A molecular model of immunoglobulin G1 (IgG1), a monoclonal antibody secreted by plasma B cells in the immune system. IgG controls infections taking place in body tissues, and is the main antibody isotype found in the blood and extracellular fluid. IgG antibodies can bind to pathogen surfaces to allow phagocytic immune cells to recognize and ingest the invading pathogen, as well as neutralize toxins.