Types Of Antibodies And Their Functions

Antibodies can be divided into five classes—IgM, IgG, IgA, IgD, IgE—based on their physicochemical, structural, and immunological properties.

Types Of Antibodies And Their Functions
Types Of Antibodies And Their Functions

Define Antibody? Explain its Classes and their biological Activities?

Ans: Antibody (Ab) also know as Immunoglobulin (Ig) is the large Y-shaped protein produced by the body’s immune system when it detects harmful substances, called antigens like bacteria and viruses.

The production of antibodies is a major function of the immune system and is carried out by a type of white blood cell called a B cell (B lymphocyte), differentiated B cells called plasma cells. The produced antibodies bind to specific antigens express in external factors and cancer cells.

Antibody Classes and their biological Activities
Types Of Antibodies And Their Functions

Structure of Antibody

Antibodies are heavy (~150 kDa) globular plasma proteins. The basic structure of all antibodies is the same

Antibody Classes and their biological Activities
Types Of Antibodies And Their Functions

Structure of Antibody

There are four polypeptide chains: two identical heavy chains and two identical light chains connected by disulfide bonds. Light Chain (L) consists of polypeptides of about 22,000 Da and Heavy Chain (H) consists of larger polypeptides of around 50,000 Da or more.

There are five types of Ig heavy chain (in mammal) denoted by the Greek letters: α, δ, ε, γ, and μ. There are two types of Ig light chains (in mammals), which are called lambda (λ) and kappa (κ).

An antibody is made up of a variable region and a constant region, and the region that changes to various structures depending on differences in antigens is called the variable region, and the region that has a constant structure is called the constant region.

Antibody Classes and their biological Activities
Types Of Antibodies And Their Functions

Structure of Antibody

Each heavy and light chain in an immunoglobulin molecule contains an amino-terminal variable (V) region that consists of 100 to 110 amino acids and differs from one antibody to another. The remainder of each chain in the molecule – the constant (C) region exhibits limited variation that defines the two light chain subtypes and the five heavy chain subclasses.

Some heavy chains (α, δ, γ) also contain a proline-rich hinge region. The amino terminal portions, corresponding to the V regions, bind to antigen; effector functions are mediated by the carboxy-terminal domains. The ε and μ heavy chains, which lack a hinge region, contain an additional domain in the middle of the molecule. CHO denotes a carbohydrate group linked to the heavy chain.

Also, Check Helpful Notes Paper 

Types Of Antibodies And Their Functions

A serum containing antigen-specific antibodies is called antiserum. The 5 types – IgG, IgM, IgA, IgD, IgE – (isotypes) are classified according to the type of heavy chain constant region and are distributed and function differently in the body.

Types of Antibody

What Are The Five (5) Different Types Of Antibodies And Their Functions


IgG is the most abundant antibody isotype in the blood (plasma), accounting for 70-75% of human immunoglobulins (antibodies). IgG detoxifies harmful substances and is important in the recognition of antigen-antibody complexes by leukocytes and macrophages. IgG is transferred to the fetus through the placenta and protects the infant until its own immune system is functional.

IgM usually circulates in the blood, accounting for about 10% of human immunoglobulins. IgM has a pentameric structure in which five basic Y-shaped molecules are linked together. B cells produce IgM first in response to microbial infection/antigen invasion.
Although IgM has a lower affinity for antigens than IgG, it has higher avidity for antigens because of its pentameric/hexameric structure. IgM, by binding to the cell surface receptor, also activates cell signaling pathways.

IgA is abundant in serum, nasal mucus, saliva, breast milk, and intestinal fluid, accounting for 10-15% of human immunoglobulins. IgA forms dimers (i.e., two IgA monomers joined together). IgA in breast milk protects the gastrointestinal tract of neonates from pathogens.

IgE is present in minute amounts, accounting for no more than 0.001% of human immunoglobulins. Its original role is to protect against parasites. In regions where the parasitic infection is rare, IgE is primarily involved in allergy.

IgD accounts for less than 1% of human immunoglobulins. IgD may be involved in the induction of antibody production in B cells, but its exact function remains unknown.

Antibody Classes and their biological Activities

Functions of Antibody

  • IgG provides long-term protection because it persists for months and years after the presence of the antigen that has triggered their production.
  • IgG protects against bacteria, viruses, neutralizes bacterial toxins, triggers complement protein systems, and binds antigens to enhance the effectiveness of phagocytosis.
  • The main function of IgA is to bind antigens on microbes before they invade tissues. It aggregates the antigens and keeps them in the secretions so when the secretion is expelled, so is the antigen.
  • IgA is also the first defense for mucosal surfaces such as the intestines, nose, and lungs.
  • IgM is involved in the ABO blood group antigens on the surface of RBCs.
  • IgM enhances the ingestions of cells by phagocytosis.
  • IgE bind to mast cells and basophils which participate in the immune response.
  • Some scientists think that IgE’s purpose is to stop parasites.
  • IgD is present on the surface of B cells and plays a role in the induction of antibody production.


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