Role of keratinocytes in the pathogenesis of equine insect bite hypersensitivity

Equine insect bite hypersensitivity (IBH) is the most common skin disease affecting horses. It is described as an IgE-mediated, type I hypersensitivity reaction to salivary gland proteins of Culicoides insects. Together with Th-2 cells, the epithelial barrier cells play an important role in development of type I hypersensitivities. In order to elucidate the role of equine keratinocytes in development of IBH, we stimulated keratinocytes derived from IBH-affected (n=9) and healthy horses (n=9) with IBH causative-Culicoides allergens, allergic cytokine milieu and a Toll like receptor ligand 1/2 (TLR-1/2-L), and investigated their transcriptomes. Stimulation of keratinocytes with IBH-causative allergens did not induce any changes in the transcriptome of keratinocytes. However, when stimulated with allergic cytokine milieu, their gene expression significantly changed. We found upregulation of genes encoding for CCL5, -11, -20, -27 and interleukins such as IL31 known to be involved in development of type I hypersensitivities in humans. We also found a strong downregulation of genes involved in the formation of epithelial barrier. Following stimulation with TLR-1/2-L keratinocytes significantly upregulated expression of genes affecting Toll like receptor and NOD-receptor signaling pathway as well as NF-kappa B signaling pathway, among others. Transcriptomes of non-stimulated or IBH-KER and H-KER stimulated with allergic cytokine milieu were very similar and re report only 27 differentially expressed genes (DEGs). IBH-KER and H-KER stimulated with TLR-1/2-L, only seven genes were significantly differentially expressed.