Association of M2 Macrophages, Th2, and B Cells With Pathomechanism in Microscopic Polyangiitis Complicated by Interstitial Lung Disease.

Objective: To address the pathomechanism of microscopic polyangiitis (MPA) complicated by interstitial lung disease (ILD) using serum biomarker profile and pulmonary histopathology.

Methods: Serum biomarkers from patients with MPA-ILD (n = 32), MPA without ILD (n = 17), and healthy controls (n = 10) were examined. Based on the biomarker profiles, principal component analysis (PCA) and cluster analysis were performed to classify patients with MPA-ILD into subgroups. Clinical characteristics and prognosis were assessed for each subgroup. Two lung biopsies were examined following H&E staining and immunostaining.

Results: T cell and macrophage polarization was skewed toward the T helper (Th) 2 cells and M2 macrophages in the MPA-ILD group relative to that in MPA without ILD group. The PCA allowed classification of the 19 biomarker profiles into 3 groups: (1) B cell- and neutrophil-related cytokines, vascular angiogenesis-related factors, extracellular matrix-producing factors; (2) Th1-driven cytokines, M1 macrophage-driven cytokines, and Th2-driven cytokines; and (3) M2 macrophage-induced and driven cytokines. The cluster analysis stratified the patients with MPA-ILD into clinically fibrotic-dominant (CFD) and clinically inflammatory-dominant (CID) groups. Notably, severe infections were significantly higher in the CFD group than in the CID group. Immunohistochemical staining demonstrated intense CXC motif chemokine ligand 13 staining in B cells and Th2 cells in the interstitium of the lungs of patients with MPA-ILD.

Conclusion: The activation of M2 macrophages, Th2 cells, and B cells plays a key role in the pathomechanism of MPA-ILD. Classification of MPA-ILD based on serum biomarker profile would be useful in predicting the disease activity and the complications of severe infection in MPA-ILD.