IgG4 is an immunoglobulin G subclass of antibody. Mouse monoclonal IgG4 [HP6025] is specific for the Fc region of human IgG4. IgG4 can be helpful in the diagnosis of IgG4 related systemic disease (IgG4-RSD). IgG4-RSD, also known as IgG4-related sclerosing disease, can be found in many different organs and presents itself with such symptoms as lymphoplasmacytic infiltration, mass formation, sclerosis, obliterative phlebitis and increased expression of IgG4+ plasma cells as well as a high IgG4+/IgG+ ratio, typically >30% (1-4).
IgG4 has been shown to be overexpressed in inflammatory pseudotumor (IPT) and under expressed in inflammatory myofibroblastic tumor (IMT). IgG4 may be a useful differential marker in a panel with IgG (IgG4+/ IgG+ plasma cell ratio is higher in IPT) and ALK (positive in IMT) (4,5).
In pulmonary nodular lymphoid hyperplasia (PNLH), there are an increased number of IgG4+ plasma cells as well as a higher ratio of IgG4+ to IgG+ plasma cells as compared to other pulmonary lymphoid proliferations. These characteristics may aid in distinguishing PNLH from low-grade B-cell lymphoma of the bronchus-associated lymphoid tissue (BALT) (6).