Immunology and Serology Topic: Antibody
Definition of Antibody
The definition of an antibody is “an immunoglobulin capable of specific combination with the antigen that caused its production in a susceptible animal.” Antibodies are produced in the body in response to the invasion of foreign molecules. An antibody, abbreviated as Ab, is also known as an immunoglobulin, or Ig. Human immunoglobulins are a class of glycoproteins that confer humoral immunity and are structurally and functionally similar (82-96 percent protein and 4-18 percent carbohydrate).
Antibodies typically are proteins that protect your body when an unwelcome substance enters it. Antibodies, which are produced by your immune system, bind to these unwanted substances and eliminate them from your system.
Electrophoresis separation can be used to isolate many antibodies from the gamma globulin fraction of protein. However, because not all antibodies have gamma electrophoresis mobility, the term immunoglobulin has replaced gamma globulin. Antibodies can be found in blood plasma or serum, as well as tears, saliva, and colostrums.
An antibody’s primary function in the body’s defenses is to bind to antigen, which may be enough to neutralize bacterial toxins or some viruses. Larger antigens, such as bacteria, usually necessitate a secondary interaction of an antibody molecule with another effector agent, such as complement.
Complete antibodies and incomplete antibodies are the two types of antibodies.
- Complete antibodies are heat-resistant antibodies that, when combined with their specific antigen, produce a different immunologic response. These antibodies can cross the transplacental barrier.
- Incomplete antibodies, also known as blocking antibodies, are heat labile substances that do not elicit an immune response when they bind to an antigen.
Incomplete antibodies cannot pass through the placental barrier.
Antibodies are typically described in terms of how they react to antigen. These include:
- Antitoxin antibodies, which neutralize toxins or toxoids.
-Agglutinin – antibodies that immobilize motile bacteria before aggregating cells into clumps.
Precipitins are antibodies that form complexes with soluble antigens, resulting in precipitates.
Lysine – antibodies that, in conjunction with complement, dissolve antigenic cells.
-Opsonins are antibodies that bind to surface components of microbial and other cells, allowing them to be phagocytized more easily.
Immunoglobulins are composed of a polypeptide chain that is held together by a disulphide bond. Each molecule is made up of one heavy (long) chain and one light (short) chain.
The heavy (H) chain is approximately twice the size of the light (L) chain. As a result, an immunoglobulin monomer molecule is made up of four polypeptide chains: two identical H and L chains. Every immunoglobulin has the same number of heavy and light chains and is represented by the general formula (H2L2) n.
In any single immunoglobulin protein, all of the light and heavy chains are identical. This variability is largely confined to the N-terminus in both heavy and light chains, while the sequence of the other domains remains relatively constant.
In any single immunoglobulin protein, all of the light and heavy chains are identical. This variability is largely confined to the N-terminus in both heavy and light chains, while the sequence of the other domains remains relatively constant. As a result, the N-terminus of a heavy or light chain polypeptide is referred to as the variable region VH or VL. The other domains are known as the constant regions CH and CL.
Light chain polypeptides have a single CL domain, whereas heavy chain CH regions have three or more domains that are numbered sequentially (CH1, CH2, —, etc.), beginning with the domain closest to the VH. When viewed schematically, the protein has a T or Y shaped configuration. In most immunoglobulins, the hinge region is located at the base of each arm in the T or Y and is located between the CH and CH2 domains. The hinge region provides flexibility, allowing the two arms to move relatively freely in relation to one another.
Immunoglobulin is another term for antibody.
Also read: Immunology and Serology Topic: Immunity
Five different types of antibodies and their functions
Antibodies are classified into five types based on their location. Each is identified by a letter that is followed by an abbreviation of the term “immunoglobulin” (Ig):
- IgA, which is found in saliva, tears, mucus, breast milk, and intestinal fluid, protects against pathogens that are ingested or inhaled.
- Consists of 2 subunits with 4 antigen binding sites.
- This antibody can be found on the surface of B cells. Though its precise function is unknown, experts believe IgD aids in B cell maturation and activation.
- Has short half life in serum.
- IgE antibodies, which are found primarily in the skin, lungs, and mucus membranes, cause mast cells (a type of white blood cell) to release histamine and other chemicals into the bloodstream.
- IgE antibodies aid in the prevention of allergic reactions.
- This is the most common antibody, accounting for roughly 70% to 75% of all immunoglobulins in your body. It is mostly found in blood and tissue fluids.
- IgG antibodies aid in the defense of the body against viral and bacterial infections.
- IgM antibodies, which are found in your blood and lymph system, serve as your body’s first line of defense against infections.
- They are also important in immune regulation.