ACTA1 and interstitial lung disease: To elucidate the cellular localization of SIK2 within lung tissue, we conducted immunofluorescence co-staining of SIK2 with α-SMA (a myofibroblast marker) [26], SPC (a type II alveolar epithelial cell marker), and CD68 (a monocyte or macrophage marker) on lung tissue sections from patients with PF, including IPF and CTD-ILD.