Organic dust exposure increases mast cell tryptase in bronchoalveolar lavage fluid and airway epithelium of heaves horses.

The study examines the effect of organic dust exposure on mast cell tryptase in horses suffering from ‘heaves’, a respiratory condition akin to human asthma. The researchers discovered increased levels of tryptase in both normal and heaves-susceptible horses exposed to hay/straw challenge, with a noticeable upsurge of tryptase-expressing cells in the latter.

Objective and Hypothesis

• The research was aimed at measuring the levels of a proteinase called tryptase, released by mast cells, in the bronchoalveolar lavage fluid (BALF) of healthy and heaves-affected horses.
• The study’s hypothesis was based on the suggested role of mast cells in allergies and asthma in humans, presupposing a similar role might exist in equine heaves, closely mirroring occupational dust-induced asthma.

Methodology

• The researchers conducted their experiment by collecting BALF from control (healthy) and heaves-prone horses before and after a 24-hour hay/straw challenge (HSC) and later determining tryptase concentrations with an ELISA test.
• Tryptase mRNA and protein expression in pulmonary mast cells were studied using quantitative PCR and immunohistochemistry in bronchial and bronchiolar tissue samples from the horses.

Results

• There was a significant rise in BALF tryptase concentrations in both control and heaves-susceptible horses post-HSC.
• A marked increase in the numbers of tryptase-expressing intra-epithelial mast cells was seen in heaves-affected horses following the challenge, unlike the controls.
• Interestingly, bronchiolar tissue from heaves horses removed from the challenge showed notably lower tryptase transcripts than those in control horses.

Conclusions

• Mast cell degranulation and consequent tryptase release into the airways follow the hay/straw challenge in both control and heaves-prone horses.
• The increased number of mast cells in the bronchiolar epithelium of the affected horses might play a vital role in the pulmonary inflammatory response associated with heaves.