New understanding of Mikulicz's disease/IgG4-related disease and Sjögren's syndrome

IgG4-related disease (IgG4-RD) is a systemic disease characterized by the elevation of serum IgG4 and infiltration of IgG4-positive plasma cells in the target organs, and its molecular mechanism of pathogenesis remains to be clarified. IgG4-related dacryoadenitis and sialoadenitis (IgG4-DS), so-called Mikulicz's disease or Küttner's tumor, is included in IgG4-RD and shows clinical and histological similarities to Sjögren's syndrome (SS). In this review, we focus on the selective localization and respective functions of Th cell subsets and discuss the differences between IgG4-DS and SS to clarify the clinical and pathogenic mechanisms of these diseases.