Let’s study antibodies, one of the most powerful weapons used by a special type of a body soldier called plasma cells
Get to know all about antibodies structure, function and mechanism of action by visiting the link below.
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Antibodies, also called immunoglobulins (Ig) are Y-shaped Glycoproteins produced by a differentiated type of B-cells called plasma cell.
How B-cells differentiate into plasma cells
B-cells are special type of lymphocytes produced in the bone marrow together with the t-cells and other form of white blood cells as well as red blood cells. The B-cells matures in the bone marrow in contrary to T-cells another type of lymphocytes that migrated to the thymus tissues for maturation.
B-cells, like the dendritic cells and macrophages have antigen-presenting ability. B-cells engulf antigens (bacteria) and present the antigens of their cells in form if MHC II (Major Histocompatibility Complex II) that is recognized by T-cells which makes the final blow that lead to the elimination of antigen in the body. The binding of CD4+ T-cell to the B-cells this leads to it’s activation and subsequent differentiation into Memory B-cells and plasma cells
The memory B-cells store information about a particular antigen and cause elevated immune response upon subsequent encounter with which microorganism while the plasma cells secrete antibodies.
Functions of antibodies
The major roles performed by antibodies in the body include:
- Neutralization
- Opsonisation
Antibodies neutralizes the effectiveness of antigens (viruses and bacteria) by binding to their surfaces thus making them unable to attack red blood cells
Opsonization is also another function of antibodies. They bind to surfaces of antigens and make it readily available for phagocytic cells for engulfment and complement proteins which causes the lysis of the bacteria cells or in other hands make it available for phagocytic cells engulfment.
Structure of Antibodies
The antibodies structure is referred to as dimers of dimers, containing two heavy chains and two light chains. The molecular weight of the heavy chains are. 50000Da while the light chains is exactly the half of the heavy chains. Molecular weight of light chains are 25,000Da
Antibodies are classified into five based on their heavy chains:
- IgG (Gamma heavy chains)
- IgM (Mu heavy chains)
- IgD (Delta heavy chains)
- IgE (Epsilon heavy chains)
- IgA (Alpha heavy chains)
While there are two types of light chains in the antibody:
- Kappa (κ) light Chains
- Lambda light (λ) chains
The carbohydrate residue of the antibodies gives antibodies it’s solubility. In the antibody is a region known as hinge region that provide the antibody with some flexibility. It should however be noted that only three classes of antibodies possess hi g region: IgA, IgG and IgD while IgM and IgE possess no hinge region. Another important region is known as the fragment crystallizable (Fc) region as well as the Fab region (The region responsible for antigens binding region) which is responsible for antigens binding.
The antibody structure is also made up of variable regions which are composer of amino acids
The structure of the antibody is held together firmly by disulfide bridges
Classes of antibodies and their functions
- IgG: possess Gamma (ᵞ) heavy chain. It is a major secondary immune response to appear at a site of infections. It also helps to cause bacterial immobilizations and in the neutralization of viral toxins. This is the only antibody that can cross the placenta and provide immunity to fetus.
- IgM possess Mu (µ) heavy chain. It is the first antibody produced against antigens during infection
- IgD possess Delta (ᵟ) heavy chain. It plays a major role in the maturation of B-cells. It is found in the
- IgE is composed of Epislon (ε) heavy chain (73,000 Da). Immunoglobulin E plays a vital role in hypersensitivity reaction, it is responsible for asthmatic reaction and anaphylactic shock.
- IgA possess an Alpha (α) heavy chain. It is the Immunoglobulin predominantly found external secretions such as breast milk, saliva, tears and mucus of bronchial, genitourinary and digestive tracts. IgA can cross the epithelial layer and enter into body secretion and provides local immunity in GI tracts, respiratory tract, and genital tract. IgA also neutralize viral toxins and inhibit their attachment on host surfaces.
Structurally, both IgG, IgD and IgE exist in monomeric form while Ig M exist in pentameric form and IgA in dimeric form.
