Immunohistochemical characterization of granulomatosis with polyangiitis exhibiting spontaneous regression

Background Granulomatosis with polyangiitis (GPA) is characterized by granulomatous inflammation, vasculitis, and elevated levels of serum proteinase 3 (PR3)-anti-neutrophil cytoplasmic antibody (PR3-ANCA). Objective We tried to characterize immune cells accumulated into the lung lesions of a GPA patient exhibiting spontaneous regression. Methods Transbronchial lung biopsy (TBLB) samples were subjected to immunohistochemical analyses. Results Multiple lung nodules were detected by CT. TBLB showed granulomatous inflammation and small vessel vasculitis. This case was diagnosed as GPA based on pathological findings and elevation of PR-3 ANCA levels. Spontaneous disappearance of multiple lung nodules was observed in CT. CD3+ T cells and CD20+ B cells accumulated in the inflammatory lesions surrounding the vessels whereas granulomatous inflammation was mainly comprised of CD3+ T cells and CD68+ macrophages, but not B cells or myeloperoxidase+ neutrophils. Conclusions We characterized immune cell compositions of the lung lesions of a patient with GPA exhibiting spontaneous regression.