Americanum Larvae Research Articles

Rejection of ticks from guinea pigs by anti-hapten-antibody-mediated degranulation of basophils at cutaneous basophil hypersensitivity sites: role of mediators other than histamine.

Previous studies have established that recruitment of basophils to sites of tick feeding in guinea pigs is required to effect immune resistance. In the current study, actively sensitized guinea pigs treated three times daily with H-1 (mepyramine) and H-2 (cimetidine) histamine receptor antagonists, during the challenge tick infestation period, expressed normal resistance to Amblyomma americanum larvae. Similarly, naive guinea pigs treated with anti-histamines four times daily, beginning 7 days before transfer of immune serum and tick challenge and continuing through the tick infestation period, also expressed normal antibody-mediated resistance to A. americanum. These results indicated that histamine was not an important basophil mediator of the resistance response. Ticks allowed to feed on tissue rich in basophils that were induced by sensitization and subsequent local challenge with non-tick protein antigen, keyhole limpet hemocyanin (KLH), expressed normal yield. Ticks that fed on similar tissue rich in basophils induced by sensitization and challenge with KLH, in which the basophils expressed anti-picryl specificity due to systemic passive transfer of anti-picryl antibodies, were rejected when basophils were induced to degranulate by i.v. challenge with picryl antigen at 6 hr (29% rejection), 12 hr (18% rejection), 24 hr (22% rejection), and 48 hr (37% rejection) post-tick attachment. However, basophil degranulation at 18, 72 and 96 hr post-tick attachment had no adverse effect on tick feeding. These hosts were protected from systemic anaphylaxis by treatment with the anti-histamine mepyramine. Release of histamine occurred at tick feeding sites, but vasoactive effects were blocked by mepyramine treatment as evidenced by a lack of increased vascular permeability (bluing) at these sites compared with non-tick-infested tissues, or to cutaneous basophil hypersensitivity (CBH) sites of animals not protected with mepyramine. These results indicate that local recruitment and subsequent degranulation of basophils via immune mechanisms dependent on non-tick antigens can lead to tick rejection, and that basophil-derived mediators other than histamine are involved in this immune resistance response to A. americanum ticks. The identity of the crucial basophil mediator(s) is not known. The significant susceptibility of ticks to basophil-mediator release at 6 to 12 hr and 24 to 48 hr post-attachment coincides with the tick attaching and fast-feeding phases, respectively, suggesting that these phases of tick parasitism are particularly susceptible to the effect of basophil mediators other than histamine.

Blood eosinophil and basophil responses in guinea pigs parasitized by Amblyomma americanum ticks.

Guinea pigs sensitized to tick feeding by a previous infestation express immune resistance when challenged. This state is associated with large accumulations of eosinophils, and especially of basophils, at cutaneous sites of tick feeding. The present study shows that primary and secondary tick feeding stimulate blood eosinophilia and basophilia that reflect the infiltration of these cells in the skin. Primary feeding of Amblyomma americanum larvae resulted in a mean tick yield of 81%, mean tick weight of 0.91 mg and a feeding period of 3-5 days. Blood eosinophils and basophils began to rise on day 2 and reached peak 3-fold increases on day 4, the time of maximum tick drop-off. Secondary feedings 26 days later resulted in a mean tick yield of 45% (52% tick rejection), mean tick weight of 0.71 mg (22% weight decrease) and a mean feeding period of 4-6 days with maximum detachment on day 5. Prior to secondary tick feeding, both eosinophil and basophil levels were greater than in tick-free animals. Eosinophil levels peaked at day 4 to a level three times greater than in primary tick hosts. Basophil levels in secondary hosts exhibited minor elevations until day 6 when they were increased significantly, reaching a peak level of 33% higher than that observed in primary feedings. This study demonstrates that blood eosinophils and basophils respond quickly and significantly to primary tick feeding and undergo secondary responses of greater magnitude in response to subsequent tick challenge. However, challenge feeding resulted in a large blood eosinophilia with a modest blood basophilia. This may reflect the balance between bone marrow production and cutaneous accumulation of these cells at sites of tick rejection. Recruitment of eosinophils and basophils from the blood to the tissue site of tick feeding may contribute to the tick resistance mechanism.