Meaning of IgG4-positive plasma cells in interstitial pneumonia

What is it about?

There have been few reports on immunoglobulin-G4 (IgG4)-related interstitial pneumonia (IP), and its clinical features remain unclear. The objective of this study was to assess whether IP with marked IgG4-positive plasma cell infiltration without extrathoracic lesions of IgG4-related disease (RD) should be diagnosed as a subtype of IgG4-RD or a separate entity.

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Photo by Noah Negishi on Unsplash

Photo by Noah Negishi on Unsplash

Why is it important?

All consecutive patients with surgical lung biopsy-proven idiopathic IP with an IgG4/IgG-positive cell ratio of >40% and >50 IgG4+ plasma cells in a high-power field without extrathoracic lesions of IgG4-RD were retrospectively reviewed. Five patients were enrolled in this study. All patients were male with a history of smoking. Four patients met the comprehensive diagnostic criteria for IgG4-RD. The remaining one lacked data related to the serum IgG4 level. Histologically, a nonspecific IP pattern was observed in all patients. The key morphologic features of IgG4-RD, such as storiform fibrosis and obliterative phlebitis with lymphoplasmacytic infiltration in a loose background texture, were absent in every patient. In contrast, venule obstruction by densely packed lymphoplasmacytic infiltration was observed in two patients. Marked scarring and remodelling of the lung were also noted, which is not typically seen in IgG4-RD. A favourable response to corticosteroid monotherapy was observed in all patients; however, two patients developed lung cancer during the course of observation. In this study, we studied five patients with IP with marked IgG4-positive plasma cell infiltration without extrathoracic lesions of IgG4-RD. However, we hesitate to conclude that the five patients presented here represent IgG4-RLD cases because their histopathological findings differed from those of previously reported IgG4-RD cases in terms of the following points: (1) absence of storiform fibrosis, (2) marked scarring and remodelling of the lung and (3) obstruction of arteries and veins by densely packed lymphoplasmacytic infiltration.

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