Immunoglobulin G

Shortened to IgG

IgG

IgG - B. Catchpole, RVC 2008

IgG is the major antibody in blood plasma and constitutes at least 80% of all antibody in the body. It is the smallest immunoglobulin so it can readily leave the blood plasma and enter tissues.

Structure

IgG is Y-shaped with three constant regions and a heavy chain subunit type γ. There are several different IgG subclasses depending on the species coded for by the IGHG gene.

• Ruminants have three subclasses
  • G1-G3
  • IgG1 is the major antibody in ruminant mucosal secretions and colostrum
• Dogs, rodents (and cats?) have four subclasses
  • Dogs: G1-G4
  • Rodents: G1-G3 (G2a, G2b)
• Pigs have five subclasses
  • G1-G4 (G2a, G2b)
• Horses have six subclasses
  • G1-G6

Production

IgG is produced by plasma cells in the spleen, bone marrow and lymph nodes.

Function

• Some IgG subclasses can activate complement via the classical pathway
• Some subclasses act as targets for macrophages, eosinophils and neutrophils
  • It is therefore the major antibody in tissue fluids and lymph
• IgG specifically binds to antigens on bacteria
  • Causing agglutination and opsonisation

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^{Immunoglobulins: Immunoglobulin A, Immunoglobulin D, Immunoglobulin E, Immunoglobulin G & Immunoglobulin M}