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