Imunologi (Antigen and Antibody)

Antigen and Antibody

BY:
Thadly Chandra
Yestine Yuliantina

Overview of the Immune

1. Defend against extracellular pathogens by binding to antigens and making them easier targets for phagocytes and complement.2. Defend against intracellular pathogens and cancer by binding to ang lysing the infected cells or cancer cells.

 Antigen – Definition

•Is any substance that causes your immune system to prompts the generation of antibodies

•Antigens can be proteins, polysaccharides, conjugates of lipids with : proteins (lipoproteins) and polysaccharides (glycolipids)

•An antigen may be a foreign substance from the environment such as chemicals, bacteria, viruses, or pollen. 

•An antigen may also be formed within the body, as with bacterial toxins or tissue cells.

Antigen

•The body recognizes antigens by the three-dimensional  hapes or regions called antigenic determinants or epitopes.

     Properties that make molecules more effective antigens include:

§Stable molecules, ie, molecules that assume and maintain a definite shape

§Larger molecules with molecular masses between 5000 and 100,000 daltons

§Molecules that are structurally complex, with distinctive shapes and novel subunit combiniations

Origin of Antigens

Antigens can be classified in order of their class

•Exogenous antigens

•Endogenous antigens

•Autoantigens

Exogenous antigens

•Exogenous antigens are antigens that have entered the body from the outside, for example by inhalation, ingestion, or injection.

•Exogenous antigens (inhaled, ingested, or injected) are taken up by antigen-presenting cells (APCs)

•The immune system's response to exogenous antigens is often subclinical by endocytosis or phagocytosis.

Endogenous antigens

•Endogenous antigens are antigens that have been generated within cells as a result of normal cell metabolism, or because of viral or intracellular bacterial infection.

Autoantigens

•An autoantigen is usually a normal protein or complex of proteins (and sometimes DNA or RNA) that is recognized by the immune system of patients suffering from a specific autoimmune disease.

•These antigens under normal conditions, not be targeted of the immune system, but due to mainly genetic and environmental factors, the normal immunological tolerance for such an antigen has been lost in these patients.

Antibody Structure

•Antibodies are globular plasma proteins

•Antibodies are globular plasma proteins

•They have sugar chains added to some of their amino acid residues. In other words, antibodies are glycoprotein

•Produced by B-cell

•Are antigen-specific

•Bind and inactivate foreign particles

•The basic functional unit of each antibody is an immunoglobulin

Y-shaped molecule

Each antibody consists of four polypeptides - two heavy chains and two light chains connected by disulfide bonds, joined to form a "Y" shaped molecule.

•Although the general structure of all antibodies is very similar, a small region at the tip of the “Y” varies greatly among different antibodies

•This variable region, composed of 110-130 amino acids, allowing millions of antibodies with slightly different tip structures, or antigen binding sites

•The variable region includes the ends of the light and heavy chains.


Each antibody binds to a specific antigen; an interaction similar to a lock and key