The effect of various adjuvants on the humoral immune response of sheep and cattle to soluble and membrane midgut antigens of Boophilus microplus.

Sheep and cattle were immunized with soluble and membrane midgut antigens of the cattle tick, Boophilus microplus in association with various adjuvants, and antibody levels to soluble and membrane midgut extracts were measured by enzyme-linked immunosorbent assay (ELISA). The adjuvants used were Quil A, Freund's incomplete adjuvant (FIA) and aluminium hydroxide (A1(OH)3). Significant antibody levels to midgut membrane antigen (GM) were not detected in the sera of sheep immunized with GM plus A1(OH)3. However, membrane and soluble midgut antigens combined with Quil A generated significantly higher levels of antibodies in sheep than these antigens emulsified in FIA (P < 0.05). In cattle, although soluble midgut antigen (GS) plus Quil A induced significantly higher levels of antibodies compared with GS in FIA (P < 0.05), neither preparation provided significant protective immunity against challenge with B. microplus (46% and 22%, respectively). A soluble form of membrane midgut antigen extracted by low ionic strength buffer (LI-GM) when combined with Quil A provided 83% and 87% protection against challenge with B. microplus in two separate experiments. Quil A was clearly superior to FIA and A1(OH)3 as an adjuvant for these tick antigens.