Interleukin 31 mediates pruritus in horses.

OBJECTIVE: This study investigated the effects of recombinant equine IL-31 (eIL-31) in vivo and in vitro. METHODS: Equine IL-31 mRNA sequences were verified by sequencing. Recombinant eIL-31 was produced using mammalian and bacterial expression systems. From November 2019 through February 2021, 12 normal horses, 6 to 10 years old with no history or clinical signs consistent with allergic skin disease, were injected ID with eIL-31 and saline in 2 challenge studies. Pruritus-associated behaviors were recorded for a minimum of 15 minutes preinjection and 4 hours postinjection. Adherent monocytes from 3 pruritic horses, exhibiting insect bite hypersensitivity and/or atopic dermatitis, were stimulated with bacterial eIL-31, and subsequent phosphorylation of signal transducer and activator of transcription 3 (STAT3) was measured by western blot and AlphaLISA. RESULTS: The bacterial eIL-31 was produced with greater purity than the mammalian eIL-31 (> 95% vs 70%). Pruritus was elicited by both recombinant proteins. The mammalian eIL-31 induced mild pruritus (cumulative seconds spent itching postinjection ranged from 6 to 313). The bacterial eIL-31 induced marked pruritus in some horses (a cumulative maximum of 5,529 seconds spent itching in 1 horse) and a milder response in others (range of cumulative seconds spent itching, 17 to 2,313). Most pruritus occurred after 2 hours and subsided by 4 hours postinjection. Bacterial eIL-31 induced STAT3 phosphorylation in adherent monocytes from allergic horses. CONCLUSIONS: In this proof-of-concept study, IL-31 was found to mediate pruritus and was associated with STAT3 phosphorylation in horses as in other species. CLINICAL RELEVANCE: Interleukin 31 is a promising therapeutic target for equine allergic pruritus.

Trichohyalin gene expression is negatively correlated with the severity of dermatitis in a canine atopic dermatitis model.

Introduction: Canine atopic dermatitis (AD) closely mimics human AD and is recognized as a beneficial animal model. House dust mites (HDM) are a common allergen for both species. The effects of chronic exposure to HDM on the skin have not been studied in this animal model, and it is not known how changes in gene expression correlate to the severity of dermatitis. Methods: We used an established canine model of AD and took biopsies before HDM exposure (D0) and five times during repeated allergen challenges (on Days 1, 2, 8, 15, and 29, hereafter referred to as D1, D2, D8, D15, and D29). The severity of dermatitis was scored on the same days. Results: Trichohyalin (TCHH) gene expression decreased the most (15-fold decrease on D29 vs. D0) and negatively correlated with the severity of dermatitis. Gap-junction protein gene expression increased over 3-fold on D1, D8, and D29 and positively correlated with the severity of dermatitis. Compared to D0, IL-31 gene expression significantly increased on D8 (p = 0.0098), D15 (p = 0.0068), and D29 (p = 0.0187), but the correlation with the severity of dermatitis did not reach significance. Discussion: This is the first report on trichohyalin, a protein belonging to the S100 family, and gap-junction protein gene expression in the context of the clinical severity of AD. We propose that these proteins should be further investigated to better understand their role in this complex disease.

Transcription of interleukin 31 and its receptor by leukocytes after Culicoides sp stimulation is dose dependent but is not exaggerated in allergic horses or correlated with pruritus.

OBJECTIVE: Preliminary evidence supports a role for IL-31 in equine insect bite hypersensitivity (IBH) and pruritus. Our studies investigated IL-31 and IL-31 receptor-α (IL-31RA) transcription in leukocytes from normal and IBH horses in response to Culicoides nubeculosus. ANIMALS: 19 normal and 15 IBH horses were recruited in the summer of 2019 (low-dose study) and 8 normal and 10 IBH horses in the winter of 2022 to 2023 (high-dose study). Normal horses had no history or signs of allergic skin disease, while IBH horses had a history and clinical signs compatible with IBH. Pruritus was scored using a visual analog score or a 1 to 6 grading system. PROCEDURES: Whole blood leukocytes were incubated with saline (0.9% NaCl) solution or C nubeculosus (0.26 µg/mL [low dose]; 5 µg/mL [high dose]). Transcription of IL-31 and IL-31RA was measured by quantitative RT-PCR. RESULTS: Transcription of IL-31 and IL-31RA significantly increased in leukocytes from normal and IBH horses following high-dose C nubeculosus, and no differences were found between populations. Following low-dose C nubeculosus IL-31RA, transcription was increased in both normal and IBH horses, but IL-31 transcription was reduced in normal horses. No positive correlation was found between pruritus scores and IL-31 transcription after low- or high-dose C nubeculosus stimulation. CLINICAL RELEVANCE: Exaggerated IL-31 transcription was not identified in IBH horses, suggesting that dysregulation in IL-31 signaling occurs downstream or in localized tissues or involves regulation by yet unidentified receptor splice variants or IL-31-induced increased sensitivity to other pruritogens. Further studies to understand IL-31 signaling in equine allergic skin disease are needed.