Cutaneous mast cell heterogeneity: response to antigen in atopic dogs

The role of mast cells in atopy: what can we learn from canine models? A thorough review of the biology of mast cells in canine and human systems

Mast cell research has largely focused on the role of these cells in the early phase of allergic reactions. However, their involvement may well extend beyond this stage, and even reach across nonallergic conditions. Mast cells from different sources have helped advance our knowledge of their biology. Although in vitro and in vivo research in this area has mainly focused on humans, such studies are limited by the extent to which cells from certain human tissues and/or human patients can be collected or studied. While rodents also provide valuable models with which to further our understanding of the behaviour of mast cells and their contribution to allergy, reported differences between human and murine mast cells, and, in some instances, the limitations of in vivo rodent models of mast cell-mediated allergic conditions, preclude their use. In this review, we introduce a relatively unknown mast cell population, that of the dog. Canine mast cells display many phenotypic and functional similarities with their human counterparts, and dogs develop spontaneous and induced allergic diseases that share clinical and pathophysiological features with the human condition. Therefore, the use of canine cells can shed light on the general role of mast cells, particularly in relation to allergic diseases given the potential of in vivo dog models within this field. Here we provide a detailed review of the data reported from in vitro and in vivo studies of canine mast cells, and compare them with results obtained in human systems. We also highlight direct evidence of the mast cell contribution to canine atopy. We conclude that the dog offers useful in vitro and in vivo models in which to investigate mast cell behaviour, and that its use should be considered when undertaking studies aimed either at elucidating the role of mast cells in health and disease, or at prescreening novel therapies prior to entry into man.

Changes in Morphology and Key Cytokine Gene Expression after Intradermal Injection of Louse (Bovicola ovis) Antigen in Sheep with Naturally Occurring Atopic Dermatitis

Groups of louse-infested and louse-naïve lambs (n=6 or 7) were used in two experiments to determine the sequential tissue response (macroscopical, microscopical and key cytokine mRNA) to intradermal injection of crude louse (Bovicola ovis) antigen over a period of 72 or 96 h. Histamine diphosphate and phosphate-buffered saline/glycerol (antigen vehicle control) solutions were also injected intradermally in each lamb for comparison. In both experiments, louse-infested lambs showed immediate and late-phase responses (LPRs) to louse antigen that differed significantly from the responses in the louse-naïve lambs. In experiment 1, biopsy samples taken at 7, 24, 48 and 96 h after injections showed more extensive dermal inflammation and leucocyte infiltration in response to louse antigen in louse-infested than in louse-naïve lambs. Eosinophils were significantly more numerous in the dermis of louse-infested lambs after all treatments and increased substantially in these lambs after antigen injection. Additionally, the louse-infested lambs differed from the naïve lambs in showing significantly higher mononuclear leucocyte and basophil infiltration and significantly lower neutrophil infiltration after antigen injection. In experiment 2, biopsy samples taken 4, 24, 48 and 72 h after injections showed trends in eosinophil infiltration of the dermis similar to those observed in experiment 1. Peak IL-4 mRNA expression was detected 4 h after antigen injection in the louse-infested lambs and remained significantly elevated at 24 h as compared with the results in the louse-naïve lambs. No significant difference in IFN-gamma mRNA expression between the louse-infested and the louse-naïve lambs was observed. These results indicated that louse-infested lambs show a cutaneous LPR analogous to that observed in atopic human beings and dogs. However, some differences were observed, including the longer duration of the LPR, the profuse eosinophil infiltration, and an absence of increased IFN-gamma mRNA expression.

Late-phase reactions to intradermal testing with Dermatophagoides farinae in healthy dogs and dogs with house dust mite-induced atopic dermatitis

OBJECTIVE

To determine the prevalence of late-phase reactions to intradermal testing with Dermatophagoides farinae in healthy dogs and dogs with atopic dermatitis and an immediate reaction to D farinae.

ANIMALS

6 healthy dogs and 20 dogs with atopic dermatitis and immediate reactions to D farinae.

PROCEDURE

ntradermal tests were performed with D farinae at 1:1,000 wt/vol and 1:50,000 wt/vol concentrations, and skin reactivity was evaluated after 0.25, 6, and 24 hours. Serum D farinae-specific IgE antibodies were assayed. Extent of lesions (atopy index) and pruritus (visual analogue scale) were evaluated in dogs with atopic dermatitis.

RESULTS

Late-phase reactions were observed in healthy dogs at 6 hours (n = 2 dogs) and 24 hours (1) with the 1:1,000 wt/vol concentration, and at 6 hours (1) and 24 hours (1) with the 1:50,000 wt/vol concentration of allergen. Late-phase reactions in healthy dogs were only observed in dogs with an immediate reaction to D farinae. Late-phase reactions were observed in 11 of 20 dogs with atopic dermatitis at 6 and 24 hours with the 1:1,000 wt/vol concentration and in 10 of 20 at 6 and 24 hours with the 1:50,000 wt/vol concentration of allergen. There was no difference in mean atopy index, mean visual analogue scale of pruritus, or mean serum D farinae-specific IgE concentration of dogs with a late-phase reaction, compared to dogs without a late-phase reaction.

CONCLUSIONS AND CLINICAL RELEVANCE

Late-phase reactions may be observed after an immediate reaction to intradermal skin testing in healthy and allergic dogs but are more commonly observed in dogs with atopic dermatitis.

The ACVD task force on canine atopic dermatitis (V): biology and role of inflammatory cells in cutaneous allergic reactions

Numerous inflammatory cells are thought to play a role in the pathogenesis of canine atopic dermatitis (AD) although, in the past, mast cells were considered the most important. However, evidence for this assumption is lacking. In this paper, we review the literature concerning the role of inflammatory cells in allergic reactions and conclude that a complex interplay exists between a wide variety of cell types. Thus, on the basis of the available evidence, the cells that appear to be the most important in the pathogenesis of canine AD are Langerhans' cells and dermal dendritic cells (both responsible for antigen processing and presentation), B-lymphocytes (responsible for reaginic antibody production), allergen-specific helper T-lymphocytes (responsible for cytokine production leading to activation of B-cells and other inflammatory cells) and mast cells (production of inflammatory mediators leading to inflammation).

The ACVD task force on canine atopic dermatitis (VI): IgE-induced immediate and late-phase reactions, two inflammatory sequences at sites of intradermal allergen injections

Intradermal testing is a common diagnostic procedure used in the evaluation of dogs with suspected atopic dermatitis (AD). To do this, most investigators assess the appearance of wheals that develop at the sites of intradermal allergen injections. However, wheals are rarely seen in dogs with naturally occurring AD. Furthermore, infiltration of inflammatory cells into the injection sites can occur 6-24h later, a phenomenon known as the late-phase reaction. The histological appearance of these late-phase reactions closely approximates that seen in the natural disease, suggesting that they might be more relevant than the immediate reactions. In this paper, we review the literature on immediate and late-phase reactions and re-assess the evidence for using current intradermal testing procedures as a diagnostic test in dogs.

Clinical and histological evaluation of an analogue of palmitoylethanolamide, PLR 120 (comicronized Palmidrol INN) in cats with eosinophilic granuloma and eosinophilic plaque: a pilot study

Fifteen cats with eosinophilic granuloma or eosinophilic plaque were given PLR 120 at the dosage of 10 mg kg-1 twice daily for one month. PLR-120 down-modulates mast cell degranulation via a receptor-mediated mechanism. No other drugs were permitted and cats were kept free of parasites throughout the study. A clinical evaluation and skin biopsies were performed before and after the treatment. Clinical improvement was assessed at 15 and 30 days. Mast cell numbers were counted and their granular content was assessed by densitometric analysis on toluidine blue-stained sections before and after the treatment. Ten of 15 (67%) cats showed clinical improvement of signs and lesions. There was no significant difference between mast cell numbers in skin biopsies taken before and after the trial, whereas the number of granules was significantly increased (P < 0.009). This pilot study suggests that PLR-120 might be a useful drug for the treatment of eosinophilic granuloma and eosinophilic plaque.

Skin mast cell releasability in dogs with atopic dermatitis

Isolated dermal mast cells from atopic dogs are a valuable tool for the analysis of their functional properties in atopic dermatitis. We have characterized the histamine secretory pattern of mast cells enzymatically dispersed from the skin of dogs naturally suffering from this condition. The total histamine content found per isolated skin mast cell was higher in the allergic dogs than in nonatopic (control) animals (8.7 pg/mast cell versus 5.2 pg/mast cell). This phenomenon together with the well known higher concentration of skin mast cell number in atopic dermatitis lesions might account for the observed increase in local histamine concentration (15.0 micrograms/g versus 9.0 micrograms/g). Atopic dog-derived mast cells were highly reactive to both non-immunological (ionophore A23187) and an immunological-like (concanavalin A) stimulus. Furthermore, histamine net release induced by concanavalin A (1 mg/ml) stimulation was clearly enhanced in the atopic dogs (33.3% net release versus 15.4% in controls). These results have not been described in dermal mast cells dispersed from the skin of individuals with atopic dermatitis and clearly support the hypothesis that mast cells play a major role in causing and possibly modulating atopic dermatitis, through enhanced sensitivity or releasability. However, whether these two phenomena are primary abnormalities of atopic dermatitis, or only secondary changes, remains undetermined.

Canine cutaneous mast cells dispersion and histamine secretory characterization

In view of the high incidence of canine cutaneous atopic disease and the relevance of mast cells to its pathogenesis, it was considered important to isolate firstly cutaneous mast cells from normal dog skin and to assess the histamine secretory activity, as this can be further used as a tool for the study of canine skin mast cell pharmacology in cutaneous atopy. The procedure for canine dermal mast cell dispersion following a skin enzymatic digestion (as for previous human skin mast cell dispersion methods) is described in detail. The number of canine cutaneous mast cells yielded per gram of skin was 2.31 +/- 0.21 x 10(5) representing 1.00% of the total cutaneous cells. The total histamine content per mast cell is 4.93 +/- 0.39 pg. Net histamine release owing to stimulation by calcium ionophore A23187 (1 microM) and concanavalin A (1 mg ml-1) was respectively 32.17 +/- 3.56% and 20.39 +/- 2.41% of the total amount per cell. Viability and reactivity to both stimuli of dispersed cutaneous mast cells were similar to the results found in humans. The present study allows further research on the role of mast cells immunopharmacology in allergy by investigation of cells isolated from canine skin in naturally occurring or experimentally induced atopy in the dog to be undertaken.

Mast cell chymase potentiates histamine-induced wheal formation in the skin of ragweed-allergic dogs

Skin mast cells release the neutral protease chymase along with histamine during degranulation. To test the hypothesis that chymase modulates histamine-induced plasma extravasation, we measured wheal formation following intradermal injection of purified mast cell chymase and histamine into the skin of ragweed-allergic dogs. We found that chymase greatly augments histamine-induced wheal formation. The magnitude of the potentiating effect increases with increasing doses of chymase and becomes maximal approximately 30 min after administration. Injection of chymase without histamine does not evoke wheal formation. The chymase potentiation of histamine-induced skin responses is prevented completely by pretreatment with the H1-receptor antagonist pyrilamine, and is prevented by inactivation of chymase with soybean trypsin inhibitor, suggesting that both histamine and preserved catalytic activity are required for the effects of chymase. To examine the effects of histamine and chymase released in situ in further experiments, we measured wheal size following local degranulation of mast cells by intradermal injection of ragweed antigen or compound 48/80. We found that pretreatment with either soybean trypsin inhibitor or pyrilamine markedly reduces ragweed antigen- or 48/80-induced wheal formation, supporting the results obtained by injection of exogenous chymase and histamine. These findings suggest a novel and important proinflammatory role for chymase in modulating the effects of histamine on vascular permeability during mast cell activation.

Inhibition of the cutaneous response to antigen by a thromboxane-synthetase inhibitor (OKY-046) in allergic dogs

We studied the effect of a selective thromboxane-synthetase inhibitor, sodium (E)-3-[4-(1-imidazolymethyl)-phenyl]-2-propanoate) (OKY-046) on the late-phase response to antigen in ragweed-sensitized dogs. Skin biopsies were performed before and 1, 6, and 24 hours after ragweed injection. OKY-046 was infused (100 micrograms.kg-1.min) from 1 hour before until 6 hours after intracutaneous ragweed in five dogs. The early clinical response to ragweed (wheal at 20 minutes) was not changed by OKY-046. A late-phase response (induration at 6 hours) was not observed in any of the OKY-046-treated dogs but was present at 6 hours in 4/5 dogs without OKY-046. Typical mast cells responded similarly in both groups with progressive degranulation during 24 hours. Maximal degranulation of atypical mast cells was delayed to 6 hours with OKY-046, whereas these cells responded completely at 1 hour without OKY-046. The inflammatory response to ragweed followed the same pattern in both groups, but the numbers of each cell type were decreased with OKY-046. With OKY-046, the cutaneous response to histamine was not changed significantly from baseline at 6 hours but was increased (p less than 0.05) at 24 hours, whereas without OKY-046, histamine response was significantly increased at 6 hours (p less than 0.001) and 24 hours (p less than 0.01). We conclude that OKY-046 alters the antigen-induced response of atypical mast cells, the subsequent cellular and clinical late-phase response, and prevents the increase in histamine response.

Effect of eicosapentaenoic acid in asthma

The role of arachidonic acid metabolites in the pathogenesis of airway inflammation and clinical asthma is currently unknown. The addition of eicosapentaenoic acid (EPA) to the diet of humans has been shown to generate metabolites that are less potent than their arachidonic acid counterparts. The substitution of EPA for arachidonic acid metabolites in patients might cause a decrease in airway inflammation and an improvement in clinical asthma. We studied the effect of addition of EPA to the diet of twelve asthmatic patients. Standard clinical evaluations and pulmonary function tests were done on weeks 0, 3, 6, 10, 12 and 14. Patients ingested either low-dose EPA (0.1 g/day) or high-dose EPA (4.0 g/day) from weeks 6-14 (total of 8 weeks). There was no difference in clinical status or pulmonary function between groups at the start of the study. There was no change in clinical status or pulmonary function between or within groups at the end of 8 weeks of EPA ingestion.