Immunology pdf - د. محمد

Lecture 2

Immunoglobulin

Objectives;
Define secretary IgA
Describe structure & functions of IgM
Compare the antigenic receptor of B

lymphocyte

Assess the role of IgE in Atopy
Distinguish between Isotype, Allotype &

Idiotype

Explain Anti-idiotype Ab
List the characteristic of specific

Immune response

Compare between primary &

secondary Immune Response

IgA

Constitute 15% of total serum Ig

Main Ig in

the external secretions

as saliva

tears breast milk

Subdivided into IgA1 & IgA2 subclasses

It has 2 forms ;

1-Monomeric in the blood

2- dimeric in the external secretions

Dimeric IgA

• IgA synthesized by plasma cell as monomeric

one in the submucosa which will be combine
with another monomeric IgA by a
polypeptide J chain to form dimeric IgA this
will be protected by a secretary piece from
the secretary epithelium to form the

secretary IgA

Secretory piece(

. Produced by

mucosa epithelial cells

Secretory IgA (sIgA)

. Functions:

protect sIgA, resist proteolysis in

extra secretory liquid.

IgA

J chain

Ⅲ. IgA

1. Two types

Serum type

：

monomer

Secretary type（sIgA）

: dimer

2. Two subclasses：IgA1，IgA2

Functions of secretary IgA

Activation of the complement

through the alternative pathway

Blocking & Neutrilization
opsonization

IgM

• Constitute 10% of total serum Ig
• Its molecular weight 900 000 (

Heavy

)

• It has 2 forms

1-Monomeric form on the surface of

lymphocytes as antigen Receptor

together with IgD

pentameri

c IgM 5 monomeric connected

by J chain

Pentameric IgM

• IgM has no hinge region replaced by an

additional domiain(CH2)---CH3,CH4

• Pentameric IgM has 10 FAB so it is the most

agglutinating & complement fixing Ab

• It is the main Ig in the primary immune

response

• It is the 1

Ig synthetized by the fetus

IgD

Very low concentration in the blood less
than 1%
Short half life 2-3 days
Present on the surface of B lymphocyte
together with monomeric IgM as a

surface

antigen receptor of B lymphocyte

Immature B cell only IgM on its surface

Mature B cell IgM+IgD on its

surface

IgD

IgE

• 0.002 % of serum Ig ( detection by Elisa)
• In atopic patient the level increase by

handreds

• IgE also called

Reagenic or homocytotropic Ab

because of its ability of binding to FC
receptors on the surface of

Mast cells

basophiles

degranulation

IgE

allergen

inflammation

Functions of IgE

• Triggering an acute inflammatory reaction

• Has the ability to bind to FC receptor on

eosinophils so

important against parasitic

infections

eosinophils contain granules that realize cat

Ionic proteins which are toxic to the parasites

IgE increases in

• Parasitic infections
• Atopic patients

IL 4 causes switching of Ig to IgE

IL 5 causes eosinophilia

degranulation

IgE

allergen

inflammation

Variants of Ig

• Isotype

all classes ,Subclasses & forms of Ig

which present in normal individual

• Allotype

existence of allelic forms , single a.a.

variation in the peptide chain of Ig ( genetic
marker) IgG =GM, IgA=AM

• Idiotype

each Ig has its own antigenic

determinant area against which an anti-
idiotype Ab will be formed (Idiotype

•

antiidiotype network)

A.I. vaccine

Anti idiotype vaccine

Characteristics of sp. Immune respond :

1-Discrimination (distinguish) between self &
Foreign Ag

Any Ag when reach the lymphoid tissue during

pre-natal period suppress any further
immunological response to that Ag in future
((self))

colonel deletion theory

During embryonic dev. All T & B lymphocytes that

carry auto –reactive receptors for self Ag
( (

Auto-reactive cells

) will be deleted by

apoptosis

self tolerance

2- specificity

Ab react specifically with Ag that causes its

production ,sometimes can react with similar
not identical = cross reaction

β- haemolytic streptococci can lead to

rheumatic heart dis

. Because cross reaction

between bacteria Ag & valve tissue in some
individuals

3-clonality

We have more that 10 T & B lymphocytic

clones (group) each clone with different Ag
receptor, when the Ag enter the body
lymphocytes bearing receptors that fit the
epitope best are stimulated to divided

(clonal selection theory)

this response is

called

primary immune response

Clonal Selection of B Cells is Caused by

Antigenic Stimulation

B lymphocyte development (2)

4-Anamnest response :(memory)

The primary I.R. (1

exposure)

a-Lag phase (7days) Ab level is zero (time for

finding appropriate Ag receptor) depend on
nature ,routs, immune state

b-Log phase Ab(mainly IgM) start to appear &

increase logarythemly

c-Plateau phase
d-decline phase

Secondary I.R. (2

exposure)

there is

memory

cell so no lag

phase ,Ab titer quickly shooting

up 10-100 times

*There is genetic switching from

IgM in the pri. I.R. to

IgG

in the

I.R.

Primary I.R.

Secondary I.R.

* There is lag phase

*No lag phase

*IgM class

*Ab of IgG class

*Low affinity Ab

*Ab of high affinity

*Ab titer is low

*Ab titer is high

*The host exposure for the
1

time so no memory cell

*Host exposure for the 2

time there is memory cell

*Ab titer decline rapidly

*Ab titer decline slowly

Best example is the

vaccination

give booster

Doses(multiple doses) to shift the I.R.
from primary to secondary I.R.

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