Increased interleukin-1β mRNA expression in skin biopsies of horses with Culicoides hypersensitivity following challenge with Culicoides nubeculosus extract

Interleukin-1β (IL-1β) is a primary cytokine of the skin that has a pivotal role in keratinocyte differentiation, epidermal wound healing and host defense. Pathological increase of cutaneous IL-1β is associated with edema formation, epidermal hyperproliferation and atopic dermatitis in humans. However, in horses the role of cutaneous IL-1β in edema formation and allergic skin disease has not been characterised so far. Particularly in Culicoides hypersensitivity (CHS), intradermal injection of Culicoides extract may be associated with enhanced transcription of local IL-1β. To examine the mRNA expression of IL-1β and its receptor antagonist IL-1RA in the skin of horses, biopsy specimens of horses affected and non-affected by CHS prior and following intradermal challenge with a commercial C. nubeculosus extract were examined. Our hypothesis was that cutaneous IL-1β mRNA was significantly upregulated in horses with CHS in response to Culicoides allergen. Biopsies were taken from sites prior to and 4 h following intradermal challenge with C. nubeculosus extract. In order to obtain reliable data, real time PCR was performed and genes of interest were normalized using three different housekeeping genes, β-actin, GAPDH, β-2-microglobulin. No significant difference was detected in non-challenged cutaneous IL-1β mRNA and IL-1RA mRNA levels between CHS affected and non-affected horses. Intradermal injection of C. nubeculosus extract resulted in local upregulation of IL-1β mRNA both in horses with typical history, characteristic clinical signs for CHS and a positive intradermal skin test (IDT), and non-affected horses with a negative IDT. However, the difference in prior and post challenged site IL-1β mRNA levels only reached statistical significance in the affected horses (p = 0.01 versus 0.7). In contrast, IL-1RA mRNA levels did not demonstrate any modification following intradermal injection with C. nubeculosus in either group. In contrast to human atopic dermatitis, clinically normal skin of horses affected by CHS is not characterized by increased maintenance levels of IL-1β mRNA. C. nubeculosus stimulates local IL-1β transcription in all horses independent from disease, but the extent of upregulation from basal levels only reaches statistical significance in horses affected by CHS and active stage of disease.