IgG2

Among human IgG subclasses, IgG2 ranks second in serum concentration and specializes in responses to encapsulated bacteria, being the dominant antibody raised against polysaccharide antigens such as the pneumococcal capsule. Compared with IgG1, its Fc region binds activating Fc gamma receptors and C1q weakly, and its shorter, more rigid hinge further limits effector recruitment, so IgG2 functions mainly through antigen neutralization and opsonic cooperation rather than direct cytolysis. Selective IgG2 deficiency is among the most common primary antibody deficiencies and predisposes to recurrent sinopulmonary infections, particularly in children. IgG2 is also a candidate Fc format when therapeutic antibodies must avoid effector activation.