IgG

**Semantic type:** Amino Acid, Peptide, or Protein|Immunologic Factor

**Definition:** 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.

**Synonyms:** - Immunoglobulin G