3. Introduction
• Definitions
• Antigen: any substance capable, under appropriate conditions, of inducing a specific
IMMUNE RESPONSE and reacting with the products
of that response; that is, with specific ANTIBODY or specifically sensitized T LYMPHOCY
TES
• Immunogen: Any substance that can elicit an immune response
• Epitope: site on the surface of an antigen molecule to which a single antibody molecul
e binds; an antigen has several or many different antigenic determinants and reacts wit
h differrent antibodies
4. Introduction
• Paratope: a site on the antibody molecule that binds to an antigen
• Haptens: are small molecules that elicit an immune response only
when attached to a large carrier such as a protein; the carrier may be
one that also does not elicit an immune response by itself
5. Introduction
• Glycoprotein molecules that are present on B cells (BCR) or
produced by plasma cells (usually referred to as antibodies) in
response to an immunogen
• Are capable of binding specifically with a specific antigen
• There are five classes of antibodies: IgD, IgM, IgG, IgA, and IgE
6. Function of antibodies
• Neutralization
Antibodies bind to and block specific sites on viruses and bacteria,
thus preventing these antigens from binding to receptors on tissue cells
• Opsonization
Enhanced phagocytosis
• Antibody dependent cell cytoxicity (ADCC)
Antibody depended cell cytotoxic
• Fixing complement
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11. Class of antibodies
• Sequence analysis of the heavy chains shows five different types of heavy
chains named:
• IgM
• IgG
• IgE
• IgD
• IgA
12. Antibody classes and biological activities
• Immunoglobulin G (IgG)
IgG, the most abundant class in serum, constitutes about 80% of the total
serum immunoglobulin
IgG1 readily cross the placenta and play an important role in protecting the
developing fetus
IgG3 is the most effective complement activator.
IgG mediate phagocytosis by opsonization.
13. Antibody classes and biological activities
• Immunoglobulin M (IgM)
• IgM accounts for 5%–10% of the total serum immunoglobulin
• IgM is the first immunoglobulin class produced in a primary response
to an antigen, and it is also the first immunoglobulin to be synthesized
by the neonate
• IgM is also more efficient than IgG at activating complement
14. Antibody classes and biological activities
• Immunoglobulin A (IgA)
• Although IgA constitutes only 10%–15% of the total immunoglobulin
in serum
• it is the predominant immunoglobulin class in external secretions such
as breast milk, saliva, tears, and mucus of the bronchial, genitourinary,
and digestive tract
15. Antibody classes and biological activities
• Secretory IgA has been shown to provide an important line of defense
against bacteria such as Salmonella, Vibrio cholerae, and Neisseria
gonorrhoeae and viruses such as polio, influenza, and reovirus
• Breast milk contains secretory IgA and many other molecules that help
protect the newborn against infection during the first month of life
• Because the immune system of infants is not fully functional, breast-
feeding plays an important role in maintaining the health of newborns
16. Antibody classes and biological activities
• Immunoglobulin E (IgE)
• low average serum concentration(0.3 g/ml)
• IgE antibodies mediate the immediate hypersensitivity reactions that are
responsible for the symptoms of hay fever, asthma, hives, and anaphylactic shock
• IgE binds to Fc receptors on the membranes of blood basophils and tissue mast
cells. Cross-linkage of receptor bound IgE molecules by antigen (allergen) induces
basophils and mast cells degranulation
17. Antibody classes and biological activities
• Immunoglobulin D
• IgD, together with IgM, is the major membrane bound
immunoglobulin expressed by mature B cells, and its role in the
physiology of B cells is under investigation
• No biological effector function has been identified for IgD
