Unit 2 Flashcards
Define antigen
Any substance recognized as foreign by the body capable of provoking a specific immune response.
Antigens stimulate the formation of antibodies and development of cell-mediated immunity.
What are the characteristics of ABO antigens?
Found in red cells, lymphocytes, epithelial cells, organs, and tissue cells. Soluble antigens are detectable in secretions and all body fluids except cerebrospinal fluid.
ABO antigens exist as glycolipid or glycoprotein molecules.
When are ABO antigens detectable in utero?
5 to 6 weeks.
Full expression of adult levels is reached at about 2 to 4 years of age.
What is the difference between an immunogen and an antigen?
An immunogen is an antigen that is capable of eliciting an immune response in the body.
Immunogenicity can vary among individuals and at different times.
What are antigenic determinants?
Sites on an antigen recognized and bound by a particular antibody or T-cell receptor.
Also known as epitopes.
What factors contribute to the immunogenicity of an antigen?
- Chemical composition and complexity
- Degree of foreignness
- Size
- Dosage and antigen density
- Route of administration
Proteins are the best immunogens, followed by complex carbohydrates.
What are the two major types of antigens?
- Exogenous
- Endogenous
Exogenous antigens enter from outside the body; endogenous antigens are proteins found within human cells.
What are blood group antigens?
Chemical structures embedded in or protruding from RBCs, WBCs, and platelets.
They exist as glycoproteins, glycolipids, and proteins.
What is the basic structure of antibodies/immunoglobulins?
Composed of four polypeptide chains joined by disulfide bonds. Consists of light chains and heavy chains.
The variable region binds antigens; the constant region has unique antibody class functions.
What is the primary function of IgM?
First line of defense for bacterial infections and primary immune response.
IgM is the largest antibody molecule and can fix complement.
How does IgG function in the immune response?
Most abundant in plasma, can diffuse into interstitial fluid, and crosses the placenta.
IgG is produced in response to bacteria, viruses, and RBC/WBC alloantigens.
What percentage of the total circulatory Ig pool does IgA constitute?
About 10-15%.
IgA is produced in high concentrations by lymphoid tissues lining the GI, respiratory, and genitourinary tracts.
What is the role of IgE?
Mediates allergic reactions and immunity to invading parasites.
IgE activates mast cells causing immediate hypersensitivity reactions.
What is the significance of blood group antibodies in transfusion?
Evaluated by their ability to produce hemolytic transfusion reactions (HTR) or hemolytic disease of the fetus and newborn (HDFN).
This includes risks like anaphylaxis and graft-versus-host disease.
What is the hinge region of an antibody?
Imparts flexibility to the antibody structure.
It connects the Fab and Fc regions.
Fill in the blank: Antigens are detected in secretions and all body fluids except _______.
cerebrospinal fluid.
True or False: IgD is primarily a cell membrane Ig found on the surface of B lymphocytes.
True.
