Five Classes [subclasses] of Immunoglobulins

  • Immunoglobulin G (IgG) [subclass IgG1, IgG2, IgG3, IgG4]
  • Immunoglobulin A (IgA) [subclass IgA1, IgA2]
  • Immunoglobulin M (IgM)
  • Immunoglobulin D (IgD)
  • Immunoglobulin E (IgE)
Image: Drawings of Immunoglobulin molecules.
Image: Drawing of immunoglobulin molecules attacking bacteria cell.

The five classes [subclasses] of immunoglobulins include:

IgG
Image: Drawing of a fetus within a representative 70-75% total immunoglobulin pool.

Immunoglobulin G is the main immunoglobulin present in the blood and represents 70% to 75% of the total immunoglobulin pool. Several forms (subclasses) of IgG cross the placental barrier and are responsible for defense against infection in the first few months of a baby's life.

IgA
Image: Immunoglobulin A (secretory).

Immunoglobulin A provides localized antibody protection on mucosal surfaces. It is found in mucosal secretions such as saliva, tears, sweat, nasal fluids, fluids of the lung and colostrum, genito-urinary tract, and gastro-intestinal tract. It is a primary defense against microorganisms attacking exposed mucosal surfaces. IgA functions by preventing the microorganism from adhering to, and penetrating, the mucosal epithelial lining.

IgM
Image: Immunoglobulin M

Immunoglobulin M is the major immunoglobulin present on the surface of immature B cells and is effective against microbes by binding with complement and causing agglutination and bacteriolysis. It is the first immunoglobulin to take part in the immune response and plays an important role in controlling bacteria that find their way into the blood stream (bacteremia).

IgD
Image: Immunoglobulin D with a B-cell.

Immunoglobulin D is a trace antibody in the serum and is present on the surface of B cells. It may be involved in stimulating and suppressing these antibody producing cells in the manufacture of antibodies.

IgE
Image: Immunoglobulin E.

Immunoglobulin E is found in very low concentration in human serum, but it increases during allergic reactions and some parasitic infections. IgE is bound to high affinity membrane receptors (FceRI) on mast cells in the tissue and basophils in the blood. Cross-linking of cell bound IgE by an allergen elicits the release of inflammatory mediators like histamine and several cytokines. IgE is also the main immunoglobulin responding to infection caused by certain parasites.

Before we examine how these immunoglobulins function during inflammation and periodontal destruction, let's review the key cellular elements of the immune system, most of which are blood components. When an organism invades the body, the body's initial response is carried out by white blood cells.

Image: Artistic drawing of cells.