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Immunoglobulins

Immunoglobulins, also known as antibodies, are proteins produced by B cells of the immune system in response to the presence of foreign substances called antigens. They play a crucial role in the adaptive immune response by recognizing and binding to specific antigens, thereby facilitating their neutralization and elimination from the body.

Immunoglobulins are Y-shaped molecules composed of four polypeptide chains: two heavy chains and two light chains as shown in the diagram below.

There are five major classes of immunoglobulins:

1. IgG (Immunoglobulin G):

• IgG is the most abundant class of immunoglobulins in the bloodstream and tissues.
• It provides long-term protection and is involved in the defense against bacteria, viruses, and toxins.
• IgG can cross the placenta, providing passive immunity to the developing fetus.

2. IgM (Immunoglobulin M):

• IgM is the first antibody produced during an initial immune response.
• It is involved in the early stages of an infection and activates the complement system, promoting the elimination of pathogens.
• IgM is found mainly in the bloodstream and exists as a pentamer (five units) structure.

3. IgA (Immunoglobulin A):

• IgA is primarily found in mucosal areas, such as the respiratory and gastrointestinal tracts.
• It plays a crucial role in defense against pathogens at mucosal surfaces, preventing their entry into the body.
• IgA is also present in secretions like tears, saliva, breast milk, and mucous.

4. IgE (Immunoglobulin E):

• IgE is involved in allergic and hypersensitivity reactions.
• It triggers the release of chemical mediators, such as histamine, in response to allergens.
• IgE is associated with allergic conditions like asthma, hay fever, and hives.

4. IgD (Immunoglobulin D):

• IgD is found on the surface of B cells and is involved in their activation.
• Its precise role is not fully understood, but it likely participates in the regulation of the immune response.

Each immunoglobulin class has different functions and roles in the immune response. They can bind to antigens with high specificity due to their variable regions, allowing for recognition of a wide range of pathogens and foreign substances. Additionally, immunoglobulins can activate other components of the immune system, such as complement proteins, to enhance the elimination of pathogens.

The production and secretion of immunoglobulins are tightly regulated by various immune cells and signaling molecules. Deficiencies or abnormalities in immunoglobulin production can lead to immunodeficiency disorders, making individuals more susceptible to infections.