immunoglobulin g is the most abundant antibody class in the human body, comprising about 75% of all serum antibodies. it is a vital glycoprotein produced by b cells and plays a central role in the adaptive immune system. igg is responsible for identifying and neutralizing bacteria, viruses, and toxins. it can cross the placenta, providing passive immunity to newborns.
chemical properties
- molecular weight: ~150 kDa
- structure: Y-shaped molecule with two antigen-binding (fab) regions and one fc region
- glycosylation: n-linked glycan on the fc region affects immune activity
- half-life in serum: ~21 days
- subclasses: igg1, igg2, igg3, igg4 — each with specialized functions
usefulness in medicine
- igg provides long-term protection following infection or vaccination.
- it is used in passive immunotherapy to treat infections, autoimmune diseases, and immunodeficiencies.
- intravenous immunoglobulin (IVIG) is a therapeutic preparation of pooled igg from healthy donors.
- low igg levels (hypogammaglobulinemia) can lead to recurrent infections.
- elevated igg may indicate chronic inflammation, autoimmune disease, or multiple myeloma.
antibacterial and antimicrobial activity
- igg binds to pathogen antigens, marking them for phagocytosis and activating the complement system.
- it neutralizes bacterial toxins and prevents virus entry into host cells.
- igg plays a key role in antibody-dependent cellular cytotoxicity (ADCC), aiding in the destruction of infected or abnormal cells.
- research highlights: