IL4 and interstitial lung disease: Although both CTD-ILD and IPF converge on fibroblast activation and progressive fibrosis, their upstream cytokine milieus diverge: CTD-ILD is characterized by adaptive immune skewing with heightened type I IFN signatures, BAFF-mediated B-cell survival, the JAK/STAT pathway, and IL-6–driven inflammation, whereas IPF is characterized by type-2 inflammation and downstream IL-13/IL-4–M2 macrophage loops.