Different forms of antigens and antibodies are listed in a detailed format. Best for medical, dental and paramedical undergraduates.

1. Antigens and Antibodies
Dr. Jasmine Vinshia
Assistant Professor
Department Of Microbiology
Rajas Medical Institutions

2. Any substance which, when introduced parentrally into the
body stimulates the production of specific antibody.
– Complete antigen: induce antibody formation and specific
immune response by their own. Mol wt. >10,000 daltons.
– Partial Antigen (Hapten): A specific non-protein substance(Mol wt.
<10,000 daltons.) incapable of inducing antibody formation itself but
elicit immune response when couple with carrier protein.
• Complex Hapten : polyvalent – 2 or more antibody
combining site. Forms precipitate.
• Simple Hapten: univalent. Does not form precipitate.

3. Structure of An Antigen
• Epitope: Smallest unit of
antigen which combines with
antibody.
• Consist of 4-5 amino residues or
monosacharide residues
• Posses a specific chemical structure, electric
charge and spatial configration
• Capable of sensitizing any immune cell.
• Paratope: Site on antibody molecule which
binds with the epitope.

4. Properties of Antigen
• Size
– Antigenicity is related to molecular size
– Larger molecules are highly antigenic where as haptens are low molecular
weight having low antigenicity
• Chemical Nature
– Antigenicity is directly proportional to degree of structural diversity
– Amino acid(Protein)> Polysaccharides> lipid> nucleic acid
• Susceptibility
– Only substance that are metabolized by tissue enzyme to smaller antigenic
fragments can act as an antigen.
– Polystyrene are not antigenic whereas L-amino acids when broken down acts as
good antigens.

5. Properties of Antigen
• Foreignness
– Normal body contain numerous antigens or antigen producing substance which
may not produce antibody.
– But introduction of this into other body produces immune response
– This response is directly related to degree of foreignness – antigen from same
species shows less Antigenicity than others
• Antigenic Specificity
− Depending upon the antigenic determinant(Epitope) of an antigen, it has various
types:
A. Species specificity
B. Iso-specificity
C. Auto-specificity
D. Organ specificity

6. Antigenic Specificity
Species specificity
• All individual contain
species-specific antigens
• Ex: a individual sensitive
to horse serum will be
sensitive to other equine
but not with bovine
Iso-specificity
– Antigens found in the some but
not all members of species
– Blood grouping system is based on
this
– Genetically determined
Auto-specificity
• Sometime autologous antigens
starts showing antigenicity
• Autoimmunity disorders like
Rheumatoid arthritis, Sjogren
Syndrome
Organ Specificity
•Confined to a particular organ or
tissue.
•Organs like Kidney, brain, lens
protein etc sometimes share the same
antigens with other individuals.

8. These are specialized serum proteins which are produced in
response to antigenic stimulation. Also known as
Immunoglobulins.
•All antibodies are immunoglobulins, but all immunoglobulins
are not antibodies.
•Constitute about 20-25 % of total serum protein.
•Secreted by activated B cells and plasma cells
•Produced specifically as a result of antigen stimulation with
which it reacts specifically.

9. Structure Of An Antibody

10. Parts of an Antibody
• Y shaped immune molecule with 2 heavy chains(H) and 2
light chains(L) held together by disulphide bonds.
• Regions in an antibody:
1. Fab region: Fragment antigen binding. This portion
binds with the epitope of the antigen. Contains the variable
region of both heavy and light chains
2. Fc region: Fragment crystallizable. This portion binds to
the Antigen presenting cells such as macrophages for
initiating phagocytosis.

11. Heavy and Light Chains