Abstract
Introduction
The recent literature suggests that mastocytic/eosinophilic inflammatory airway disease (IAD), as characterised by bronchoalveolar lavage fluid (BALF) cytology, occurs with a higher prevalence than previously reported. Data from our hospital confirms that BALF mast cell relative percentages > 2% are common, and often occur without clinical signs suggestive of airway hyperreactivity (AHR). Alterations in airway function as measured by pulmonary function testing (PFT) and/or the measurement of specific inflammatory cell mediators within the BALF may more accurately reflect AHR. This study examined the relationship between AHR, relative mast and eosinophil cell percentage, total mast and eosinophil cell concentration, and mast cell tryptase (MCT) concentration in BALF.
Materials and methods
Twenty four healthy adult sedentary horses were included in the study (ethics approval R2423/11). PFT with histamine bronchoprovocation was undertaken using a commercial flowmetric plethysmography system (Open Pleth™). BAL was performed as previously described in the literature in horses ≤ 16 hours after PFT. Total nucleated cells counts and relative cellular percentages of cells were determined using examination of 400 cells. Horses were categorised as having IAD if a relative neutrophilia (>5%) and/or a relative eosinophilia (≥1%) and/or a relative mastocytosis (>2%) were present. MCT was measured from the BALF supernatant using a commercial ELISA (EIAab Inc). Statistical analysis was used to determine associations between total cell count and relative percentages of mast cells, eosinophils, PC35 (an objective measure of bronchoprovocation), and MCT concentration. Data were then categorised to investigate the level of association.
Results
AHR was demonstrated in 53% of horses. Of the horses with IAD (92%) as determined by BALF cytology, the majority had mixed inflammatory cell profile. Neither the relative cell percentages nor the total numbers of mast or eosinophils cells were significantly correlated with AHR, but MCT was significantly correlated with AHR (p=0.05). MCT concentration was not correlated with relative mast percentage or total mast cell count, but was positively correlated with relative eosinophil percentage and the total eosinophil cell concentration (p≤0.05). When data were categorised, MCT concentration was significantly greater in the mastocytosis group (>2%) (p≤0.05), but was not significantly different between the mast cell 2-5% group and the mast cell >5% group. Those horses that were categorised as having a combined mixed mast cell, eosinophilic, neutrophilic response had a significantly higher MCT than all other responses (p≤0.05). Relevance to clinical equine practice It was concluded in this population of horses that the relative mast or eosinophil percentage may not be indicative of AHR. It is plausible that cells, although present in higher numbers, could be quiescent in the respiratory tract. A mixed mast cell inflammatory response may indicate an active release of MCT and an associated increased AHR. Given the often vague clinical signs of equine IAD, care should be taken in using existing global cytological definitions of BALF cytology as the sole method of confirming the diagnosis of disease in Australia.