We read with interest the paper of Chandra et al. (1) reporting the frequency of invariant NKT (iNKT) and mucosal-associated invariant T (MAIT) cells in blood samples obtained from children at age 1 y and their possible correlation with recurrent wheezing, allergen sensitization, and asthma at ages 3 or 7 y. The authors suggested that high iNKT cell antigenic activity could be a marker of houses with increased microbial exposures and also with protection from asthma. The role played by iNKT cells in asthma is still unclear. Our previous paper demonstrated that the frequency of iNKT cells was enhanced in bronchoalveolar lavage fluid of severe asthmatic children, indicating their possible implication on asthma severity (2).
Concerning MAIT cells, Chandra et al. (1) showed that a higher MAIT cell frequency in the blood of 1-year-old children was associated with reduced risk of asthma. We recently found that the frequency of circulating IL-17A–producing MAIT cells was higher in exacerbators than in non-exacerbators among asthmatic children at the age of 11 y and positively correlated with the number of severe exacerbations (3). No significant difference was observed concerning the global percentage of MAIT cells or IFN-γ–producing MAIT cells (Fig. 1). Although our population differs from that of Chandra et al. (1), these results raise the following questions: 1) are MAIT cells friends or foes in asthma and 2) could IFN-γ– and IL-17A–producing MAIT cells play distinct roles? Because asthma is a complex and heterogeneous pathology involving Th2 and Th17 inflammatory responses, further in-depth studies are required to better understand the implication of iNKT and MAIT cells in asthma pathology.