Antibodies, also known as immunoglobulins, are glycoproteins produced by plasma cells that recognize and bind to specific antigens. There are five classes of antibodies - IgG, IgM, IgA, IgD, and IgE - which are distinguished by their structure and functions. Antibodies are made up of two light polypeptide chains and two heavy polypeptide chains that form antigen binding sites. The different classes of antibodies play important but distinct roles in the immune response.

2.  Definition:
Glycoprotein molecules that are produced
by plasma cells in response to an immunogen
and which function as antibodies.

3.  Proteins that recognize and bind to a particular
antigen with very high specificity.
 Made in response to exposure to the antigen.
 Each antibody has at least two identical sites that
bind antigen: Antigen binding sites.

4. • Five classes of Antibodies- according to their
molecular weight, electrophoritic mobility,
ultracentrifugation sedimentation.
 IgG
 IgM
 IgA
 IgD
 IgE

6. Immunoglobulins are glycoproteins made up of:
- Four polypeptide chains (IgG): linked by disulfide
bonds
a- Two light (L) polypeptide chains – 212 A.A
b- Two heavy (H) polypeptide chains- 450 A.A
- Terminal portion of L-chain and H- chain contains
part of antigen binding site
-

8. - Each H-chain and each L-chain has V-region and
C-region
- V-region lies in amino terminal portion of molecule
- V-region shows wide variation in amino a. sequences

9.  5 different classes of H chains found in
humans on the basis of structural difference
 Mu (IgM)
 Delta (IgD)
 Gamma (IgG)
 Epsilon (IgE)
 Alpha (IgA)

10. On the basis of structural difference in
constant regions
 Kappa
 Lambda
Ig molecule contain identical K orλ chain but
never both.

11.  Both Heavy (H) and Light (L) chains have
repeating substructures known as domains.
 Each domain is approximately 110 amino
acids long, stabilized by intrachain
disulphide bonds.
 H chains usually contain 4 or 5 domains,
whereas L chains have only 2 domains

12.  The CH2 domain contains the complement-
binding site and the CH3 domain contains a
site that attaches to receptors on
neutrophils and macrophages.

13.  The disulphide bonds joining the antibody
heavy chains are located in a flexible region
of the heavy chain known as the hinge
region.

15.  Is an oligosaccharide with variable mono-
saccharide units.
 In IgG, the carbohydrate portion is about
2.5% of the total molecule and it is equally
divided between the two gamma heavy
chains- linked through amino acids, aspartic
acid and threonine residues in the
polypeptide chain.

16.  Antibody fragments are used in assay systems,
in the labortary.
 Papain and Pepsin are used routinely for the
preparation of fragments from IgG.

17.  Digestion of an immunoglobulin by the
enzyme papain produces
 two antigen-binding fragments (Fab) and
 one crystallizable fragment (Fc) , class-
defining fragments , which is responsible
for biological effector functions like
complement fixation, binding to
macrophages, natural killer cells and
neutrophils other than direct binding of
antigens.

19.  If pepsin is used cleavage occur on C
terminal side of inter H-chain disulphide
bonds, yeilding F(ab)2 fragment.
 fc portion is degraded.

23. I. IgG
Structure: Monomer, Heavy Chain class:
GAMMA
Percentage serum antibodies: 80%
Location: Blood, lymph, intestine
Half-life in serum: 23 days
Complement Fixation: Yes
Placental Transfer: Yes
Known Functions: Enhances phagocytosis,
neutralizes toxins and viruses, protects fetus
and newborn.

24. II. IgM
 Structure: Pentamer, Heavy chain: Mu
 Percentage serum antibodies: 5-10%
 Location: Blood, lymph, B cell surface (monomer)
 Half-life in serum: 5 days
 Complement Fixation: Yes
 Placental Transfer: No
 Known Functions: First antibodies produced during an
infection. Effective against microbes and agglutinating
antigens.

25. III. IgA
 Structure: Dimer, Heavy chain: ALPHA
 Percentage serum antibodies: 10-15%
 Location: Secretions (tears, saliva, intestine, milk),
blood and lymph.
 Half-life in serum: 6 days
 Complement Fixation: No
 Placental Transfer: No
 Known Functions: Localized protection of mucosal
surfaces. Provides immunity to infant digestive tract.

26. IV. IgD
 Structure: Monomer, Heavy chain: DELTA
 Percentage serum antibodies: 0.2%
 Location: B-cell surface, blood, and lymph
 Half-life in serum: 3 days
 Complement Fixation: No
 Placental Transfer: No
 Known Functions: In serum function is unknown. On B
cell surface, initiate immune response.

27. V. IgE
 Structure: Monomer, Heavy chain: EPSILON
 Percentage serum antibodies: 0.002%
 Location: Bound to mast cells and basophils
throughout body. Blood.
 Half-life in serum: 2 days
 Complement Fixation: No
 Placental Transfer: No
 Known Functions: Allergic reactions. Possibly lysis of
worms.

28.  Occurs during Immune Responses.
 antibodies with identical specificity but of
different classes are generated in a
specific chronologic order in response to
the immunogen (immunizing antigen).
 For instance, antibodies of the IgM class
normally precede molecules of the IgG
class. The switch from one class to another
is designated "class or isotype switching,"

29.  Agammaglobulinemia a gene defect that
blocks the growth of normal, mature immune
cells called B lymphocytes.
 Severe reduction in synthesis of an
immunoglobulin class can result in a serious
immunodeficiency disease—eg,, in which
production of IgG is markedly affected—
because of impairment of the body's
defense against microorganisms.

30.  Multiple myeloma is a neoplastic condition
electrophoresis of serum or urine will usually
reveal a large increase of one particular
immunoglobulin or one particular light chain
(the latter termed as Bence Jones protein).
but IgG are most common, followed by IgA
and IgM.