Antibodies are proteins that are produced by B cells in response to an antigen. There are five main types of antibodies, which are classified by their structure and function: IgM, IgD, IgG, IgE and IgA. Antibodies perform several functions, including binding to antigens (both foreign invaders such as bacteria or viruses), opsonizing particles so that they may be attacked by phagocytes (immune cells) for destruction and neutralizing toxins produced by infectious agents. They also play a key role in the activation of complement proteins (when combined with the antigen), which aid in the destruction of invading microorganisms.
IgM is the first antibody that is produced in response to an antigen. It has a short half-life, which means it only lasts for a few days before it’s broken down and replaced by other antibodies.
IgD is a secreted antibody that is not present in the blood. IgD is found on the surface of B cells and it has no role in antigen binding. Instead, it acts as an important signaling molecule involved in cell signaling.
IgG is the most common antibody found in blood and extracellular fluid, allowing it to control infection at these locations. It can be found in both blood and extracellular fluid, as well as on mucosal surfaces such as the gastrointestinal tract. IgG is responsible for defense against parasites such as helminths. It also plays a role in immunity against viruses, fungi, protozoa and bacteria by virtue of its high avidity for antigens (foreign proteins).
IgE is responsible for defense against parasites such as helminths. However, IgE can also be responsible for allergic reactions. The role of IgE antibodies in allergic diseases is still unclear; however, it is clear that these antibodies can elicit the release of histamine from the mast cells in which they reside. In turn, this causes an inflammatory response (swelling and redness) at the site of an allergen contact with an individual's skin or mucous membranes.
The predominant immunoglobulin in the blood and secretions is IgA. It constitutes about 15% of total immunoglobulins in human serum and is found in high concentrations in many body fluids. For example, it has a concentration of 1 g/L in tears and saliva, 500 mg/L in breast milk, and up to 10 g/L in intestinal mucus (1).
The proteins that make up this particular type of antibody are secreted by plasma cells that reside within the lamina propria (the layer beneath epithelial cells) of mucosal surfaces throughout the body. In contrast to other types of antibodies that circulate through the bloodstream, IgA functions as an antigen-specific defense mechanism against viruses and bacteria entering through these surfaces into deeper tissues or organs such as lungs and kidneys.
IgE antibodies are able to elicit the release of histamine from the mast cells in which they reside. This process is called “mast cell degranulation.” Mast cells contain granules that store histamine and other inflammatory mediators, such as leukotrienes, prostaglandins and chemokines. Once activated by IgE, mast cells release these substances into tissues surrounding them; this causes inflammation and itching reactions at sites where allergens have entered the body (e.g., respiratory tract).
The ability of antibodies to bind to antigens varies at different body temperatures, with greater binding occurring at lower temperatures. This is why a fever can cause your immune system to be more effective. Antibodies do not actually spread a disease that is causing a fever, but they are able to attack and destroy the invading organism more effectively when your body temperature rises.
The immune system is a complex one, and the role of antibodies in it has been a topic of great interest since the 1960s. Antibodies are one of the main components within our immune system, and they work to protect us from foreign objects such as bacteria and viruses.
Antibodies are formed as part of an immune response when our bodies recognize a specific antigen (an invading organism). This can be done through either innate or adaptive immunity—meaning that there will be different types of antibodies with different functions depending on whether your body knows about the invader before its presence is detected by other parts of your body's defense system or if it detects it for the first time after being introduced into your bloodstream.
In conclusion, there are many types of antibodies and they play a very important role in our bodies. The IgM is the first antibody that is produced in response to an antigen. IgD gives the B cell a signal that it has successfully bound to an antigen. IgG is the most common antibody found in blood and extracellular fluid, allowing it to control infection at these locations. IgE is responsible for defense against parasites such as helminths.