Show pageBacklinksCite current pageExport to PDFBack to top This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong. ====== Immunoglobulin G4 (IgG4) ====== Immunoglobulin G4 (IgG4) is one of the four subclasses of immunoglobulin G (IgG), representing less than 5% of total serum IgG in healthy individuals. It plays a unique role in immune regulation and is notably implicated in IgG4-related disease (IgG4-RD). ===== Basic Properties ===== * Molecular weight: ~150 kDa * Serum concentration: 0.05–1.5 g/L * Comprises <5% of total IgG * Half-life: ~21 days * Poorly activates complement via the classical pathway ===== Structural Characteristics ===== * Fab-arm exchange: IgG4 molecules can exchange half-molecules, leading to functionally monovalent antibodies * Low affinity for Fc receptors and C1q → reduced pro-inflammatory activity ===== Functional Role ===== * Generally considered anti-inflammatory * Acts as a "blocking antibody" in allergy desensitization therapy * May downregulate immune responses by competing with other IgG subclasses ===== Clinical Relevance ===== ==== ↑ Elevated IgG4 levels observed in: ==== * IgG4-related disease (IgG4-RD) * Atopic dermatitis * Parasitic infections * Certain cancers (e.g., pancreatic) * Chronic inflammatory diseases (non-specific) ==== ↓ Low IgG4 levels: ==== * Often not clinically significant unless associated with other immunoglobulin deficiencies ===== Measurement ===== * Serum IgG4 quantification by nephelometry or ELISA * Used in diagnosis and monitoring of IgG4-RD, but not diagnostic alone ===== In IgG4-Related Disease (IgG4-RD) ===== * Elevated serum IgG4 in ~60–70% of cases * Tissue infiltration with IgG4+ plasma cells is key for diagnosis * Not all patients with elevated IgG4 have IgG4-RD, and vice versa ===== Differential Diagnosis for Elevated IgG4 ===== * [[Immunoglobulin G4-related disease]] * Allergic diseases * Parasitic infections * Multicentric Castleman disease * Autoimmune pancreatitis * Chronic sinusitis immunoglobulin_g4.txt Last modified: 2025/06/11 07:05by administrador