Immunization of rabbits with Amblyomma hebraeum nymphal homogenates and implications for the host amplification system.

Immunochemical mechanisms involved in tick rejection by a host are not well documented. The role of serum globulins, and that played by the amplification system's humoral products (thrombin from the coagulation, plasmin from the fibrinolytic, and kallikrein from the kinin systems) in tick-resistant animal hosts have not yet been demonstrated. It is known, however, that factors C1, C3 and C5 of the complement system play a role in tick rejection, and that factors C3a and C5a are anaphylatoxins capable of degranulating leukocytes, thereby releasing pharmacologically active vasoamines which are involved in tick rejection. In this study, levels of kininogen increased by 56% and those of fibrinogen by 19% in rabbits immunized with nymphal antigens. A highly significant (P < 0.001) number of nymphs that fed on the immunized rabbits failed to moult into adult stages. It is reported for the first time, that increased levels of two glycoproteins, fibrinogen and kininogen occurred in rabbits immunized with homogenates of Amblyomma hebraeum ticks. The role played by the amplification system in tick rejection in resistant animals is clarified.

Acquisition of protective immunity in Geochelone pardalis against Amblyomma marmoreum (Acari:Ixodidae) nymphal ticks.

Significant increases in serum globulins (alpha 1, alpha 2, beta and gamma) were observed in mountain leopard tortoises (Geochelone pardalis) after they had been immunized with nymphal homogenates of Amblyomma marmoreum. There was a concomitant significant increase in the numbers of leukocytes (lymphocytes, basophils, monocytes and eosinophils). Resistance to nymphal-challenge infestations was manifested by reduced feeding time, lower engorgement masses, and significantly fewer (P < 0.0001) numbers of nymphs that moulted. These findings are contrary to the generally reported phenomenon, that ticks do not induce resistance in their natural hosts.

Immunization of rabbits against nymphs of Amblyomma hebraeum and A. marmoreum (Acari: Ixodidae).

Himalayan rabbits immunized with homogenates prepared from nymphs of Amblyomma hebraeum Koch and A. marmoreum Koch ticks developed humoral and probably also cell-mediated immunity to their respective homogenates. Beta and gamma globulin levels and numbers of eosinophils and neutrophils increased significantly in inoculated rabbits. The recipient animals developed resistance to homospecific nymphal infestations. Cross resistance between the two species was not evaluated. Nymphs of both species that fed on inoculated rabbits demonstrated slightly shorter feeding periods, and their mean weights were significantly lower than nymphs that fed on Quil 'A' adjuvant-inoculated rabbits or on naive rabbits. Significantly higher proportions of nymphs from immunized animals failed to moult when compared with nymphs that fed on the two control groups. These parameters indicate that the inoculated rabbits had acquired protective immunity against nymphs of both ticks.

Immunization of guinea-pigs and cattle against adult Rhipicephalus appendiculatus ticks using semipurified nymphal homogenates and adult gut homogenate.

Guinea-pigs inoculated with crude homogenate of unfed nymphs of the tick Rhipicephalus appendiculatus and with three semipurified fractions of the homogenate obtained by gel permeation chromatography, acquired a significant degree of immunity to infestation with adults of this tick. Fraction 2 induced the highest reduction (66%) in mean weight of engorged females followed by crude homogenate and fractions 1 and 3. Calves immunized with crude homogenates of unfed nymphs, fraction 2 of nymphal homogenate, and gut homogenate of unfed females also acquired immunity against adults of R. appendiculatus. The mean weight of engorged females fed on calves inoculated with nymphal fraction 2 was the lowest of all five groups of calves on which females fed. The reduction in weight (38%) was not significantly different from that observed for females fed on calves inoculated with crude nymphal homogenate (31%) or females from third infestation of adult ticks. No differences in the weight and hatchability of egg batches produced by engorged females collected from the five groups of calves were observed. Analysis of sera collected from the five groups of calves showed that the concentration of albumin, alpha-1, alpha-2 and beta-globulins fluctuated and no significant differences between the treated groups were observed. The levels of gamma-globulin increased in treated groups including the group inoculated with adjuvant only, but unlike previous reports no increase in gamma-globulin or a correlation between the level of gamma-globulin and the degree of resistance acquired were observed in calves exposed to repeated tick infestations. However, the increase in the concentration of gamma-globulin in calves inoculated with fraction 2 or crude nymphal homogenate was higher than that observed in the other groups.