A cement protein of the tick Rhipicephalus appendiculatus, located in the secretory e cell granules of the type III salivary gland acini, induces strong antibody responses in cattle

Abstract

Protein components of the cement cone of ixodid ticks are candidates for inclusion in vaccines against tick infestation, since they are essential for tick attachment and feeding. We describe here the cloning of a cDNA encoding a 36 kDa protein, designated Rhipicephalus Immuno-dominant Molecule 36 (RIM36), present in salivary glands and the cement cone material secreted by Rhipicephalus appendiculatus. The 334-amino-acid sequence of RIM36 has a high content of glycine, serine and proline. The protein contains a predicted N-terminal signal peptide and two classes of glycine-rich amino acid repeats, a GL[G/Y/S/F/L] tripeptide and a GSPLSGF septapeptide. Comparison of genomic and cDNA sequences reveals a 597 bp intron within the 3' end of the RIM36 gene. Immuno-electron microscopy demonstrates that RIM36 is predominantly located in the e cell granules of the type III salivary gland acini. An Escherichia coli recombinant form of the proline-rich C-terminal domain of RIM36 reacts with antisera from Bos indicus cattle, either experimentally infested with R. appendiculatus, or exposed to ticks in the field. The 36 kDa protein is strongly recognised on Western blots of salivary gland lysates and soluble extracts of purified R. appendiculatus cement cones by polyclonal antibodies generated against recombinant RIM36, and by antisera from cattle experimentally infested with ticks. The data indicate that this tick cement component is a target of strong antibody responses in cattle exposed to feeding ticks.