IgE-bearing cells in bronchoalveolar lavage fluid and allergen-specific IgE levels in sera from RAO-affected horses.

Recurrent airway obstruction (RAO) is a common condition in stabled horses characterized by small airway inflammation, airway neutrophilia and obstruction following exposure of susceptible horses to mouldy hay and straw and is thus regarded as a hypersensitivity reaction to mould spores. However, the role of immunoglobulin E antibodies (IgE) in the pathogenesis of RAO is unclear. We hypothesized that the number of cells with receptor-bound IgE in bronchoalveolar lavage fluid (BALF) and IgE levels in serum would be higher in RAO-affected than in healthy horses living in the same environment. Therefore, IgE-positive (+) cells were identified by immunocytochemistry on cytospins from BALF and counted. IgE levels against the mould extracts Aspergillus fumigatus (Asp. f.) and Alternaria alternata (Alt. a.) and the recombinant mould allergen Aspergillus fumigatus 8 (rAsp f 8) were measured by enzyme-linked immunosorbent assay (ELISA) in the sera of seven RAO-affected and 22 clinically healthy mature horses housed in the same conventional stable environment. After correcting for the number of neutrophils, there were no significant differences in IgE+ cells on cytospins from BALF between both groups of horses (5% versus 7%, P > 0.1). Serum IgE levels against the mould extracts were significantly higher in RAO-affected than in clinically healthy horses [median = 119 versus 66 relative ELISA units (REU), P < 0.05]. Furthermore, significantly more RAO-affected than healthy horses had detectable serum IgE against the recombinant allergen rAsp f 8 (4/7 and 3/22, respectively, P < 0.05). Age had no significant effect on BALF cell ratios or on specific serum IgE levels. These results show that high IgE levels against mould antigens are associated with RAO under controlled environmental conditions but ranges of mould-specific serum IgE levels overlapped too much between diseased and clinically healthy animals to be of any diagnostic value. Further studies are needed to assess whether IgE-mediated reactions contribute to the pathogenesis of RAO.

Mast cells and IgE-bearing cells in lungs of RAO-affected horses.

Recurrent airway obstruction (RAO) is a common condition in stabled horses characterised by small airway inflammation and obstruction following exposure of susceptible horses to mouldy hay and straw. The aim of the present study was to investigate whether lung tissue from horses with RAO contains higher numbers of IgE-protein positive (+) cells and mast cells compared to controls after mouldy hay challenge. Furthermore, mast cell subtypes in lung tissue were investigated. IgE+ cells were detected in most lung tissue samples but no significant differences between RAO-affected and control horses were found. In the wall of the bronchi and bronchioli of both RAO-affected and control horses, mainly chymase+ mast cells (MC(C)) were present (85% in the bronchial wall and 77% in the wall of the bronchioli), while 73% of the mast cells (MC) around blood vessels were tryptase+ mast cells (MC(T)). No double stained MCs were detected. RAO-affected horses had significantly more MC(C) than controls in the wall of the bronchi (median=7.6 and 1.7 cell/mm(2), respectively, P< or =0.05). They also showed a tendency for more MC(C) in the wall of the bronchioli than controls (median=21 and 2.9 cells/mm(2), respectively, P=0.07) but there were no differences in MC(T) numbers. The data suggest an involvement of MC(C) in the pathogenesis of RAO. Independently of the clinical diagnosis, there was a significant relationship between high MC(C) numbers in the bronchial wall and lung fibrosis, suggesting that these MC(C) may be involved in tissue remodelling. Furthermore, high MC(C) numbers were also associated with increased infiltration with lymphocytes and neutrophils.

Immunoglobulin-E-bearing cells in skin biopsies of horses with insect bite hypersensitivity.

The aim of the present study was to investigate, with immunohistochemistry and in situ hybridisation, if immunoglobulin-E (IgE) and mast cells are involved in the pathogenesis of insect bite hypersensitivity (IBH), an allergic 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/mm2, respectively; P < or = 0.01). More IgE-mRNA positive (+) cells were observed in the dermis of acute IBH lesions than in the dermis of healthy skin (median = 2.8 vs. 0.0 cells/mm2; P < or = 0.01). Significantly, more mast cells were detected with metachromatic (median = 160 vs. 62 cells/mm2; P < or = 0.001) and tryptase-specific stainings (median = 120 vs. 69 cells/mm2; P < or = 0.001) in the dermis 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 compared to dermatomycosis (DM) lesions; IBH biopsies contained a similar number of IgE-protein+ cells to DM biopsies (median = 249 vs. 192 cells/mm2; P = 0.08) but had significantly more IgE-mRNA+, metachromatic and tryptase+ mast cells than DM biopsies. This study suggests an involvement of IgE-mediated immune reactions in the pathogenesis of IBH as well as, sometimes, in dermatomycosis. Using double labelling, cells which expressed IgE protein and contained mast cell enzymes were detected.