. microplus (BrRm-HBP) and evaluate its potential as an anti-tick vaccine. In silico analyses indicated that BrRm-HBP is conserved among tick species and presents structural features consistent with known tick HBPs. Immunohistochemical assays demonstrated its localization in salivary glands, supporting its potential role at the tick-host interface. Recombinant BrRm-HBP was expressed in Escherichia coli and showed histamine-binding activity. Immunization of rabbits with recombinant BrRm-HBP elicited a humoral immune response. Moreover, vaccination conferred partial protection in rabbits experimentally infested with the closely related tick Rhipicephalus linnaei. These findings indicate that BrRm-HBP is a functional and immunogenic salivary protein potentially involved in tick-host interactions and may represent a promising candidate for new anti-tick vaccine formulations.