Major Differences between Antigens (Ags) & Antibodies (Abs)

  An antigen is any foreign molecule that interact with cells of immune system and could induce an immune response.
  Antibodies are globular proteins or immunoglobulins that react specifically with antigen that stimulated their production.
These are the basic difference between Antigens and Antibodies.

Major differences between Antigen and Antibody

Difference No.1: Definition


  • Antigens are any substance or molecules that interact with antibodies or by T cell receptor when complexed with MHC are called antigens.
  • It include components of cell walls, capsules, flagella, toxins, viral proteins, bacteria and other microorganisms.
  • Theoretically any foreign body that is capable of inducing an immune response can be called as an antigen.


  • Antibodies are globular proteins or immunoglobulins synthesized by plasma cells of B cells that react specifically with antigen that stimulated antibody production.
  • There are millions of antibodies inside our body that is specifically designed against different antigens in the surrounding.

Difference No.2 Chemical Nature


  • Antigens are generally proteins but can be carbohydrates, lipids or even nucleic acids.
  • In the case of virus carbohydrate polysaccharide can be antigen.


  • Antibodies are glycoproteins made up of amino acids and small amount of carbohydrates.
  • Antibodies also called immunoglobulins.

Difference No.3 : Basic Structure


  • Antigenic structure is highly complex in structure and composition.
  • Antigens can be Simple to complex.
  • Each antigen will interact with a specific antibody, this interactions is highly specific.


  • Antibody's 'Y' shaped structure consisting of 4 polypeptide chains, 2 heavy chains (H-chains) and 2 light chains (L-chains) joined by disulphide bonds.
  • Each antibody contains two antigen binding site at the Fab region (variable region).

Difference No.4 : Interactions


  • The region of the antigen that interacts with the antibodies is called epitopes.
  • A pathogen has many epitopes.
  • This epitope interaction specifically with different antibodies.


  • The variable region of the antibody that specifically binds to an epitope of antigen is called paratope.
  • Generally, a Y shaped antibody like IgG has 2 identical paratopes.

Difference No.5 : Role in Immune System


  • Antigens causes disease or allergic reaction.
  • E.g. Cholera, Malaria, Polio, HIV etc.


  • Antibodies are involved in our defence system.
  • Protects the system by immobilisation or lysis, agglutination, precipitation of antigenic material.
  • Antibodies are the master molecules that is protecting us from diseases.