T-cell responses in asthma exacerbations

Objective: Asthma is a chronic lung disease comprising multiple endotypes and characterized by periodic exacerbations. A diverse array of T cells has been found to contribute to all endotypes of asthma in pathogenic and regulatory roles. Here, we review the contributions of CD4+, CD8+, and unconventional T cells in allergic and nonallergic asthma.

Data sources: Review of published literature pertaining to conventional and unconventional T-cell types in asthma.

Study selections: Recent peer-reviewed articles pertaining to T cells in asthma, with additional peer-reviewed studies for context.

Results: Much research in asthma has focused on the roles of CD4+ T_H cells. Roles for T_H2 cells in promoting allergic asthma pathogenesis have been well-described, and the recent description of pathogenic T_H2A cells provides additional insight into these responses. Other T_H types, notably T_H1 and T_H17, have been linked to neutrophilic and steroid-resistant asthma phenotypes. Beyond CD4+ T cells, CD8+ Tc2 cells are also strongly associated with allergic asthma. An emerging area for study is unconventional T-cell types, including γδT, invariant natural killer T, and mucosal-associated invariant T cells. Although data in asthma remain limited for these cells, their ability to bridge innate and adaptive responses likely makes them key players in asthma. A number of asthma therapies target T-cell responses, and, although data are limited, they seem to modulate T-cell populations.

Conclusion: Given the diversity and heterogeneity of asthma and T-cell responses, there remain many rich avenues for research to better understand the pathogenesis of asthma. Despite the breadth of T cells in asthma, approved therapeutics remain limited to T_H2 networks.