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Antigen themself stimulate immune response and they are both antigenic and immunogenic in nature.

Antigen: Antigen is a kind of substance that is capable of stimulating an immune response that mainly stimulates lymphocytes which fight against infection and this fighting cell known as white blood cells. Antigen themself stimulate immune response and they are both antigenic and immunogenic in nature. Mainly antigen is divided into two types: one is foreign antigen known as heteroantigens and other is antigen which originates within the body known as autoantigens, example:autoimmune disorder. When antigen enters the body it provokes lymphocytes to produce antibodies and this process is known as immunogen.  An antigen that  induces  humoral and/or cell-mediated immune response,this ability is called immunogenicity. whereas antigens are any substance that binds specifically to an antibody or a T-cell receptor. Thus we can say that all immunogen are antigen but all antigen are not immunogenic. Most of antigens are proteins but some are carbohydrates, lipids, and nucleic acids. Active regions of an immunogen that binds to an antigen-specific membrane receptor known as Epitope. This surface is also called as antigen-determinants. Types of Antigen:

Diagram of Antigen Versus Antibody: [Image will be Uploaded Soon] Properties of Antigens: Antigens have following features:

  Structure of Antigens: The antigenic determinants are the components of antigen and every antigen has several epitopes. Whereas every antibody has at least two binding sites and that site binds to specific antigens and every antigen has several epitopes. The antigen combines with antibodies like lock and key mechanism. The ability of the body to fight against antigen is termed an immunity. This immunity may be inborn or acquired by indirect mode like vaccination known as innate immunity.   Types of Immunity: 1.Innate Immunity- It is also called as the natural immunity, as it is inherited from the parents to their young ones and protects from birth throughout the life period.

Interaction of Antigen with Antibody: Interaction between antigen and antibody is very specific as they are totally dependent on hydrogen bonding, electrostatic force and van der waals forces.there interaction is of weak, non covalent nature but some interaction of antigen and antibody are strong in nature. In case either they are multivalent in nature or they have multiple copies of epitopes, under these cases they form stabilized complexes, thus reducing possibility for binding. All antigen binding process is a reversible process and they follow the basic thermodynamic principle of any reversible bimolecular interaction reaction: where KA is the affinity constant, (Ab-Ag) is the molar concentration of the antibody-antigen complex and (Ab) and (Ag) are the molar concentration. Nature of Antigen-Antibody Bond: The Binding site of an antibody is located in the F(ab) portion of the antibody molecule and is assembled to heavy and light chains. These binding sites have following features:

Factors Affecting Antigen-Antibody: There are several factors which determine rate of antigen-antibody reaction, these factors are given below:

An antigen that  induces  humoral and/or cell-mediated immune response, this ability is called immunogenicity.

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They are capable of eliciting an immune response by an organism’s immune system

Antigen refers to a molecule that is capable of binding to the product of that immune response.