Immunoglobulin G Subclass 4 Unit Converter

Immunoglobulin G Subclass 4 (IgG4) is the least abundant of the four IgG subclasses in human blood. It typically makes up only about 1-4% of total serum IgG, compared with IgG1 at 60-70%, IgG2 at 20-30%, and IgG3 at 5-8%.

IgG4 has a unique molecular property called Fab-arm exchange, where its two halves can recombine with halves from other IgG4 molecules. This makes most circulating IgG4 functionally monovalent, meaning each molecule can only bind one antigen at a time rather than cross-linking antigens together.

Because of this structure, IgG4 has reduced ability to activate complement or trigger inflammatory immune responses, giving it a fundamentally anti-inflammatory character. It plays a key role in immune tolerance and modulating allergic responses.

IgG4 is produced by plasma cells, which are fully differentiated B lymphocytes found in lymph nodes, spleen, and mucosal-associated lymphoid tissues. The switch to IgG4 production is driven primarily by the cytokines IL-4, IL-13, and IL-10 from T helper 2 cells and regulatory T cells, and develops slowly through chronic or repeated antigen exposure rather than acute infections.