Immunoglobulin E‐bearing cells and mast cells in skin biopsies of horses with urticaria

Abstract

The pathogenesis of equine urticaria is not well understood. In man, urticaria has been associated with immunological and nonimmunological mechanisms leading to the release of various mediators by mast cells. Skin biopsies of 32 horses with a history of urticaria were stained with toluidine blue, a double-labelling method for chymase and tryptase, and immunohistochemistry for immunoglobulin (Ig)E. These horses were compared with horses with pemphigus foliaceus, insect bite hypersensitivity and control horses with healthy skin. Neither formalin fixation time nor biopsy site influenced the staining methods. No chymase-positive cells were found. In all groups of horses, cells staining with toluidine blue and for tryptase and IgE were found in the epidermis and hair follicle papilla and significantly more positively staining cells were observed in the subepidermal dermis compared with the deep dermis. Horses with urticaria had significantly more IgE-bearing cells in the subepidermal dermis than control horses. However, horses with urticaria had significantly fewer toluidine-blue-stained mast cells in both subepidermal and deep dermis compared with the insect bite hypersensitivity and pemphigus foliaceus groups. This study suggests that IgE-mediated reactions play a role in the pathogenesis of urticaria.

Skin Immune System and Allergic Skin Diseases

“…3,[26][27][28][29] Some authors have suggested that such training/racing-associated urticarias may represent an interplay of stress and supplemented diets. { No age, breed, or sex predilections have been proven for urticaria and angioedema in horses.…”

Characterization of IgE-mediated cutaneous immediate and late-phase reactions in nonallergic horses

“…1,20,22,[31][32][33] In the present study, more eosinophils were found in the deep layer of dermis in anti-IgE injected skin. Investigators of a previous study 9 conducted to evaluate effects of ID injection of anti-IgE in dogs described cellular counts only in the most superficial dermis.…”

“…This degranulation phenomenon has been reported previously in humans 30 and has been postulated to occur in horses. 22 Investigators in 1 study 20 examined mast cells in the skin of horses with IBH by use of toluidine blue stain and immunohistochemical analysis for chymase and tryptase. The effect of fixation time was also evaluated.…”

“…8,17,18 Atopic dermatitis 1 and IBH 1,19 in horses involve type I hypersensitivity reactions. The involvement of IgE, specifically, has been suggested 7,20 and established 21,22 in allergic skin disease of horses. Horses affected by IBH have increased expression of both IgE protein and mRNA in dermal cells of affected skin, compared with results for unaffected skin of clinically normal horses, especially in the acute phase.…”

“…20 Examination of skin biopsy specimens obtained from horses with urticaria also revealed that there were more IgE-bearing cells in the superficial dermis, compared with the number of those cells in skin biopsy specimens obtained from clinically normal horses. 22 Type I hypersensitivity reactions can be simulated by ID injection of anti-IgE antibodies, 23 which functions to cross-link surface IgE and mimic the effects of an allergen. This reaction has been used in humans to evaluate the effects of drugs on IgE-mediated reactions.…”