Th2 cell markers in peripheral blood increase during an acute asthma exacerbation

Allergic asthma is characterized by type 2 inflammation. We have shown the presence of increased type 2 inflammation in patients with severe asthma and those with frequent exacerbations. However, it is not known whether increased type 2 inflammation drives asthma exacerbations. This study aims to determine Th2 immune parameters in patients presenting to the emergency department (ED) with an acute asthma exacerbation and correlate these parameters with clinical and physiological measures of asthma.

Sixteen adults presenting to the ED with acute asthma exacerbations were recruited after giving informed consent. Ten patients returned 2 weeks later for follow-up. Physiological parameters, asthma control (ACQ6), asthma quality of life (AQLQ) questionnaires, and venous blood were collected during both visits. An immune cell profiling was performed by whole blood flow cytometry: CD4⁺ T cells, Th2 cells (CD4⁺ CRTh2⁺ T cells and % of CD4⁺ T cells expressing CRTh2), eosinophils and innate lymphoid cells (ILC2).

During exacerbation, peripheral blood Th2 cell numbers correlated with ACQ6 and AQLQ scores, while ILC2 and eosinophil numbers did not. Subjects had higher % of CD4⁺ T cells expressing CRTh2 and worse FEV₁ during exacerbation compared with the follow-up. The decrease in the % of CD4⁺ T cells expressing CRTh2 seen during the follow-up visit correlated with the improvement in lung function.

These data suggest that Th2 cells in peripheral blood may be a sensitive measure of increasing symptoms in patients with asthma exacerbations and may serve as a biomarker of an asthma exacerbation.