A spectrum of systemic autoimmune diseases in which immunoglobulin g4 plays a pathophysiologic role. it can affect multiple organs in highly variable presentations, characterized by inflammatory lesions composed of igg4-positive plasma cells, further infiltrated by t helper cells (t-lymphocytes, helper-inducer) when linked to progressive fibrosis and eventual organ damage.

IgG4-related disease (IgG4-RD), formerly known as IgG4-related systemic disease, is a chronic inflammatory condition characterized by tissue infiltration with lymphocytes and IgG4-secreting plasma cells, various degrees of fibrosis (scarring) and a usually prompt response to oral steroids. In approximately 51–70% of people with this disease, serum IgG4 concentrations are elevated during an acute phase. It is a relapsing-remitting disease associated with a tendency to mass forming, tissue-destructive lesions in multiple sites, with a characteristic histopathological appearance in whichever site is involved...