Sequence variations in the Boophilus microplus Bm86 locus and implicationsfor immunoprotection in cattle vaccinated with this antigen

Cattle tick infestations constitute a major problem for the cattle industry in tropical and subtropical regions of the world. Traditional control meth ods have been only partially successful, hampered by the selection of chemi cal-resistant tick populations. The Boophilus microplus Bm86 protein was is olated from tick gut epithelial cells and shown to induce a protective resp onse against tick infestations in vaccinated cattle. Vaccine preparations i ncluding the recombinant Bm86 are used to control cattle tick infestations in the field as an alternative measure to reduce the losses produced by thi s ectoparasite. The principle for the immunological control of tick infesta tions relies on a polyclonal antibody response against the target antigen a nd, therefore, should be difficult to select for tick-resistant populations . However, sequence variations in the Bm86 locus, among other factors, coul d affect the effectiveness of Bm86-containing vaccines. In the present stud y we have addressed this issue, employing data obtained with B. microplus s trains from Australia, Mexico, Cuba, Argentina and Venezuela. The results s howed a tendency in the inverse correlation between the efficacy of the vac cination with Bm86 and the sequence variations in the Bm86 locus (R-2 = 0.7 ). The mutation fixation index in the Bm86 locus was calculated and shown t o be between 0.02 and 0.1 amino acids per year. Possible implications of th ese findings for the immunoprotection of cattle against tick infestations e mploying the Bm86 antigen are discussed.