Cloning and characterization of Rhipicephalus appendiculatus voraxinalpha and its effect as anti-tick vaccine.

Male tick-derived voraxinalpha and voraxinbeta, a pair of testicular proteins, are transferred to female via copulation to stimulate female blood feeding in the tick Amblyomma hebraeum (A. hebraeum). Immunized animals with recombinant (r-)voraxinalpha and voraxinbeta have been shown as highly resistant to the tick infestation. In this study, we describe the cloning and characterization of voraxinalpha homologue from the tick Rhipicephalus appendiculatus (R. appendiculatus), the major vector for East Coast fever in Eastern Africa. The sequence analysis of the R. appendiculatus voraxinalpha indicated that the deduced amino acid sequence had high similarity with voraxinalpha of the tick A. hebraeum and Dermacentor variabilis, suggesting that voraxinalpha is conserved in different tick genera. Quantitative RT-PCR and Western blotting analysis showed that male voraxinalpha was predominantly expressed in testis and its expression was induced by blood feeding. R. appendiculatus voraxinalpha was not secreted into the host during tick feeding and was detected in mated female hemolymph as measured by Western blotting. Preliminary vaccination of rabbits with r-voraxinalpha elicited the humoral immunity and conferred protective immunity against female ticks, resulting in the reduced fed weight. These results suggest that r-voraxinalpha could be a good candidate as anti-tick vaccine.