In vitro allergen-induced degranulation of pulmonary mast cells from horses with recurrent airway obstruction (heaves).

This study investigates the role of pulmonary mast cells in triggering allergic reactions in horses with a condition called recurrent airway obstruction (heaves). The research found that these cells in affected horses are more prone to release histamine – a marker of allergic reactions – when exposed to certain allergens, potentially contributing to the onset of heaves.

Research Purpose

• The research aimed to find out the degree to which pulmonary mast cells (PMC) degranulate – release granules of allergenic substances like histamine – in response to potential allergens in horses suffering from recurrent airway obstruction (heaves) and in normal horses, both before and after exposure to moldy hay.

Research Methodology

• The study incorporated five horses with diagnosed heaves and five deemed clinically normal.
• Heaves condition was identified by a marked respiratory score and an elevated change in transpulmonary pressure of more than 20 cm H2O upon exposure.
• Bronchoalveolar lavage – a procedure to clear the airways – was performed.
• Exposed cells were then subjected to various potential allergens including whole reconstituted freeze-dried mixtures of certain types of fungi, fungal extracts, and certain compounds like A23187 and 48/80 for 20 minutes at 37 degrees Celsius.
• Histamine release (HR) was measured to signal degranulation.

Research Findings

• The HR in heaves-affected horses was significantly higher in response to the above allergens, indicating more degranulation of PMC, when compared to the normal horses.
• This increased histamine release was recorded during both remission and exacerbation phases of heaves condition.
• Specifically, significant histamine release happened in heaves-affected horses due to Alternaria tenuis extract only during the exacerbation phase.
• Pulmonary mast cells also reacted and released histamine under varying medium osmolality and upon exposure to A23187, but the cells were disintegrated (lysis) by compound 48/80.

Research Implications and Conclusion

• The findings suggest that increased degranulation of PMC upon antigenic challenges might be central in driving recurrence of heaves in horses. This understanding could help in the future prevention and treatment of heaves.
• This implies that methods designed to reduce degranulation of pulmonary mast cells could be beneficial for managing heaves in horses.