Clinical and pathological characteristics of IgG4-related interstitial lung disease

IgG4-related interstitial lung disease (IgG4-RILD), which is characterized by increased IgG4 levels, IgG4⁺ plasma cell infiltration and irregular whorled fibrosis, is a recently described lung disorder that belongs to the group of systemic fibroinflammatory IgG4-related diseases (IgG4-RD). The aim of the present study was to improve the current knowledge regarding the specific clinical and histopathological characteristics of IgG4-RILD and to investigate its underlying immune mechanism in vivo. A total of 7 patients newly diagnosed with IgG4-RILD were enrolled in the present study (4 men and 3 women; mean age, 57 years; range, 29-71 years). Patients' clinical history was collected and serological indicators, including C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), antinuclear antibodies (ANAs) and tumor markers were measured. Serum immunoglobulin G (IgG), IgE and IgG4 levels were also evaluated. In addition, computed tomographic (CT) images and pathological examinations were used to determine the characteristics of lung lesions in all patients. The majority of patients presented with symptoms of fever, cough and dyspnea, while allergic symptoms were also encountered. The laboratory examination results revealed different degrees of increased CRP, ESR, tumor markers, ANA, serum IgE and IgG4. The CT images revealed diffuse ground glass opacities, bronchiectasis and thickened bronchovascular bundles. Histologically, the lung lesions were characterized by dense IgG4⁺ lymphoplasmacytic infiltrates intermixed with extensive fibrous tissue hyperplasia and an irregularly storiform pattern of fibrosis. The mean number of IgG4⁺ plasma cells was >10 cells/high power field. The ratio of IgG/IgG4⁺ plasma cells was >50% in inflamed lesions and the number of parenchymal cells was markedly reduced. Obliterative phlebitis or obliterative arteritis was observed in all patients. In conclusion, the clinicopathological similarities between IgG4-RILD and other IgG4-RD suggest that IgG4-related immunopathological processes may be associated with the pathogenesis of pulmonary lesions. Future studies based on the findings herein may elucidate the specific pathological process underlying the development of this fibroinflammatory disorder.