serum immunoglobulin G subclass level serum immunoglobulin G2a level 2014-01-27T14:57:50Z CMO:0002116 The amount in a specified sample of serum of the G2a subclass of immunoglobulin G (IgG), the most abundant class of antibodies found in blood serum and lymph. IgG antibodies are active against bacteria, fungi, viruses, and foreign particles, and trigger action of the complement system. IgG subclasses differ in the structure of their hinge regions. IgG2a is able to activate complement and bind to the Fc receptor on phagocytic cells. clinical_measurement_ontology jsmith serum IgG2a level