The effect of antigen concentration and vaccine regimen on the immunity induced by membrane antigens from the midgut of Boophilus microplus.

Sheep and cattle were immunized with membrane antigens extracted from the midgut (GM) of the cattle tick Boophilus microplus, and antibody levels were measured by enzyme-linked immunosorbent assay (ELISA). One microgram of GM induced an antibody response in sheep comparable to that induced by 500 micrograms GM. Single or divided doses of 500 micrograms GM induced the same antibody levels in sheep over 12 weeks. Cattle vaccinated with either 500 micrograms GM in two doses or with 50 or 500 micrograms GM in three doses had significant antibody responses (P less than 0.05) and were equally protected (89%, 80% and 95%, respectively, calculated from tick egg weights) against challenge with 40,000 ticks, compared to control cattle. In another experiment, cattle vaccinated with 2.95 mg GM divided into 12 doses over 6 months had antibody levels that reached a plateau after 1.2 mg GM were administered, and were significantly protected (96%) against challenge.