The document details the characteristics and functions of various classes of antibodies, known as immunoglobulins, which are proteins formed in response to antigens. It describes the chemical nature of antibodies, their structure, and the specific roles of different immunoglobulin classes such as IgG, IgA, IgM, IgD, and IgE. Each class has distinct properties, concentrations, half-lives, and functions, such as providing immunity, protecting mucous membranes, and mediating hypersensitivity reactions.

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