It describes about Antibodies and their classification. Thier mode of function and their properties and structure . Role of different immunoglobulins.

2. • Antibodies are substances which are
formed in the serum and tissue
fluids in response to an antigen.
• Antibodies react with antigen
specifically.

3. • Properties of Antibodies:-
1.Chemical nature of antibodies
is globulin so they are named
as Immunoglobulins.
2.Serum globulins are separated
into pseudoglobulins (water
soluble) and euglobulins (water
insoluble).

4. • Structure of Immunoglobulin:-
- An Antibody molecule consists of
two identical heavy and light chains.
- The heavy (H) chains are longer and
light (L) chains are shorter.
- Both types of chains are polypeptide
in nature. The two heavy chains are
held together by disulphide (S-S)
bonds.

5. -Each light chain is also attached to
heavy chain by disulphide bonds.
-The H chains are structurally and
antigenically distinct in different
classes of immunoglobulins.
-The L chains are similar in all classes
of immunoglobulins. They are present
in two forms Kappa(K) and Lambda(L).

6. • Immunoglobulin classes:

8. Immunoglobulin G (Ig G):
 Ig G is the major serum immunoglobulin.
 The normal serum concentration is about
8-16mg/ml.
 Molecular weight is 150,000.
 Half life is about 23 days.
 It is the only immunoglobulin that is
transported through placenta and provides
natural passive immunity to the new born.
 It appears late but persists for a longer period.

9.  It is distributed equally between the
extravascular and intravascular compartments.
 It participates in precipitation, complement
fixation and neutralisation of toxin and viruses
 Ig G binds to microorganisms and enhances
the process of phagocytosis.
 There are four sub classes of Ig G:
- Ig G1 - Ig G3
- Ig G2 - Ig G4

10. Immunoglobulin A(Ig A):
 Ig A is the second major serum
immunoglobulin. The normal major serum
concentration is 0.6-4.2mg/ml.
 Half life is about 6-8 days.
 It occurs in two forms: serum IgA and
secretory IgA.
 Molecular weight of serum IgA is 160,000
and secretory IgA is 400,000.
 It is the principle immunoglobulin present
in secretions such as milk,tears,saliva,sweat.

11. It is also present in colostrum and in secretions
like respiratory, intestinal and genital systems.
 It protects the mucous membranes against
microorganisms.
 IgA does not fix complement but can activate
alternative complement pathway.
 IgA mainly synthesized locally by plasma cell
 There are two subclasses of Ig A:
-Ig A1
-Ig A2

12. Immunoglobulin M(Ig M):
 Ig M is a pentamer consisting of 5
immunoglobulin
 It constitutes about 5-8 percent of total serum
immunoglobulins.
 The normal level in serum is 0.5-2mg/ml.
 Half life is about 5 days.
 The molecular weight is 900,000 to 1,000,000
hence called ‘millionarie molecule’.
 IgM is mainly distributed intravascularly.
 It is the earliest synthesised immunoglobulin

13. by foetus in about 20 weeks of age.
 It appears early in respose to infection
before IgG.
 It is very effective antibody in agglutination,
complement fixation and opsonisation.
 IgM provides protection against blood
invasion by microorganisms
 There are two subclasses of IgM:
-IgM1
-IgM2

14. Immunoglobulin D (IgD):
 IgD is present in a concentration of 3mg per
100 ml in serum.
 Molecular weight is 1,80,000
 Half life is about three days.
 It is mostly intravascular in distribution.
 It is present on surface of unstimulated B
lymphocytes in blood and acts as
recognition receptors for antigens.
 There are two subclasses:
-IgD1 & IgD2.

15. Immunoglobulin E:
 It resembles IgG in structure.
 Molecular weight is about 190,000.
 Half life is 2-3 days.
 IgE is mainly produced in the linings of
respiratory and intestinal tracts.
 Serum contains only in traces.
 It is mostly distributed extravascularly.
 IgE mediates type 1 hypersensitivity
reaction. This is responsible for asthma,
hay fever.

16.  It has affinity for surface of tissue cells,
particularly mast cells of the same species.
 High level of IgE in serum is also seen in
children with a high load of intestinal
parasitism.
 It cannot cross the placental barrier or fix the
complement.
 IgE is responsible for anaphylactic type of
reaction.

17. Role of different Immunoglobulin classes:
 IgG – protects the body fluids
 IgA – protects the body surfaces
 IgM – protects the blood sream
 IgD – mediates reaginic hypersensitivity
 IgE – recognition molecule on the surface of
B lymphocytes