Serum Tryptase and Sputum Cellular Profile in Relation to Asthma Severity

Rationale: Tryptase is released by mast cells (MC) along with histamine and serves as a marker of MC activation, which in turn contributes to asthma development, severity and tissue remodeling as well. The objective of this study is to investigate the potential role of MC activation and sputum cellular profile (CP) in asthma severity.

Methods: Based on spirometric FEV₁%, subjects aged 20-40 years old were grouped into mild/moderate asthma group (mild/moderate group) (n=15), severe asthma group (severe group) (n=15) and healthy control group (control) (n=15). All groups have been subjected to clinical examination, plain chest x-ray, CBC, total serum IgE (tIgE), serum b-tryptase assay and induced sputum CP.

Results: A significant reduction in FEV₁% was demonstrated in mild/moderate and severe groups compared with control (mean±SD: 74.8±3.1, 65±3 & 84.7±2.3 respectively, p<0.0001). b-tryptase and tIgE, revealed a significant increase in mild/moderate and severe groups compared with control (b-tryptase: mean±SD: 4.8±1 & 13.3±10.6, p<0.001 & 0.0001 respectively, tIgE: mean±SD: 324.2±137.1 & 2433.4±880.5 respectively, p<0.0001 for both asthma groups). Significant sputum monocytosis was only evident in mild/moderate asthmatics compared with control (mean±SD: 87.4±78.2 & 30.3±14.4, p=0.01), indicating increased sputum monocyte/macrophage lineage in this group. While, severe group as compared to control, expressed a significant rise in sputum neutrophil CP (mean±SD: 248.5±97.5 & 173.3±82.2 respectively, p=0.03). The mild/moderate group in comparison with control, showed significant blood eosinophilia (mean±SD: 0.2±0.1 & 0.1±0.08 respectively, p<0.0001) and monocytosis (mean±SD: 0.5±0.2 & 0.1±0.1 respectively, p<0.0001).

Conclusions: MC activation with increased b-tryptase and sputum neutrophilic CP may reflect asthma severity.