Antigen and Antibody

Antigen and antibody are two terms you might hear when talking about the immune system. An antigen is a molecule that triggers your body to produce antibodies while an antibody is a protein that binds to an antigen. Antigens and antibodies help the immune system to identify, recognize and destroy pathogens. Antigens help the immune system to distinguish between “self” and “non-self” while antibodies are produced to fight foreign substances such as viruses, bacteria and toxins. Antibodies are also important in fighting cancer cells and in preventing transplant rejection.

An antigen is a molecule that triggers an immune response in the body. The immune system identifies the antigens as foreign substances and remembers them to protect you from future exposure. When exposed to the same antigen, an immune cell called the B cell produces antibodies. A B cell reacts to the foreign substance by producing an antigen-binding site on its surface. The antigen-binding site recognizes and binds to specific proteins on the antigen. The bound B cell uses its surface protein called immunoglobulin which consists of two chains, one heavy chain and one light chain, to bind to the foreign invading pathogen or toxin. The B cell produces antibodies, also known as immunoglobulin, to attack and destroy the antigen. The inert immunoglobulin will be eliminated from the body through the gastrointestinal tract, urinary tract or skin surface. B cells will become exhausted if constantly producing antibodies.

B cells produce antibodies that bind to specific invaders in order to identify them as foreign and destroy them. A different type of immune cell called T cell uses B cells’ antibodies to detect and process antigens on pathogens or toxins that recognize them as non-self substances. The T helper cell recognizes that these molecules are hostile and should be destroyed by producing an immunological response to remove them from the body.

Antigen and Antibody: Difference

Antigen and Antibody Production

Antibodies are produced when a foreign substance penetrates the body. B cells recognize antigens as “non-self” and bind them to produce antibodies. Antigens trigger the immune system to produce antibodies that will attack and destroy invading antigens. A B cell produces both antigen-binding sites (variable regions) and immunoglobulin (constant regions). The different types of immunoglobulin have heavy chains that differ in size, amino acid sequence, behaviour and function. Antibodies are produced in the bone marrow, spleen and lymph nodes.

Location of Antibodies

An antibody is a soluble protein found in blood plasma or extracellular fluid. Antibodies are produced by B cells that travel through blood and lymphatic system to attack and destroy antigens. They will be eliminated through urine or gastrointestinal tract if not used to fight off antigens. An antigen is a protein located inside the cell membrane or extracellularly on the skin surface. Antigens are continuously shed from the body surface.

Antigens or Antibodies on Pathogens or Toxins

Antibodies and antigens are found on pathogens, toxins or cancer cells.

A bacteria may contain “self” proteins that would not be recognized as antigens but these proteins can trigger the immune system to produce antibodies against it. The antibody will bind to specific proteins in a foreign pathogen instead of a protein that is produced in the body by the immune system.

Conclusion

In this article, we discussed that there is a difference between antibodies and antigens. B cells produce antibodies to fight pathogens and toxins while an antigen is a molecule that triggers the immune system to produce antibodies. Antibodies are produced to fight against a specific type of organism or virus while antigen is not. Antibodies and antigens are found on viruses, bacteria, toxins and cancer cells. Antigens, not antibodies, would bind to these molecules since they are foreign substances that need to be destroyed by the immune system.