Differential cellular responses at Hyalomma anatolicum anatolicum feeding sites on susceptible and tick-resistant rabbits.

The sequential, quantitative histological analysis of adult Hyalomma anatolicum anatolicum feeding sites on rabbits showed that the cellular reactions at tick feeding sites change in character and magnitude with time after attachment, and differ considerably from primary infestation to tertiary infestation. Neutrophils (62-68%) followed by mononuclear cells (22-24%) were the major component of the cellular infiltrate throughout primary infestation. Eosinophils accounted for 10% of the cellular infiltrate at 24 h after attachment. Their proportions declined thereafter, forming 9% of the infiltrate at 72 h and 5% at 144 h. Basophil infiltration in most of the feeding lesions was noticed by 24 h, but always in low numbers. Despite a slight increase in absolute numbers the proportion of basophils fell from 3% at 24 h to 2% at 144 h. In contrast to primary infestation the cellular reactions on tertiary infestations were characterized by a significant increase in the numbers of basophils and eosinophils and marked degranulation of mast cells and basophils as early as 24 h after attachment. As the feeding advanced there was an increase in the mean proportions of basophils from 4% to 9% and mononuclear cells from 22% to 38%, and a decrease in the proportion of eosinophils from 21% to 9%. However, neutrophils (42-53%) remained the major component of the cellular infiltrate. There was no significant difference in the nature and sequence of cellular events in the feeding sites of male and female ticks, although the lesions produced by feeding males were 5-10 fold smaller than those of females. Mast cells, basophils and eosinophils appeared to be the major host cells involved in the resistance response, manifested by protracted feeding, reduced engorgement weight and poor egg laying. The mechanisms by which these cells might interact to mediate resistance are suggested and discussed.