Glossary
IMMUNOGLOBULINS
Immunoglobulins are proteins that have antibody functions. They are produced by special cells that belong to the immune system in response to the presence of external agents such as viruses, bacteria, protozoa, fungi, cancer cells or extraneous tissues which are recognized as such by the presence of antigen molecules on their surface. Antibodies are produced in the blood by a particular type of cells, plasma cells, resulting from the differentiation of B lymphocytes in the presence of the antigen. Antibodies are responsible for recognizing the external agents and neutralizing the threat, in a variety of different ways. The shape of the antibody molecule can be represented as a Y, formed by four protein chains (two 'heavy' and two 'light' chains). Some sections of this molecule are the same across all antibodies, while others are specific to each type of antibody and determine its particular properties. Antibodies, also known as immunoglobulins, are generally abbreviated to Ig; according to the range of different structures and functions, they are grouped into five classes, indicated by the letters A, D, E, G and M. IgM immunoglobulins are the first type of antibody produced by babies, as well as the first that are synthesized in adults upon detection of infective agents. IgGs, or gamma globulin antibodies, are predominant in the serum and are produced when the organism is exposed to a specific antigen for the second time. IgE antibodies are produced as a result of allergic reactions. IgAs are constantly present in saliva, in the digestive tract and in breast milk. The role of IgDs is unknown. Antigen recognition by an antibody occurs specifically due to fact that the structure of the antibody is complementary to that of the antigen. This enables the two molecules to bind, similarly to a key matching its corresponding lock. Upon recognizing and binding to the antigenic substances on extraneous cells, antibodies can neutralize these cells in two ways: 1) by activating the complement system, whereby plasma proteins drill the cell’s membrane; 2) by activating special blood cells that engulf and destroy the intruders with a phagocytosis process.
After having been in contact with a given antigen, the body continues to produce specific antibodies for a given number of days; after reaching a maximum value, the production decreases and finally stops.
In some cases, the body retains the antibodies for that antigen thereby remaining permanently immunized, as occurs in some cases such as chickenpox. The production of antibodies in the body can be stimulated with the inoculation of vaccines. The types of antibodies that any organism can synthesize is extremely high, as is the number of substances that behave as antigens. In fact, any substance that is introduced into the body is foreign to it and can therefore act as antigen.
In some diseases, the body loses its ability to recognize some of its own components, developing antibodies against them. These are typically defined as autoimmune diseases, and include systemic lupus erythematosus and multiple sclerosis.
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• Glossary