Immunoglobulin

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Immunoglobulins are proteins formed from B-cells that target a specific antigen (or more accurately epitope) and form the basis of the body's humoral immune response.

The basic structure of an immunoglobulin consists of two heavy chain (forming the Fc component - fraction crystallisable region or fraction constant region) and two light chains, the latter either kappa or lambda (forming the Fab - fraction antibody binding). The light chains are the component that results in the configuration recognising specific antigen-binding.

There are 5 sub-classes: IgG, IgA, IgM, IgE and IgD. Some are further sub-typed (e.g. IgG1 to IgG4 and IgA1/2).

When the immune system works normally, short-lived plasma cells produce antibodies that eliminate microbial infections. Re-exposure to antigens activates memory B-cells which are able to ramp up production of antibodies quickly, forming the basis for lasting immunity.

An increase in the amount of immunoglobulin may be normal in the face of an infection, but can be pathological in certain circumstances. An over-production of a single type of antibody, as identified by its heavy chain and light chain, is typically due to expansion of a single monoclonal neoplastic (i.e. myeloma) or pre-neoplastic cell. Rarely, more than one clone can be involved (oligoclonal).

A decrease in immunoglobulin may be due to a range of conditions - see hypogammaglobinaemia.

Contents

Clinical uses

Immunoglobulin has a wide range of specific and general immunomodulating effects. Immunoglobulin isolated from those who have recovered from an infection is likely to be active against that infection. Pooled human immunoglobulin will help minimise infection of any cause in those with hypogammaglobinaemia. The immunomodulating actions of pooled human immunoglobulin can be useful in autoimmune disease where an individuals immune system can be modulated to therapeutic benefit. All use is a balance between potential clinical benefit, potential risk, alternative therapies and the resource cost of a relatively expensive blood product.

Blood Product

Immunoglobulin (commonly referred to as "human normal immunoglobulin" or "HNIG") is occasionally used to protect vulnerable individuals (by providing "passive immunity") against certain infectious diseases. In England, immunoglobulin can be obtained from or via the Health Protection Agency - see their Immunoglobulin Handbook page.

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There is an immunoglobulin demand management scheme with details at http://www.igd.nhs.uk/ which requires clinicians to use the products for approved indications, notify use in a national database, and provide outcome data - mostly applicable for intravenous human normal immunoglobulin (IVIg)as other products are indication specific

Therapeutic Immunoglobulins

Normal immunoglobulin

Human normal immunoglobulin (HNIG) is prepared from pooled donations and may be used to protect susceptible contacts against common viruses such as hepatitis A, measles, mumps and rarely rubella. Intravenous immunoglobulin (IVIG) can be useful in treating autoimmune associated disease processes. This indication has resulted in steady increases in world wide demand. There is the potential for biological contamination or as with Octagam® in 2010 where thromboembolic reactions occurred, unexpected events probably related to processing affecting other plasma proteins.


Hepatitis B immunoglobulin

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HBIG is used to protect an individual exposed to the Hepatitis B.

Rabies immunoglobulin

Usually administered around the cleaned wound followed by vaccination.

Snake envenomation

Anti-sera exists but is likely to easily obtainable only for endemic species.

Tetanus immunoglobulin

Antibodies against the tetanus toxoid prevents tetanus in patients not previously innoculated against tetanus toxoid or have developed frank tetanus.

Anti-D(Rh0) immunoglobulin (Rhesus D immunoglobulin)

Designed to target Rhesus D positive erythrocytes than may be transferred from a baby to its Rhesus negative mother during pregnancy. The Anti-D immunoglobulin targets and neutralises the Rhesus D antigen. This prevents the mother's immune system from encountering the antigen and protects any further Rhesus positive babies that the mother may have.

Varicella-Zoster immunoglobulin

Cytomegalovirus immunoglobulin

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