Investigations into lymphocyte transformation and histamine release by basophils in sheep repeatedly infested with Rhipicephalus evertsi evertsi ticks.

The immune response of a natural host of Rhipicephalus evertsi evertsi to feeding by this tick species was investigated with respect to the effects of tick salivary gland extracts on the transformation of peripheral blood lymphocytes and the release of histamine by basophils obtained from repeatedly infested sheep. The results indicated that there was no stimulation of lymphocyte transformation but that histamine release was elevated 10 fold after four infestations. Although this suggests a hypersensitivity reaction, believed to be a major factor in resistance to tick feeding, it was observed that ticks fed normally even after four infestations with 28 day intervals in between. These results emphasize the adaptation of ticks to feeding on their natural hosts.