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

This research investigated whether immunoglobulin-E (IgE) and mast cells play a role in causing insect bite hypersensitivity (IBH), an allergic skin condition in horses. The results indicated a higher presence of IgE protein-bearing cells and mast cells in acute and chronic IBH cases compared to healthy horses, suggesting that IgE-mediated immune reactions might be involved in the development of this allergy.

Objective of the Study and Methodology

• The primary goal of the study was to figure out if immunoglobulin-E (IgE) and mast cells contribute to the development of insect bite hypersensitivity (IBH), an allergic skin disease in horses.
• The researchers used immunohistochemistry and in situ hybridisation techniques to investigate this.
• Skin biopsies from horses with both acute and chronic cases of IBH, as well as from healthy horses, were collected. The samples were then fixed in paraformaldehyde (PFA) for less than 24 hours.

Findings on IgE Protein-Bearing and IgE-mRNA Positive Cells

• In tissue sections fixed in PFA for less than 24 hours, there were significantly more IgE protein-bearing cells in the dermis and epidermis of acute and chronic IBH lesions than in skin biopsies from healthy horses.
• More IgE-mRNA positive cells were found in the dermis of acute IBH lesions than in the dermis of healthy skin.

Mast Cell Presence

• In addition to higher levels of IgE protein-bearing and IgE-mRNA positive cells, they found significantly more mast cells in the dermis of acute IBH biopsies compared to healthy skin. These cells were detected using metachromatic and tryptase-specific stainings.
• Interestingly, no chymase+ mast cells were found in any skin biopsy, indicating this type of mast cell does not play a role in IBH reactions.

Comparisons to Dermatomycosis Lesions

• IBH lesions fixed in PFA for more than 24 hours were compared to lesions of dermatomycosis (DM), a type of fungal infection of the skin.
• The IBH biopsies showed a similar number of IgE protein-bearing cells when compared to DM biopsies.
• However, there were significantly more IgE-mRNA positive cells and metachromatic and tryptase+ mast cells in IBH biopsies than in DM biopsies.

Conclusion

• The study suggests the involvement of IgE-mediated immune reactions in IBH’s development, and sometimes, dermatomycosis.
• Using double labelling, cells that expressed IgE protein and contained mast cell enzymes were identified, reinforcing the correlation between IgE and mast cells in IBH reactions.