major immunoglobulin in normal human serum, distributed evenly between the intravascular and extravascular pools; it is the major antibody of secondary immune responses and the exclusive antitoxin class.
The major immunoglobulin isotype class in normal human serum. There are several isotype subclasses of IgG, for example, IgG1, IgG2A, and IgG2B.
An immunoglobulin isotype (subclass) that characterizes secondary immune responses. This isotype is further broken down into several smaller subclasses (IgG1, IgG2a, IgG2b, IgG3 in the mouse; IgG1-4 in the human), and each subclass is differentially synthesized and secreted into the serum upon differential immune stimuli.