Mast cells and IgE-bearing cells in lungs of RAO-affected horses.

This study investigates the role of specific types of immune cells known as mast cells and IgE-protein positive cells in the development of recurrent airway obstruction (RAO), a common respiratory condition in horses often caused by exposure to mouldy hay and straw.

Objective of the Study

• The aim of this research was to determine if horses afflicted with RAO have a higher number of IgE-protein positive cells and mast cells in their lung tissue compared to healthy horses, particularly after exposure to mouldy hay.

Methods and Findings

• Distinct subsets of mast cells, more specifically chymase-positive mast cells (MC(C)) and tryptase-positive mast cells (MC(T)), were examined in the lung tissue.
• Although IgE+ cells were noticed in most lung tissue samples, the distribution of these cells did not significantly differ between RAO-affected and unafflicted horses.
• For both groups, MC(C) were predominantly found in the walls of the bronchi and bronchioles, whereas most of the mast cells around blood vessels were MC(T). There was no evidence of double stained (both chymase and tryptase positive) mast cells.
• RAO-affected horses had significantly more MC(C) than control horses in the bronchi walls.

Implications of the Findings

• The presence of higher numbers of MC(C) in RAO-affected horses suggests their involvement in the disease’s pathogenesis.
• Regardless of whether horses were diagnosed with RAO, there was a significant correlation between high MC(C) numbers in the bronchial wall and the presence of lung fibrosis, implying a possible role for MC(C) in tissue remodelling.
• Similarly, high counts of MC(C) were related to increased infiltration of lymphocytes and neutrophils, other immune cells associated with inflammation and immune response.

Conclusions

• The study does not establish a connection between high counts of IgE+ cells and RAO, but it does indicate a potential role for MC(C) in the development and progression of the disease.
• Additional research is necessary to further explore the exact role and mechanism of these cells in RAO, which could pave the way for new therapeutic strategies to manage this common equine respiratory disorder.