Altered sputum granzyme B and granzyme B/proteinase inhibitor-9 in patients with non-eosinophilic asthma

Background and objectiveThe non-eosinophilic phenotype of asthma (NEA) is associated with chronic airway inflammation and airway neutrophilia. An accumulation of apoptotic airway epithelial cells, if not efficiently cleared by efferocytosis, can undergo secondary necrosis, with the potential for inflammation of surrounding tissues. Apoptosis may occur via the T cell granzyme B pathway. The role of granzyme B in NEA is not known. The aim of this study was to investigate production of granzyme B and its inhibitor proteinase inhibitor (PI)-9 by T cells from induced sputum and compare expression between eosinophilic, NEA and healthy controls.

MethodsWe investigated T cell intracellular granzyme B and its inhibitor, PI-9, in sputum from healthy control subjects (n=10), and patients with NEA (n=22) or eosinophilic asthma (EA) (n=15) using flow cytometry.

ResultsGranzyme B expression and the ratio of granzyme B to PI-9 positive cells were highest in those with NEA for both CD3+ and CD4+ T cells. The expression of granzyme B was not statistically different between patients with NEA and EA; however, the ratio of granzyme B to PI-9 positive cells for CD3+ T cells was significantly higher in those with NEA compared with EA.

ConclusionsInduced sputum provides a non-invasive tool for investigating T cell cytotoxic mediators in the various asthma subtypes. Granzyme B expression is increased in NEA and the contribution of granzyme B to chronic inflammation requires further study.

The non-eosinophilic phenotype of asthma is associated with chronic airway inflammation and airway neutrophilia. The role of granzyme B in NEA is not known. Increased granzyme B expression in NEA may contribute to increased epithelial cell apoptosis, lung injury and chronic inflammation.