Types of Antibodies and Their Functions

Isotypes refer to different classes or subclasses of antibodies based on their structural and functional properties. In humans, there are five main isotypes: IgG, IgM, IgA, IgE, and IgD. Each isotype has different function in the immune response which is discussed below:

IgG (Immunoglobulin G)

IgG is the main antibody in our blood, accounting for approximately 75% of all antibodies in the body. It has a strong ability to bind to bacteria and toxins.

Structure of IgG

IgG is a Y-shaped antibody composed of four protein chains – two heavy chains and two light chains. It has a molecular weight of about 150 kDa.

Function of IgG

• It plays a key role in providing long-term immunity against infections by recognizing and binding to specific antigens.
• IgG antibodies can neutralize toxins, opsonize pathogens for phagocytosis by immune cells, and activate the complement system to enhance immune responses.
• They also play a crucial role in memory immune responses. This enables the body to start a faster and stronger defense upon re-exposure to previously encountered antigens.
• It is unique because it can pass through the placenta, providing protection to newborns from the mother.

IgM (Immunoglobulin M)

It is produced first by B cells when pathogens invade, which plays a key role in the initial defense of the immune system.

Also Read: Difference Between T Cells And B Cells

Structure of IgM

• IgM is a pentameric antibody, meaning it consists of five antibody units linked together.
• Each unit contains two heavy chains and two light chains, forming a Y-shaped structure.

Function of IgM

• IgM is the first antibody produced by the immune system during an initial immune response to an antigen.
• It plays a crucial role in the primary immune response, helping to neutralize pathogens and activate other immune cells.
• IgM is efficient at agglutinating pathogens, making it easier for immune cells to recognize and eliminate them.
• Due to its large size and pentameric structure, IgM is not as effective at crossing tissues. So, they primarily stay in the bloodstream to fight systemic infections.

IgA (Immunoglobulin A)

IgA is present as monomers in the blood but forms dimers in secretions like bowel fluid, nasal discharge, and saliva.

Structure of IgA:

• IgA is a dimeric antibody, meaning it consists of two antibody units joined together by a structure called the J chain.
• Each antibody unit contains two antigen-binding sites, allowing IgA to bind to two antigens simultaneously.

Function of IgA:

• IgA plays a role in mucosal immunity, protecting mucous membranes in areas like the respiratory and genitourinary tracts.
• It acts as the first line of defense against pathogens by preventing them from attaching to mucosal surfaces and neutralizing toxins.
• IgA also helps to maintain the balance of healthy bacteria in the gut and other mucosal environments.
• IgA is also found in breast milk which protects newborn’s gastrointestinal tracts.

IgE (Immunoglobulin E)

IgE is originally related to immunity reactions to parasites. By binding to mast cells, it is involved in allergies such as hay fever.

Structure of IgE

• It is a type of antibody characterized by its Y-shaped structure, similar to other immunoglobulins.
• It consists of two heavy chains and two light chains connected by disulfide bonds, forming a specific binding site for antigens.

Function of IgE

• IgE has a role in allergic reactions by binding to allergens such as pollen, pet dander, or certain foods.
• Upon binding to allergens, IgE triggers the release of histamine and other inflammatory molecules from mast cells and basophils.
• This immune response leads to the typical symptoms of allergies, including itching, sneezing, runny nose, and swelling.
• IgE also plays a role in defense against parasites by activating eosinophils, a type of white blood cell that helps eliminate parasitic infections.

IgD (Immunoglobulin D)

IgD is present on the surface of B cells.

Structure of IgD

• It consists of two heavy chains and two light chains linked together in a Y-shaped structure.
• IgD antibodies are found on the surface of B cells, where they serve as antigen receptors.

Function of IgD

• The exact function of IgD is not fully understood.
• It is believed to play a role in the activation and regulation of B cells.
• IgD may be involved in the initiation of immune responses by helping B cells recognize and bind to antigens.
• Also, IgD may contribute to the maturation and differentiation of B cells into antibody-secreting plasma cells.
• It has a role in inducing antibody production and preventing respiratory tract infections.

Types of antibodies include IgA, IgD, IgE, IgG, and IgM. These various types of antibodies and functions help the immune system recognize and neutralize pathogens, toxins, and other foreign substances in the body. These antibodies protect against infections and diseases. In this article, we will cover the types of antibodies, their functions, and their structures in detail.