IgG1

IgG1 is a subclass of immunoglobulin G, one of the four human IgG subclasses. It is the most abundant IgG in serum, typically accounting for about 60–70% of total IgG. IgG1 is produced by plasma cells, especially during secondary immune responses, and it provides defense against protein antigens and viral infections.

Structurally, IgG1 consists of two identical gamma-1 heavy chains and two light chains. The molecule has a hinge region of moderate length and an Fc domain that is glycosylated at asparagine 297. This Fc glycosylation modulates interactions with Fc receptors and complement proteins and influences effector functions and half-life.

IgG1 efficiently engages Fc gamma receptors on various immune cells, including high-affinity FcγRI (CD64) and FcγRIII (CD16) on NK cells and macrophages. Through these interactions, IgG1 can mediate antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis. IgG1 can also activate the classical complement pathway by binding C1q, though its capacity is generally surpassed by IgG3 in complement activation.

IgG1 crosses the placenta via the neonatal Fc receptor (FcRn), contributing to passive fetal and neonatal immunity. It has a relatively long serum half-life, around 21 days, due to FcRn-mediated recycling.

In clinical and therapeutic contexts, IgG1 is a common isotype for monoclonal antibodies and antibody-based therapies because of its potent effector functions. Fc engineering can tailor IgG1 antibodies to enhance or reduce ADCC or complement activation, depending on therapeutic needs.