Pathological Th2 cell activation via STAT6 pathway for pulmonary fibrosis.

Idiopathic pulmonary fibrosis is a progressive and fatal lung disease in which type 2 immunity has been implicated, yet the upstream signals that sustain pathogenic T helper 2 (Th2) programs and coordinate immune-stromal remodeling remain incompletely defined. We integrated single-cell RNA sequencing from human fibrotic lungs with complementary mechanistic studies in the bleomycin mouse model to test whether CD28 costimulation engages JAK1/STAT6 signaling to drive fibrogenic inflammation. Transcriptomic analyses identified expansion of Th2 cells with elevated CD28 expression and increased STAT6 pathway activity in human IPF and bleomycin-injured mouse lungs, accompanied by transcriptional programs consistent with profibrotic monocyte-derived alveolar macrophages and activated fibroblasts. To establish causality and therapeutic relevance, we perturbed this axis in vivo after injury initiation. Antibody-mediated CD28 blockade, pharmacologic STAT6 inhibition, and genetic STAT6 deficiency each reduced Th2 accumulation and monocyte-derived alveolar macrophages, diminished collagen deposition and histologic fibrosis, and improved lung mechanics. Conversely, agonistic CD28 engagement amplified Th2 and myeloid profibrotic responses, increased collagen accumulation, and worsened pulmonary function. Across species and interventions, changes in Th2-associated signaling tracked with downstream profibrotic myeloid and stromal programs, supporting a coordinated circuit linking adaptive costimulation to fibrotic remodeling. These findings define a CD28-JAK1/STAT6-Th2-monocyte-derived alveolar macrophage pathway as a mechanistic driver of pulmonary fibrosis and nominate CD28 and STAT6 as actionable immunologic targets that could complement existing antifibrotic therapies.