Severe asthma in horses is associated with increased airway innervation

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.

To characterize peribronchial innervation in horses with asthma. We hypothesized that airway innervation increases in horses with asthma compared with controls.

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.

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.

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).

Asthma in horses is associated with greater airway innervation, possibly contributing to airway smooth muscle remodeling and exacerbating severity of the disease.