IgG4positive

IgG4-positive refers to tissues or cells that stain positive for immunoglobulin G4 (IgG4) by immunohistochemistry, indicating the presence of IgG4-producing plasma cells. The term is most often used in the context of IgG4-related disease (IgG4-RD), a chronic fibroinflammatory condition that can affect multiple organs.

In IgG4-related disease, histopathology typically shows a dense lymphoplasmacytic infiltrate rich in IgG4-positive plasma cells, storiform fibrosis, and obliterative phlebitis. Pathologists use quantitative criteria that vary by organ, including the proportion of IgG4-positive plasma cells among IgG-positive cells and the absolute number of IgG4-positive cells per high-power field. Thresholds for these metrics are not uniform across all tissues.

Serum IgG4 concentration is elevated in many cases of IgG4-RD but is not universal, and normal levels do not exclude the disease. IgG4 positivity can also be observed in a range of other inflammatory conditions and some neoplasms, so IgG4 staining is not disease-specific.

Therefore, IgG4-positive staining is interpreted in the broader clinical context. The diagnosis of IgG4-related disease relies on a combination of clinical presentation, imaging findings, serology, and characteristic histopathology, of which IgG4 positivity is an important but not solitary component.