Immunoglobulins (Ig)

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Original Editor - Lucinda hampton

Top Contributors - Kirsten Coutts, Lucinda hampton, Kim Jackson and Nupur Smit Shah  

Introduction

Immunoglobulins (Ig) or Antibodies: Glycoproteins that your immune cells make to fight off bacteria, viruses, fungi, parasites, cellular antigens, chemicals, and synthetic substances.

• Are produced by plasma cells.
• B cells are instructed by specific immunogens, for, example, bacterial proteins, to differentiate into plasma cells, which are protein-making cells that participate in humoral immune responses.
• Immunoglobulins constitute about 20% of the protein in plasma
• They act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses, and aiding in their destruction.
• The antibody immune response is highly complex and exceedingly specific.
• Antibody tests are used to detect disease-specific antibodies in a blood sample..
• WHO officially coined termed the term Immunoglobulins for antibodies in 1964.

5 types of immunoglobulins in humans

There are five main types of immunoglobulins, each immunoglobulin can have a different binding site that matches a specific antigen. The body can produce an infinite number of binding sites to bind to antigens.

Immunoglobulin G (IgG)

• Accounts for around 75% of all antibodies in the human body.
• Depending on the antigen, IgG can either tag a pathogen so other immune cells and proteins will recognize it, or it can promote the release of toxins to directly destroy the microorganism.
• IgG can sometimes trigger an undesirable response in people with autoimmune disorders.

Immunoglobulin A (IgA)

• Accounts for 15% of all antibodies in the human body
• Primarily found in mucosal tissues (eg mouth, vagina, and intestines) as well as in saliva, tears, and breast milk.
• Produced by B cells and secreted from the lamina propria (a thin layer within mucosal tissues).
• One of the body's first-line defenses against infection - it binds to pathogens tagging them for destruction and preventing them from sticking to the epithelium (which lines the body's tissues).
• Associated with hypersensitive reactions in people with celiac disease and several other autoimmune disorders.

Immunoglobulin A (IgM)

• Immunoglobulin M (IgM) is also one of the first antibodies recruited by the immune system to fight infection.
• IgM populations rise very quickly when the body is first confronted with an infectious organism, and then they plummet as IgG antibodies take over.
• IgM is also produced by B cells and, when bound to a pathogen, will spur other antibodies and immune cells into action.
• A subset of IgM helps B cells "remember" a pathogen after it has been destroyed. If you were to become re-exposed to the pathogen later, your immune system should respond more quickly due to your memory B cells.

Immunoglobulin E (IgE)

• The antibody responsible for the allergic response that is mostly found in the lungs, skin, and mucosal membranes.
• Produced by B cells secreted by lymph nodes or other lymphoid tissues situated near the site of the allergen.
• When IgE binds to an allergen, it triggers a cascade of events. Basophils and mast cells (subtypes of WBCs,) degranulate and release histamine, an inflammatory compound, into the bloodstream.
• IgE also helps to protect the body from parasitic infections, including helminths (parasitic worms).

Immunoglobulin D (IgD)

• Accounts for only around 0.25% of antibodies in the human body.
• Important in the early stages of the immune response.
• Unlike other antibodies, it does not actively circulate but binds to B cells to instigate the immune response. As a signaling antibody,
• IgD helps incite the release of front-line IgM to fight disease and infection.
• The least understood antibody, with little known about how it might participate in other parts of the immune system

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