immunoglobulins

1. IMMUNOGLOBULIN
S
Dr. Humera Kausar
2014
Immunology lecture # 5

2. Antibodies
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.

3. Antibody Structure
An antibody molecule is composed of two identical heavy
chains (H) and two identical light chains (L), each with a
variable region (V) constant region (C).

4. 45 kDa
50 kDa

5. 100kDa

6. Antibody Structure
Immunoglobulins are glycoproteins made up of:
- Four polypeptide chains (IgG):
a- Two light (L) polypeptide chains
b- Two heavy (H) polypeptide chains
- The four chains are linked by disulfide bonds
- Terminal portion of L-chain contains part of antigen binding site
- Terminal portion of H-chain participate in antigen binding site
- H-chains are distinct for each of the five Immunoglobulins
- The other (Carboxyl) terminal portion forms Fc fragment

7. Antibody Structure

8. Fine Structure of Antibody

10. Five classes of Antibodies:
* IgG
 IgM
 IgA
 IgD
 IgE

11. Immunoglobulin Classes
I. IgG
Structure: Monomer
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.

12. IgG ---- BIOLOGICAL ACTIVITY
 IgG1, IgG3 IgG4 readily cross the placenta and
play an important role in protecting the developing
fetus.
 IgG3 is the most effective complement activator,
followed by IgG1, IgG2 is less efficient and IgG4 is not
able to activate complement at all.

13. IgG ---- BIOLOGICAL ACTIVITY
IgG1 and IgG3 bind with high affinity to Fc receptor
on phagocytic cells and mediate opsonization.
IgG4 has an intermediate affinity for Fc receptors,
and IgG2 has an extremely low affinity.

14. Immunoglobulin Classes
II. IgM
Structure: Pentamer
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.

16. 1st Ig class produced in primary response to an antigen
and also 1st Ig to be synthesized by the neonate.
 More efficient than IgG at activating complement.
 Secreted by plasma cells as a pentamer. plays an
important accessory role as a secretory immunoglobulin.
 Five monomer units are held together by disulfide
bonds that link their carboxyl-terminal heavy chain
domains.

17. IgM --------- BIOLOGICAL ACTIVITY
Each IgM pentamer contains additional Fc linked
polypeptide called J-Chain, which is –S-S- bonded to
the carboxyl-terminal cystein residue of two of the ten
μ chains.
 J-Chain required for polymerization of monomers
to form pentameric IgM.
 J-Chain is added just before secretion of the
pentamer.
 Presence of J-Chain allows IgM to bind to receptors
on secretory cells, which transport it across epithelial
lining to enter the external secretions that bathe
mucosal surface.

18. Immunoglobulin Classes
III. IgA
Structure: Dimer
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.

19. Major Secretory Ig, present in saliva, tears,
milk, and mucus of bronchial, genitourinary
digestive tracts.
 Secretory IgA consists of a dimer or tetramer,
a j-chain polypeptide and a polypeptide chain
called secretory component.

22. IgA ---- BIOLOGICAL ACTIVITY
J-Chain polypeptide in IgA is identical to that
found in pentameric IgM serves similar
function in facilitating the polymerization of
both serum IgA and secretory IgA.
 Secretory component (70 kDa) consists of 5
Ig like domains.

23. IgA --- BIOLOGICAL ACTIVITY
Domains of secretory polypeptide binds to the
domains of IgA dimer and stabilized by a disulfide
bond.
 Every day , a human secretes 5 to 15 g of
secretory IgA in to mucous secretions.

24. Immunoglobulin Classes
IV. IgD
Structure: Monomer
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.

25.  Major membrane bond immunoglobulin expressed
by mature B cells.
 Its role in the physiology of B cells is under
investigation.
 No biological effector function has been identified
for IgD.

26. Immunoglobulin Classes
V. IgE
Structure: Monomer
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.

27.  IgE mediate the immediate hypersensitivity
reaction / allergic reaction.
 Ragweed pollen is a potent inducers of this class
of Ab.
 IgE binds to Fc receptors on the membranes of
Basophils and tissue mast cells.

28. Cross linkage of receptor bound IgE
molecules by Ag (allergens) induces Basophils
mast cells to translocate their granules to
the plasma membranes release contants to
the extracellular enviornment
(degranulation).

29. Antibodies
Function
Protective outcomes of
antibody-antigen binding
› Neutralization
 Prevents toxin from interacting with
cell
› Immobilization and prevention
of adherence
 Antibody bonding to cellular
structures to interfere with function
› Agglutination and precipitation
 Clumping of bacterial cells by
specific antibody
 Bacteria more easily phagocytized

30. Antibodies
Function
 Protective outcomes of
antibody-antigen binding
› Opsinization
 Coating of bacteria with antibody to
enhance phagocytosis
› Complement activation
 Antibody bonding triggers classical
pathway
› Antibody-dependent cellular
cytotoxicity
 Multiple antibodies bind a cell which
becomes target for certain cells

31. ا وہی ہے جس نے تمہیں مٹی سے پیدا
کیا پھر ایک وقت مقرر کر دیا اور اس
کےہاں ایک مدت مقرر ہے تم پھر بھی
( شک کرتے ہو ( 2
سُورَۡةُ اٴلنعَام