Antibodies: Definition, Structure, Types and Function

 

Antibodies:

The immune system produces protective proteins called antibodies. They attach to foreign substances, or antigens, such as bacteria, fungi, viruses, and toxins, and remove them from your body.

Where are the Antibodies Produced?

B cells—specialized white blood cells—produce antibodies. A B cell divides and clones when it comes into touch with an antigen. Millions of antibodies are released into your lymphatic and blood systems by these cloned B cells, also known as plasma cells.

Your body has antibodies in numerous places including your tears, saliva, lungs, skin, and even breast milk. Colostrum, a thick fluid generated by the breasts for a few days after giving birth, does, contain high concentrations of antibodies. Breastfeeding, or chestfeeding, helps strengthen your baby's immune system because of this.

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What is the Structured Antibody?

An antibody referred to as an immunoglobulin, is a Y-shaped molecule made up of two heavy and two light polypeptide chains. Antibody molecules' dual roles of mediating biological activity and binding to antigen are made possible by their structural makeup.

The fragment antigen-binding (Fab fragment) and fragment crystallizable regions (Fc region) of the antibody are responsible for each function.

An area of an antibody called a Fab fragment attaches itself to antigens. It consists of one domain for each of the heavy and light chains, one constant, and one variable. These domains mold the monomer's amino terminal end's paratope or antigen-binding site.

The tail portion of an antibody known as the Fc region interacts with certain complement system proteins as well as cell surface receptors known as Fc receptors. Antibodies can stimulate the immune system because of this characteristic. Immunoglobulin Gs' Fc regions have a highly conserved N-glycosylation site.

What Are the Five Different Antibody Types?

Five groups of antibodies are distinguished based on their constant region. The letters IgG, IgM, IgA, IgD, and IgE are used to represent the different classes of immunoglobulins. Antibody classes differ in terms of both activity and constant region. For instance, the most prevalent antibody, IgG, is mostly found in blood and tissue fluids, whereas IgA is found in the mucous membranes that line the gastrointestinal and respiratory systems.

 IgG Antibody Structure and Function:

The big globular proteins known as immunoglobulin G (IgG) antibodies are composed of four peptide chains and have a molecular weight of around 150 kDa. With two identical γ (gamma) heavy chains, each weighing approximately 50 kDa, and two identical light chains, each weighing approximately 25 kDa, it has a tetrameric quaternary structure.

Since IgG is produced months or even years after the antigen that caused it to do so is present, it offers long-term protection. IgG binds antigens, activates complement protein systems, neutralizes bacterial toxins, and provides protection against bacteria and viruses.

This antibody is the most prevalent one in your body, making up between 70% and 75% of all immunoglobulins. It is primarily present in tissue and blood fluids. IgG antibodies aid in defending your body against bacterial and viral infections.

IgM Antibody Structure and Function:

Antibodies known as immunoglobulin M (IgM) consist of five or six units, primarily pentamers but occasionally hexamers as well. These units are made up of two heavy chains (μ-chains) and two light chains, connected by disulfide bonds and a so-called J-chain.

The ABO blood group antigens on the surface of red blood cells are mediated by IgM. IgM improves phagocytosis-mediated cell ingestion.

IgM antibodies, which are present in your blood and lymph system, serve as your body's first line of defense against infections. They are also very important for immunological regulation.

IgA Antibody Structure and Function:

Antibodies with heavy (H) and light (L) chains are called immunoglobulin A (IgA). The constant region (Cα1, Cα2, Cα3), hinge region, and variable (V) region make up each H chain. The constituents Vκ or Vλ and CL make up light chains.

IgA's primary job is to attach to antigens on bacteria before they can infiltrate tissues. It combines the antigens and retains them in the secretions, allowing the antigen to be released along with the secretion. For mucosal surfaces like those of the lungs, nose, and intestines, IgA serves as the first line of defense.

IgA protects against eaten and inhaled microorganisms and is found in saliva, tears, mucus, breast milk, and intestinal fluid.

IgE Antibody Structure and Function:

Antibodies against immunoglobulin E (IgE) are unique to mammals. Plasma cells synthesize immunoglobulin E. IgE monomers are made up of two light chains and two heavy chains (ε chain), with the ε chain having four Ig-like constant domains (Cε1–Cε4).

IgE attaches itself to basophils and mast cells, which are involved in the immunological response. According to some scientists, the function of IgE is to inhibit parasites.

 Mast cells, a subset of white blood cells, release histamine and other chemicals into your bloodstream when exposed to IgE antibodies, which are primarily found in the skin, lungs, and mucous membranes. In the fight against allergic responses, IgE antibodies are useful.

 IgD Antibody Structure and Function:

Immature B-lymphocytes express immunoglobulin D (IgD) antibodies in their plasma membranes. Additionally, IgD is made and released; trace levels of this type can be detected in blood serum. The induction of antibody synthesis involves IgD.

Your B lymphocytes contain this antibody on their surface. Experts think that IgD promotes B cell maturation and activation, even though its precise function is unknown.

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The Production and Mechanism of An Antibody:

Macrophages intervene and collect foreign particles when an organism's immune system comes into contact with them, breaking them down and transferring them to B cells. When these antigens are exposed, B cells start to produce new antibodies that have a distinct paratope—the place where an antibody binds to an antigen—that will bind to an epitope—the part of the antigen that the antibody binds to. Every B cell lymphocyte produces a different antibody directed against a different epitope. After B cells have completed their programming, they release antibodies that bind with specific pathogens resulting in their elimination from our bodies.

This is accomplished by either having antibodies directly attack the pathogen (typically a virus) or, in the case of a bacteria, by attaching to the pathogen's surface and informing the immune system as a whole to eliminate the pathogen. These cells never leave the body and are always prepared to fight if they decide to re-enter it.