Kinetics of mast cell, basophil and eosinophil populations at Hyalomma anatolicum anatolicum feeding sites on cattle and the acquisition of resistance.

The cutaneous cellular reactions associated with acquisition of resistance by cattle to Hyalomma anatolicum anatolicum feeding were investigated by comparing the nature and sequence of cellular events at H.a. anatolicum feeding sites following primary and tertiary infestations. Cattle acquired resistance to H.a. anatolicum feedings after a single infestation. The resistance was manifested by a significant reduction in the mean weight of engorged females and mean weight of egg mass produced, failure to lay eggs and sometimes death of ticks in situ. The acquisition of resistance corresponded with pronounced epidermal vesiculation and a significant change in the nature of the cellular infiltrate at tick feeding sites indicating the development of cutaneous hypersensitivity. On primary infestation the cellular infiltrate was dominated by neutrophils (43-71%) followed by mononuclear cells (25-35%). Basophil and eosinophil infiltration in small numbers was noticed for the first time at 72 and 144 h, respectively, post-primary infestation. Unlike primary infestation, the dermal infiltrate on tertiary infestation, 24 h after attachment, was characterized by infiltration of basophils (6%) and eosinophils (3%) and a marked degranulation of mast cells and basophils. Basophils showed a consistent increase in absolute as well as relative numbers as the feeding advanced. They were the second most abundant cell types after neutrophils (48-68%) at 72 h (16%), and 144 h (23%). Eosinophils (3-9%) and mononuclear cells also showed a significant increase in their mean numbers as compared with primary infestation. There was a progressive decrease in the number of detectable mast cells following tick infestation and they were significantly lower post-tertiary infestation, compared to primary infestation. These results suggest that the pharmacological mediators released by degranulation of mast cells and basophils are perhaps the major effectors of resistance in cattle to H.a. anatolicum.