Humoral immune responses of Hereford cattle vaccinated with midgut antigens of the cattle tick, Boophilus microplus

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Abstract
Summary Vaccination of cattle with midgut membrane (GM) antigen derived from the cattle tick, Boophilus microplus, injected with the adjuvant Quil A, resulted in significant increases in total immunoglobulins, mainly in the IgG1 and IgG2 fractions of the serum. Analysis of the anti‐GM antibody levels of vaccinated cattle showed that the levels of IgG, IgGl and complement‐fixing antibodies were significantly correlated to protection against infestation with cattle ticks. Anti‐GM antibodies of the IgG2 and IgM isotype were not correlated to protection against infestation with cattle ticks. Anti‐GM antibodies fixed complement (C′) in the presence of GM, larval membrane antigen and live, midgut cells, but not in the presence of live, larval cells. Anti‐GM antibodies were able to fix C′ equally well in the presence of GM antigen and live, midgut cells. None of the antigens tested activated the alternate pathway of complement under the conditions tested. Levels of anti‐GM IgG1 antibodies were used to develop a regression model for predicting levels of protection against infestation with cattle ticks in vaccinated cattle.