Antibodies are immunoglobulin proteins secreted by B-lymphocytes after stimulation by a specific antigen. The antibody formed binds to the specific antigen in order to mark the antigen for destruction.
The type of antigenic exposure occurring in the body determines if the antibody is a naturally occurring or immune antibody.
Naturally Occurring Antibodies
Naturally occurring antibodies can be formed after exposure to environmental agents that are similar to red cell antigens, such as bacteria, dust, or pollen. Sensitization through previous transfusions, pregnancy, or injections is not necessary. Some naturally occurring antibodies are present without a known environmental exposure.
- Antibodies are usually IgM and react best at room temperature or lower.
- Most of these antibodies are not clinically significant with the exception of ABO antibodies.
- Most people with healthy immune systems are expected to present with naturally occurring ABO antibodies appropriate for their ABO type. All other naturally occurring antibodies are considered "unexpected".
- Examples of naturally occurring antibodies include anti-A, anti-B, anti-Cw, anti-M, and antibodies in the, Ii, Lewis and P systems.
Immune antibodies occur in the serum of individuals who become sensitized to foreign antigens through pregnancy or transfusion. These antibodies are produced specifically against RBC antigens.
- IgM predominates in the primary response; IgG in the secondary response.
- Most react at 37°C and are considered clinically significant.
- Examples include antibodies in the K, Rh, Duffy, and Kidd systems.