What are Antibody?
Antibody, or immunoglobulins (Ig), are Y-shaped proteins produced by the immune system to detect and neutralize harmful invaders like viruses, bacteria, and toxins, which are called antigens. Each antibody is specific to a particular antigen, fitting with it like a key fits into a lock. This process helps the immune system eliminate the threat.
Table of Contents
Antibodies play a critical role in protecting the body from infections and diseases.
Structure of Antibodies
An antibody consists of four protein chains: two heavy chains and two light chains, connected by disulfide bonds to form a Y-shape. Each chain is divided into two regions:
Constant Region: This section is the same across antibodies of the same class and is responsible for initiating the immune response once an antigen has been identified.
Variable Region: This part varies from antibody to antibody and is responsible for binding to a specific antigen. Located at the tips of the Y structure, the variable region is what allows antibodies to recognize and attach to diverse antigens.
At the very end of the variable region is the antigen-binding site, which interacts directly with the antigen. The shape of this site determines which antigen the antibody can bind to.
Types of Antibodies
There are five main classes of antibodies, each with unique roles and structures. These classes are:
IgG
Structure: Monomer (one Y-shaped unit)
Location: Found in blood and other bodily fluids
Function: The most abundant antibody, IgG provides long-term protection after infection or vaccination. It can also cross the placenta to provide immunity to a fetus.
IgM
Structure: Pentamer (five Y-shaped units linked together)
Location: Present in blood and lymph fluid
Function: IgM is the first antibody produced during an immune response and is effective at clumping antigens together (agglutination) to make them easier for immune cells to remove.
IgA
Structure: Dimer (two Y-shaped units)
Location: Found in mucous membranes of the respiratory and digestive tracts, and in secretions like saliva, tears, and breast milk.
Function: IgA protects mucosal surfaces from infection and, in breast milk, provides immune protection to infants.
IgE
Structure: Monomer
Location: Found in the lungs, skin, and mucous membranes
Function: IgE plays a key role in allergic reactions. When it binds to allergens, it triggers immune cells to release chemicals like histamine, causing allergy symptoms. It also helps fight off parasitic infections.
IgD
Structure: Monomer
Location: Found on the surface of immature B cells
Function: IgD is involved in starting the immune response but its precise role is not fully understood compared to other antibody types.
Roles of Antibodies
Antibodies perform several critical functions in the immune response:
Neutralization
Antibodies can block pathogens from entering cells or neutralize toxins, preventing them from causing harm.
Opsonization
By coating pathogens, antibodies mark them for destruction by immune cells like macrophages, making it easier for these cells to recognize and engulf the invader.
Agglutination
Antibodies can bind multiple antigens simultaneously, causing them to clump together. This makes it easier for immune cells to capture and eliminate the pathogens.
Complement Activation
Antibodies can trigger the complement system, a series of proteins in the blood that help destroy pathogens. When activated, the complement system can form pores in a pathogen’s membrane, leading to its destruction.
Antibody-Dependent Cellular Cytotoxicity (ADCC)
Antibodies attach to infected or abnormal cells (like cancer cells), which are then targeted by immune cells like natural killer cells that release toxic substances to kill the damaged cells.
Antibodies in Medicine
Antibodies are widely used in medical applications. They are essential in diagnostic tests, such as pregnancy tests or tests for diseases like COVID-19, to detect specific antigens. Additionally, monoclonal antibodies (lab-made antibodies) are used as treatments for conditions such as cancer, autoimmune diseases, and infections, by targeting specific cells or proteins involved in these illnesses.
Conclusion
Antibodies are essential components of the immune system, acting as highly specialized defenders that recognize and neutralize harmful invaders. Their unique structure allows for precise targeting of antigens, and the different classes of antibodies perform specialized roles in protecting the body. Beyond their natural function, antibodies have significant applications in modern medicine, providing both diagnostic tools and therapies for a wide range of conditions.
Frequently Asked Questions (FAQ)
What is the name of the virus that cause COVID-19 ?
COVID-19, caused by the SARS-CoV-2 virus, is a respiratory disease that emerged in late 2019 in Wuhan, China.
What do you mean by Agglutination ?
Agglutination is a process in which particles, such as bacteria or red blood cells, clump together due to the binding action of specific antibodies.
Related Articles
