**5. Conclusions**

In conclusion, the chemometric analysis methods produced robust and immunologically meaningful results, which clustered the degranulation markers (CD11b and CD63) expressed on eosinophils with the concentration of NO2 and PM2.5. Besides that, the degranulation markers expressed on the neutrophils, CD63 and CD66b, were clustered together with the PM2.5 concentration. A further prospective study is now obligatory to validate the models generated from this current study.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-4601/17/15/5413/s1, Table S1: The results of allergy skin test.

**Author Contributions:** Conceptualization, K.N.M.I., Z.H. and J.H.H.; methodology, K.N.M.I., Z.H., J.J., J.H.H. and L.T.L.T.; software, K.N.M.I.; validation, K.N.M.I., Z.H., J.J. and L.T.L.T.; formal analysis, K.N.M.I.; investigation, K.N.M.I. and Z.H.; resources, Z.H. and J.H.H.; data curation, K.N.M.I. and Z.H.; writing—original draft preparation, K.N.M.I.; writing—review and editing, Z.H. and J.J.; visualization, K.N.M.I.; supervision, Z.H.; project administration, K.N.M.I and Z.H.; funding acquisition, Z.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by High Impact Putra Grant from Universiti Putra Malaysia (UPM) (VOT 9598000).

**Acknowledgments:** The researchers are grateful to all students who had participated in this study and the grea<sup>t</sup> support and hospitality from the school teachers are much appreciated.

**Conflicts of Interest:** The authors declare no conflict of interest.
