Immunity, Antibody, Antigen and Epitote

Immunity
-is the ability to produce lymphocytes or antibodies to destroy efficiently specific foreign substances such as antigens that has been detected by body.

Antibodies
-are specific proteins produced by B lymphocytes as as response to specific antigens detected in body.
-specific antibodies bind with specific antigens before the antigens are destroyed.
-Characteristics of antibodies:
.Each called Immunoglobulin-water soluble globular protein.
.Structure is 'Y' Shaped.
-Each molecule of antibody composes of:
.2 identical heavy chains (H chains) that are linked by disulphide bonds.
.2 identical light chains (L chains), each linked by disulphide bond to one H chains.
-Lower portion of the molecule is constant while 2 tips are variable.
-Both variable parts are antigen binding sites-each can bind specifically to same type of antigen like 'lock and key'.
-Immunoglobulin are divided into 5 groups: Immunoglobulin M, A, D, G, E.

Antigens
-foreign substances that stimulate the production of lymphocytes or antibodies in body specifically destroy them.
-Characteristics of antigens:
.Antigens are macromolecules-protein/polysaccharides/cojugated protein.
.Found on surface of micro-organisms, plasma membrane or as free molecules.
.Proteins produced in the same body cannot act as antigens but when it is transferred into another organism's body, they act as antigens.

Epitopes
-Small specific parts of a larger antigen which can bind with specific antibody.
-Characteristics of epitopes:
.Epitopes-antigenic determinant-may be more than one on an antigen.
.Each epitopes has specific configuration composed of certain side chains of amino acids or sugar.
-Bacteria-have more surface antigens-more epitopes-each epitopes capable of causing a specific antibody to bind with them.
-Viruses have fwer surface angtigens-fewer Epitopes.
-Macrophage that phagocytosise bacteria and viruses cuts its antigens into smaller epitopes which are then presented on the surface of the cell antigen-MHC complex for recognition by lymphocytes.