Asthma is a chronic inflammatory disease of the airways and the mechanisms are not fully understood. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of monocytes, granulocyte and myeloid cells at early stage of differentiation. They possess phenotypic plasticity and regulate airway
inflammation. We recently reported that
Kruppel-like factor 4 (KLF4) regulates MDSC differentiation into fibrocytes, emerging effectors in chronic
inflammation. However, the role of KLF4 in
asthma is not known.
Thymic stromal lymphopoietin (TSLP) is an epithelial cell-derived
cytokine and a key initiator of allergic airway
inflammation. Given the fact that TSLP promotes Th2
cytokine production that increases MDSC differentiation into fibrocytes, we postulate that KLF4 regulates
asthma in a TSLP-dependent manner. In this study, we utilized a model of allergic
asthma with
ovalbumin challenge (OVA). We found that upon OVA treatment the wild type mice had increased MDSC infiltration into the lung, up-regulation of KLF4 and TSLP gene expression, and higher levels of Th2
cytokines including
IL4 and
IL13. Consistently, lack of KLF4 expression in monocytes and lung epithelial cells resulted in decreased TSLP expression and lower levels of Th2
cytokines in mice, and fibrocyte generation was compromised. KLF4 deficiency in these cells also led to decreased
airway hyperresponsiveness (AHR), a cardinal feature of
asthma, as assessed by whole body plethysmography. Moreover, lung
fibrosis as measured by trichome staining was attenuated and the population of CD45 + COL1A1+ fibrocytes was diminished in this setting. Together, our results suggest that KLF4 regulates
asthma development in a TSLP- and fibrocyte-dependent manner.