Antibody

An antibody is a protein complex used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target.

Antibody structure
Antibodies are glycoproteins that are called immunoglobulins that are found in the blood and tissue fluids produced by cells of the immune system that bind to substances in the body that are recognized as foreign antigens. Antibodies stick to pathogens and work in a variety of ways to help eliminate the antigen that elicited their production. Some of the ways are independent of a particular class of immunoglobulins.

Immunoglobulins are grouped into five classes: IgG, IgA, IgM, IgD, and IgE.

• IgG is an immunoglobulin that is present in normal blood. This immunglobulin can bind to many kinds of pathogens, for example viruses, bacteria, and fungi to fight against toxins.
• IgA represent about 15 to 20% of immunoglobulins in the blood. This immunoglobulin helps to fight against pathogens that contact the body surface, ingested, or inhaled.
• IgM is an immunoglobulin that can detect whether a person has ABO blood type. It is also important in fighting bacteria.
• IgD immunoglobulins make up about 1% in the plasma membranes in B-lymphocytes. These immunoglobulins are involved in the development of plasma and memory cells that are in the B-lymphocytes.
• IgE is an immunoglobulin that can be found on the surface of the plasma membrane of basophils and mast cells of connective tissue. IgE can also be found in involved with diseases such as hypersensitivity and also in the defense of parasites such as worms.

Antibody function

Antibodies in the humoral immune response
Antibodies that recognize viruses can block these directly by their sheer size. The virus will be unable to dock to a cell and infect it, hindered by the antibody. Antibodies that recognize bacteria mark them for ingestion by macrophages. Together with the plasma component complement, antibodies can kill bacteria directly.

The way that antibodies work is by binding with the specific antigen for which the antibody is "designed". This formation of the antigen-antibody results in the stimulation of phagocytosis which is a procedure that cells engulf and destroy particles. An example of an antigen the can do this process is IgG antibodies that prevents the toxin harming the cell by sticking to the cell to destroy the it. Antibodies are less effective if they are in low concentrations meaning that it's sometimes less effective in taking care of an already established infection such as viral infections. A viral infection can hide from an antibody so that it does not destroy it when enters the cell but with bacterial infections they can be destroyed because they are outside of the cell.

Antibodies are effective in preventing any foreign antigens that go into the body. If an antibody can't take care of an already existing infection then it could be very effective in preventing an infection that is about to begin its process in targeting the cells.

Antibodies in the cell-mediated immune response
When a macrophage ingests a pathogen, it attaches parts of its proteins to a class II MHC protein. This complex is moved to the outside of the cell membrane, where it can be recognized by a T lymphocyte, which compares it to similar structures on the cell membrane of a B lymphocyte. If it finds a matching pair, the T lymphocyte activates the B lymphocyte, which starts producing antibodies. A B lymphocyte can only produce antibodies against the structure it presents on its surface.

Medical applications
"Designed" polyclonal antibodies are a potential weapon against cancer.

Applications in biochemistry
In biochemistry, antibodies are used for immunological identification of proteins (Western blot). Fluorescent antibodies are also used to locate proteins within a living cell.

References
Rhoades, Rodney and Richard Pflanzer. Human Physiology, Brooks/Cole, 4th edition

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