Increased Immunoglobulin G4-positive Plasma Cells in Lymphadenoma of the Salivary Gland: An Immunohistochemical Comparison Among Lymphoepithelial Lesions.

Background: Lymphadenoma (LA) of the salivary gland, nonsebaceous type, is an uncommon benign lymphoepithelial neoplasm. The histogenesis of the lymphoid component of LA is under debate as in Warthin's tumor. A recent study has described immunoglobulin (Ig) class switching to IgG4 in a subset of Warthin's tumors. The aim of this study is to evaluate IgG4 status of LA and presume the role of IgG4 status in pathogenesis of LA.

Materials and methods: The distribution of IgG-positive and IgG4-positive cells was compared by immunohistochemistry among 15 lymphoepithelial lesions of the salivary gland (8 LAs, 3 lymphoepithelial carcinomas, and 4 lymphoepithelial cysts). Epstein-Barr virus in situ hybridization was also performed.

Results: IgG-positive and IgG4-positive plasma cells were observed in all cases, but to a remarkable degree (IgG4>100/hpf) in 2 of 8 LAs. The IgG4 plasma cells in LA were distributed in interfollicular areas and in the vicinity of epithelial nests. Among all cases, the mean number of IgG4 plasma cells was not correlated with the presence of germinal centers (12/15) or Epstein-Barr virus positivity (2/15).

Conclusions: Increased IgG4 plasma cells in LA suggest involvement of an immune reaction in the pathogenesis of LA similar to Warthin's tumor.