Esterase activity in the bovine sweat gland: genetic differences and the effect of temperature.

The esterase activity in the sweat glands of Brahman (B), Brahman crossbred (BX) and Shorthorn (S) steers was studied in animals exposed to low heat loads while grazing. The percentage of sweat glands containing esterase in the secretory cells of the fundus differed between genotypes and ranked in order of their heat tolerance, i.e., B greater than BX greater than S. Esterase activity in some of those secretory cells was reduced in B bulls by acute exposure to high air temperatures in a climate chamber. While the significance of the esterase-containing cells in the fundus of the bovine sweat gland is uncertain, the results suggest that they could represent the resting or relatively inactive stage of the secretory cells.

Comparison of cutaneous hyperemia in cattle elicited by larvae of Boophilus microplus and by prostaglandins and other mediators.

Blood flow has been measured in bovine skin following the injection of tick antigens and a number of pharmacological mediators; including histamine, prostaglandins and slow reacting substance of anaphylaxis. The greatest increase in blood flow (20 times normal) was recorded with tick antigens and with prostaglandin F2. This mediator may therefore influence blood flow during immune reactions to ticks and during the rapid ingestion of blood by the ticks.

Arteriovenous anastomoses in the dermal vasculature of the skin of Bos taurus cattle, and their relationship with resistance to the tick, Boophilus microplus.

Bos taurus cattle with high resistance to the tick Boophilus microplus, whether free-grazing or in covered pens, had significantly more arteriovenous anastomoses (AVA) in their skin than did animals of low resistance. These differences in number of AVA associated with resistance level were most marked above the level of the sebaceous gland in the neck region, an area favoured for tick feeding. In this skin layer, the number of AVA in low-resistance animals (4.0 plus or minus 0.4 per 2.1 mm) was significantly lower than in animals of high resistance (12.3 plus or minus 2.2 per 2.1 mm) while the mean value for the naive animals (8.2 plus or minus 1.0 per 2.1 mm) was intermediate. No differences in morphology of AVA were detectable between the three groups using light microscopy.

Cutaneous hyperaemia elicited by larvae of the cattle tick, Boophilus microplus.

The responses of skin capillary blood flow (BF) to infestation by larvae of B. microplus have been determined using radioactive microspheres. Larvae were placed in gauze-covered rings glued to the closely clipped skin. In pilot experiments on three Brahman-cross calves which had prior exposure to ticks, BF measurements at intervals up to 25 h post-infestation revealed a continuing increase. 'High' rates of infestation (5000 larvae per ring) elicited up to an 80-fold increase in BF. In four Australian Illawarra Shorthorn (AIS) calves with prior exposure to ticks, BF had increased by 0.5 h post-infestation, it reached a peak at 24 h, and fell markedly by 48 and 75 h. In contrast, two AIS calves without prior tick exposure showed no significant increase in BF until 24 h and this increase continued until observations were terminated at 72 h. BF in the neck area (normally favoured by ticks) increased most in calves of highest resistance to ticks, but the flank area (normally unfavoured) showed no consistent difference in BF response between animals of different tick resistance. It is concluded that skin capillary hyperaemia is triggered by the host's immune response to larval attachment. Within the relatively narrow range of tick resistance in the present animals, the degree of hyperaemia was directly related to level of resistance to the tick in skin regions normally favoured by ticks and therefore it may play a role in determining resistance to ticks.

A putative role for eosinophils in tick rejection.

In the reaction of Bos taurus cattle to infestation by the tick Boophilus microplus, mast cell histamine is translocated by the eosinophils to the attachment site. The concentration pattern of this cutaneous mediator for pain appears related to the grooming behaviour of the host.

Boophilus microplus: cellular responses to larval attachment and their relationship to host resistance.

The histology of early feeding lesions of the cattle tick B. microplus has been studied using 32P labelled larvae to standardize the duration of attachment. Critical studies were made on 3-h lesions in six separate experiments on different groups of British breed animals. Each group consisted of three animals--one previously unexposed to ticks, one of high resistance and one of low resistance. The degree of mast cell disruption, eosinophil concentration and degranulation, and the extent of epidermal vesiculation were all significantly greater at the site of attachment on highly resistant hosts. In previously unexposed animals there was no mobilization of eosinophils nor mast cell breakdown and no epidermal vesiculation. Possible immune mechanisms producing mast cell disruption and the infiltration and concentration of eosinophils are suggested, and the effect of eosinophil degranulation on larval attachment and feeding is discussed.

Boophilus microplus: characterization of enzymes introduced into the host.

A number of enzymes, presumably secreted by larvae of B. microplus under natural feeding conditions, have been investigated in the skin of previously unexposed calves 4 h after infestation at the attachment site. Carboxylic ester hydrolase activity was demonstrated in the dermis, immediately adjacent to the mouthparts, or in the attachment cone, depending on substrate and reaction pH. The carboxylic ester hydrolase acting on naphthol AS-D acetate (2-acetoxy-3-naphthoic-O-toluidide) at pH 7-1 was characteristically found in the dermis and not in the attachment cone. The use of specific inhibitors showed that this enzyme was primarily a B-esterase or carboxylesterase with possibly a small portion of C-esterase or acetylesterase. It is postulated that carboxylic ester hydrolase could contribute to the dilation observed in the subepidermal capillaries adjacent to the attachment sites of unexposed animals, through the formation of plasma kinins. Other enzymes demonstrated in the dermis, adjacent to the mouthparts, were triacylglycerol lipase, as an aggregated deposit, and small amounts of aminopeptidase (microsomal) and monophenol monooxygenase. Aminopeptidase (microsomal) was also demonstrated in the attachment cone or adjacent epidermis, according to the substrate used. No activity was found in the host tissue, in association with the attachment site, for either alkaline or acid phosphatase, acetylcholinesterase or cholinesterase, peroxidase or amine oxidase (flavin-containing), despite the intense histochemical reaction for the latter in the tissues of larvae.