When an antigen enters a cell, the specific carrier molecules in cell will carry the antigen to the surface of cell toward T lymphocyte cell. The carrier molecule is made up of a grow of genes called major histocompatibility complex (MHC).
Antibody is an immunoglobulin (Ig) protein which functions by giving response to antigen. Antibody is composed of heavy chain and light chain which at the end of the chain there is a specific antigen binding site.
Antibody can be found in blood and body fluid which is produced as an immune system response to foreign antigen. The antigen that is recognized by B lymphocyte, T lymphocyte, and macrophage will stimulate antibody release into the blood. The first cell response to antibody is the formation of IgM antibody by cell, and then it is followed by other types of antibody, such as IgG, IgA, IgD, and IgE.
a. IgM is the first antibody produced after the exposure to antigen, for example when a child receives tetanus I vaccination, 10-14 days later antibody antitetanus IgM (primary antibody response) will be formed. IgM is mostly found in blood, but in normal condition, there is no IgM found either in organ or tissues..
c. IgA is the antibody which plays a vital role in body defense against microorganism entering through mucosal surfaces, which are nose, eyes, lungs, and intestine. IgA can be found in blood and body fluid (in digestive tract, nose, eyes, lungs, and mother’s milk).
d. IgE is the antibody which causes acute allergic reaction (fast allergic reaction).
e. IgD is the antibody that is present in low levels in blood. The function is unknown yet.
Antibody stops the activities of antigen causing diseases by the following methods
a. Neutralizing; by binding antigen and preventing it from influencing the activity of normal cells.
b. Opsonization; preparing antigen for digestion by macrophage by coating the antigen surface with antibody.
c. Complement Fixation; making a hole and destroying the bacteria membrane by antibody.
Antibody can come out from blood toward another body fluid to prevent infection on mucosa surface, such as in small intestine and lungs. Antibody is also found in mother milk.