Pulmonary emphysema in the horse in response to lung disorders associated with an
influx of neutrophils, such as chronic obstructive pulmonary disease (COPD), results
in a restricted peribronchiolar pattern of tissue damage. Humans, in contrast, have a
more extensive centrilobular pattern of emphysema in similar neutrophil associated
lung disorders. The major cause of pulmonary emphysema has been shown to be
excessive or unregulated neutrophil elastase activity which has led to the development
of the 'proteinase:anti-proteinase theory of lung disease'. To evaluate the
proteinase:antiproteinase balance in the horse in order to compare it to that found for
human API some aspects of equine neutrophil elastase (ENE) and its main regulator
in the lower respiratory tract, equine alpha-1-proteinase inhibitor (API), have been
investigated.Mouse monoclonal and sheep polyclonal antibodies specific to equine API were raised
and used to show by immunohistochemistry that the distribution of equine API was
very similar to that of the previously known distribution for human API. The major
difference between the two species was that equine hepatocytes and bile ductules
showed extensive and often intense positive staining for equine API which has not
been demonstrated in equivalent human tissues.Sheep polyclonal antibodies specific to ENE 2A, the most abundant ENE found in
equine neutrophils, were raised and used to show that ENE 2A had a granular
distribution confined to the cytoplasm of neutrophils and that each neutrophil
contained 0.813 ± 0.054 pg (mean ± SEM) of ENE2A. In contrast equine API had a
uniform non-granular cytoplasmic distribution and each neutrophil contained 0.021 ±
0.003 pg ofequine API.In dynamic studies of Percoll purified equine peripheral blood neutrophils a positive
correlation existed between the total superoxide anions (SOA) generated and release
of ENE 2A when stimulated with zymosan activated serum over 90 minutes. These
kinetic data suggest that SOA generation may have the potential to prolong the
activity of ENE 2A in the neutrophil's immediate microenvironment by promoting
oxidative inactivation of API thereby enhancing the neutrophil's contribution to local
host tissue damage. Both these secretory mechanisms were dependent upon
extracellular cations.These findings suggest that the difference in anatomical distribution of pulmonary
emphysema in horses and humans is probably due to a higher concentration of plasma
derived equine API in pulmonary epithelial lining fluid. This, combined with the
presence of oxidation resistant serine proteinase inhibitor (Spi) proteins, creates a
more efficient antiproteinase screen in the neutrophil micro-environment in equine
pulmonary tissues resulting in more effective inhibition of unwanted neutrophil
elastase activity and subsequent host tissue damage
