TABLE 1.

Common triggers for asthma exacerbations are mediated by different pathways, frequently involving steroid-unresponsive neutrophils and CD8 cells

	Allergen exposure	Viral infection	Ozone/diesel exhaust	Cigarette smoke	Bacterial infection
Predominant pathway	Th2 cells, IgE	Th1 cells, leukotrienes	Th1 cells, leukotrienes	Th1 cells, leukotrienes	Th17 cells, IL-1β, IL-6, TNF
Predominant effector cells	Eosinophils, Mast-cells, CD4 T-cells	Neutrophils, CD8 T-cells	Neutrophils, CD8 T-cells	Neutrophils, CD8 T-cells	Neutrophils
Steroid responsiveness	High	Low	Low	Low	Low

Th1/2 cells: type 1/2 CD4⁺ T-cells; IL: interleukin; TNF: tumour necrosis factor.