Severe asthma in horses is associated with increased airway innervation

Abstract

Abstract Background Altered innervation structure and function contribute to airway hyperresponsiveness in human asthma, yet the role of innervation in airflow limitation in asthma in horses remains unknown. Hypothesis To characterize peribronchial innervation in horses with asthma. We hypothesized that airway innervation increases in horses with asthma compared with controls. Animals Formalin‐fixed lung samples from 8 horses with severe asthma and 8 healthy horses from the Equine Respiratory Tissue Biobank. Ante‐mortem lung function was recorded. Methods Blinded case‐control study. Immunohistochemistry was performed using rabbit anti‐s100 antibody as a neuronal marker for myelinating and non‐myelinating Schwann cells. The number and cumulative area of nerves in the peribronchial region and associated with airway smooth muscle were recorded using histomorphometry and corrected for airway size. Results Both the number (median [IQR]: 1.87 × 10−5 nerves/μm2 [1.28 × 10−5]) and the cumulative nerve area (CNA; 1.03 × 10−3 CNA/μm2 [1.57 × 10−3]) were higher in the peribronchial region of horses with asthma compared with controls (5.17 × 10−6 nerves/μm2 [3.76 × 10−6], 4.14 × 10−4 CNA/μm2 [2.54 × 10−4], Mann‐Whitney, P = .01). The number of nerves within or lining airway smooth muscle was significantly higher in horses with asthma (4.47 × 10−6 nerves/μm2 [5.75 × 10−6]) compared with controls (2.26 × 10−6 nerves/μm2 [1.16 × 10−6], Mann‐Whitney, P = .03). Conclusions and Clinical Importance Asthma in horses is associated with greater airway innervation, possibly contributing to airway smooth muscle remodeling and exacerbating severity of the disease.

Keywords

• heaves
• horses
• immunohistochemistry
• nerves
• remodeling