Toll‐like receptor‐ligand induced thymic stromal lymphopoietin expression in primary equine keratinocytes

Background Thymic stromal lymphopoietin (TSLP) plays a key role in the development of allergic inflammation. Little is known about possible triggers of equine TSLP expression. Hypothesis/objectives To investigate TSLP expression in equine insect bite hypersensitivity (IBH) skin lesions. The capacity of TLR 1‐8 ligands (L) and of atopic cytokine milieu as potential triggers of TSLP and of interleukin (IL)‐6 as a downstream effector molecule of TLR signalling, were examined in primary equine keratinocyte cultures. Animals Lesional skin from IBH‐affected and healthy skin from control‐horses (n = 9 each group) was sampled. Methods and materials Keratinocyte cultures were established from six healthy horses and stimulated with TLR 1‐8‐L, and with IL‐4 and tumor necrosis factor‐α, to mimic an atopic inflammation cytokine milieu. TSLP and IL‐6 gene expression was assessed by quantitative real‐time PCR. Results Expression of TSLP was significantly greater in IBH lesions compared to healthy skin. TLR 1‐8‐L significantly upregulated TSLP expression in keratinocytes. The strongest upregulation was induced by TLR 1/2‐L and TLR 3‐L. Combination of atopic cytokine milieu and TLR 1/2‐L or TLR 3‐L further increased TSLP expression. TLR‐L 1‐5 stimulation significantly upregulated IL‐6 expression. Conclusions and clinical importance The data herein suggest that the upregulation of TSLP expression in lesional skin of IBH‐affected horses might play a role in IBH development. Moreover, TSLP expression is induced by TLR‐L, in particular by TLR 1/2‐L and TLR 3‐L, and is further increased by atopic cytokine milieu, indicating a mechanism for TSLP‐mediated exacerbation of IBH. Résumé Contexte Le TSLP (Thymic stromal lymphopoietin) joue un rôle clé dans le développement de l'inflammation allergique. On en sait peu sur les facteurs possibles d'expression de TSLP chez le cheval. Hypothèses/objectifs Étudier l'expression de TSLP dans les lésions cutanées de l'hypersensibilité aux piqures d'insectes (IBH) chez le cheval. La capacité des ligands TLR 1‐8 (L) et des cytokines atopiques comme déclencheurs potentiels de TSLP et d'interleukine (IL)‐6 comme molécule effectrice de régulation du signal TLR, ont été examinés dans des cultures de kératinocytes équins primaires. Sujets La peau lésionnelle d’IBH atteints et de peau saine de chevaux contrôles (n=9 pour chaque groupe) a été prélevée. Matériel et méthodes Les cultures de kératinocytes ont été réalisées à partir de six chevaux sains et