Tick feeding and the development of immunity to Hyalomma anatolicum anatolicum

A study on the role of the salivary glands of Hyalomma anatolicum anatoIleum in feeding, acquisition of host resistance and the cutaneous reactions to tick feeding has been made. To investigate the sequential structural changes occurring in the salivary glands during feeding and the nature of potential secretory products, light and electron microscopy studies were coupled with histochemical tests on salivary glands and tick feeding sites. The salivary glands of H.a. anatolicum consisted of three types of acinus (I, II and III) in females and an additional type IV acinus in males. The ultrastructural features of the peripheral cells of the type I acinus supported the hypothesis that these acini secrete concentrated salts during questing stages of the life cycle to absorb water from unsaturated air. There were five granular cell types (a, b, c₁-c₃) in the type II acinus, three (d, e, f) in the type III acinus and one (g) in the type IV acinus. The attachment cement of H. a. anatolicum was lipoprotein in nature and appeared to have been derived from the a cells of type II, and d and e cells of type III acini, the secretory granules of which had similar histochemical properties. A strong aminopeptidase and moderate acid phosphatase activity was also found localized in the attachment cement. In addition,deposits of glycoprotein and non-specific esterase materials, probably derived from the b and/or c cells of type II acini were located in the feeding lesion. The interstitial cells which were insignificant in unfed ticks became more distinct during feeding. In females the interstitial cells of type III acini enlarged markedly to form a basolateral labyrinth with the transformed f cells forming a water excretory unit during the rapid phase of engorgement. Saliva and salivary gland extracts from 96 hour fed female ticks were fractionated by SDS-PAGE, immunoblotted and developed by autoradiography and enzyme labelled antibody to identify salivary protein involved in the induction of resistance to tick feedings. Sera from hypersensitized rabbits recognised nine antigenic proteins in the saliva and 17 in the salivary gland extracts. Antigenic proteins ranged in molecular weight from 14,400 to 130,000 daltons. All the antigens thus identified were glycoproteins. In addition,antigen I (molecular weight 130,000 daltons) showed acid phosphatase, and antigen III (molecular weight 96,000 daltons) both non-specific esterase and aminopeptidase activity. Intradermal inoculation of antigens I, II, III, saliva and salivary gland extracts into tick-exposed rabbits elicited immediate and delayed hypersensitivity reactions. Detailed sequential quantitative histological analysis of tick feeding sites following primary and tertiary feedings was made to gain an insight into cellular interactions inimical to ticks. On primary infestation the cellular infiltrate at H. a., anatolicum feeding sites in rabbits and cattle was dominated by neutrophils followed by mononuclear cells. The infiltration of eosinophils and basophils at tick feeding sites was an early event in rabbits (24 hours) as compared to cattle (144 hours). On tertiary infestation the tick feeding sites in both rabbits and cattle were characterized by massive degranulation of mast-cells and basophils. Comparing the nature and magnitude of cellular infiltrate at tick feeding sites in rabbits and cattle, basophils appeared to be the major effectors of resistance in this system. The stronger expression of resistance in cattle corresponded with a high level of cutaneous basophil response (6-23%) as compared to rabbits (3-9%). The possible mechanisms by which the mediators released by degranulating cells mediate resistance are suggested and discussed