Protective efficacy of antigens solubilized from gut membranes of the cattle tick, Boophilus microplus.

Triton X-100, SDS, n-octyl glucoside, and conditions of alkaline pH and high and low ionic strength, were used to solubilize membranes prepared from the mid-gut of the cattle tick Boophilus microplus. Hereford cattle (Bos taurus) were immunized with soluble membrane antigens in saponin, and then challenged twice with 20,000 tick larvae, 7 days apart. All soluble extracts, except that extracted with high ionic strength buffer, provided significant protection (56-78%) (P < 0.05) to immunized cattle compared with control cattle. Precipitation of the soluble n-octyl glucoside extract did not alter the immunogenicity of this vaccine. Where poor responses to membrane vaccines were obtained (< 60% protection), booster injections of antigen effected increased protection. The experimental cattle were typed for bovine major histocompatibility system class 1 antigens. The presence of three antigens (MB5, MB14 and MB20) had a significant effect on protective immunity induced by the membrane vaccines (P < 0.05). Protein profiles of Triton X-100, n-octyl glucoside and low ionic strength buffer extracts were compared by high-performance size-exclusion chromatography. Tick membranes extracted by either non-ionic detergents or low ionic strength solutions provided the best source of protective antigens.