NOS2 and Increased total eosinophil count: However, FeNO and eosinophilia, although related, represent two distinct biomarkers resulting from two different T2 cytokine pathways: IL-4 and IL-13, which are implied in IgE synthesis and iNOS induction and thus NO production, and IL-5, which is involved in the activation, development, and recruitment of eosinophils.