Immunoglobulin-E-bearing cells in skin biopsies of horses with insect bitehypersensitivity

The aim of the present study was to investigate, with immunohistochemistry and in situ hybridisation, if immunoglobulin-E (IgE) and mast cells are inv olved in the pathogenesis of insect bite hypersensitivity (IBH), an allergi c dermatitis of horses. In tissue sections fixed in paraformaldehyde (PFA) for < 24 h, significantly more IgE protein-bearing cells were found in the dermis and epidermis of acute and chronic IBH lesions than in skin biopsies from healthy horses (medians = 466, 236 and 110 CellS/mm(2), respectively; P less than or equal to 0.01). More IgE-mRNA positive (+) cells were obser ved in the dermis of acute IBH lesions than in the dermis of healthy skin ( median = 2.8 vs. 0.0 cellS/mm(2); P less than or equal to 0.01). Significan tly, more mast cells were detected with metachromatic (median = 160 vs. 62 cells/mm(2); P less than or equal to 0.001) and tryptase-specific stainings (median = 120 vs. 69 cells/mm(2); P less than or equal to 0.001) in the de rmis of acute IBH biopsies compared to healthy skin. No chymase+ mast cells were found in any skin biopsy. IBH lesions fixed in PFA for > 24 h were co mpared to dermatomycosis (DM) lesions; IBH biopsies contained a similar num ber of IgE-protein+ cells to DM biopsies (median = 249 vs. 192 cells/mm(2); P = 0.08) but had significantly more IgE-mRNA+, metachromatic and tryptase + mast cells than DM biopsies. This study suggests an involvement of IgE-me diated immune reactions in the pathogenesis of IBH as well as, sometimes, i n dermatomycosis. Using double labelling, cells which expressed IgE protein and contained mast cell enzymes were detected.