Abstract
Introduction: Idiopathic pulmonary fibrosis (IPF) arises from repetitive epithelial injury, fibroblast activation, immune dysregulation, and excessive extracellular matrix deposition, driving fibrosis. Evidence implicates adaptive immune dysfunction in disease progression. Tertiary lymphoid structures in fibrotic lung tissue, together with circulating autoantibodies, suggest aberrant B cell activation and loss of immune tolerance in IPF pathogenesis.
Aim: To characterise peripheral blood T cell phenotypes and cytokine profiles in patients with IPF versus age-matched healthy controls.
Method: Flow cytometric analysis and cytokine profiling was conducted on peripheral blood from IPF cases (n = 20, flow cytometry; n = 57, cytokine analysis) and age-matched controls (n = 23, n = 21, respectively). White blood cells were isolated, cryopreserved, and analysed by spectral flow cytometry (Cytek Aurora) using a 12 antibody panel to define CD4,+ CD8+, T regulatory cells, T follicular helper cells, Th17, activated, and naïve/memory T cell subsets. Serum cytokines were measured using a human 42-plex ProcartaPlex Panel and custom ProcartaPlex immunoassays (ThermoFisher Scientific).
Results: Flow cytometry demonstrated increased circulating CD8+ T cells (33.1% ±SD 16.4 vs. 25.7% ±SD 11.5) and CD4+CD8+ double-positive T cells (1.45% ±SD 1.16 vs. 0.85% ±SD 0.55) in cases with IPF compared to controls. There were increased levels of cytokines associated with CD8+ T cell activation (IFN-γ) and B cell proliferation, maturation, differentiation, antibody production and isotype class switching (IL-6, sCD40L, BAFF, April, IL-21 and IL-13) in IPF. Elevations in cytokines involved in neutrophil recruitment and activation (IL-8 and IL-17A), monocyte/lymphocyte chemotaxis (MCP-2) and tissue remodelling (sST2) were similarly observed in IPF serum.
Conclusion: Patients with IPF show selective expansion of CD8+ and double-positive T cells. Increased cytokines linked to B cell activation, neutrophil recruitment, and tissue remodelling may promote crosstalk between innate and adaptive immunity. CD4+ T cells may enhance B cell activation, plasmablast differentiation, and autoantibody production, while CD8+ T cells could amplify epithelial injury and fibroblast activation.
Grant Support: National Health and Medical Research Council (NHMRC).