The Distributions and Functions of

Immunogloblin Classes (Janeway 408 – 417)

Yusuf Ismaila F.

MOLECULAR IMMUNOLOGY

FACULTY OF MEDICINE

Date: Mi 08.05.2019

2 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Immunoglobulin

Glycoprotein produced in

response to an antigen

Produced by B

Lymphocytes

Found in Serum

It is symmetrical with two

light chain (25 kDa) and

two heavy chain (50

kDa)

Deficiency is life

threatening.

3 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

IgM

Pentamer

Produced in

humoral immune

response

Expressed without

class switching

Blood, Lymph, B cell

(Monomer)

Stayed and protect

the blood stream

Best Complement

Activation.

4 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Monomer

About four isotype

Most abundant Ig in

circulating fluid

Protect extracellular

space within tissue

Enhances phagocytosis

Neutralizes toxins and

viruses

Protects fetus and

newborn

Compliment activation

5 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Dimer in Secretion but

Monomer in circulation

Principal class in

Secretion (tears, saliva,

intestine and milk)

Operate mainly in

Epithelial Surface

Act as a neutralizing

antibody

Protection of Epithelial

Surfaces

6 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Always a monomer

Very low level in Blood

Bound to mast cells

Induction of Allergic

reaction.

7 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

IgD Monomer

Located in Blood,

lymph and B-cell

In serum function is

unknown.

It is co-expressed with

IgM

On B cell surface,

initiate immune

response.

8 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Antibodies of different classes are adapted to function in

different compartment of the body.

The distribution of antibodies is determined by their heavy

chain isotype which can limit their diffusion.

Immunoglobulin binds to polymeric immunoglobulin

receptor (pIgR) which transport them to their site of

function in a process known as transcytosis

Upon reaching their destination, pIgR is cleaved to

release the antibody with SC remain bound to the

antibody which serve a lot of physiological roles

Neonatal Fc receptor transport antibody to neonate.

Distribution of Antibodies

9 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Overview of the distribution of

Immunoglobulin

The tail region of immunoglobulin (Fc) interacts with cell

surface receptors (Fc receptor) which facilitate their

distribution.

10 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Overview of the functions of Immunoglobulin

Each human immunoglobulin has a specialize

function with respect to there distribution.

11 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

IgG and IgM dominate in

Blood

IgG and IgA (monomer)

dominate in extracellular fluid

Dimeric IgA predominate in

secretions including breast

milk

IgE bound to mast cells

(epithelial surfaces)

The brain is devoid of

Immunoglobulin

Immunoglobulin Classes are

selectively distributed in the body

12 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

IgA neutralize pathogens and toxins in

the gut lumen

13 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

IgG and IgA

binds to various

bacteria toxins

with high affinity

and neutralize

the toxins.

Basic principle of

immunization

14 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Neutralization of toxins by IgG antibodies

15 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

IgG and IgA antibodies inhibit the infectivity of

viruses

16 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Antibodies prevent the attachment of

bacteria to cell surfaces

IgA and IgG neutralize the

adhesins secreted by bacteria

for attachment to cell surface

17 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Antibody and Antigen

complexes activate

the classical pathway

C1q bind to Fc

C1r (active enzyme)

Cleavage of C1s to

generate serine

proteases that initiate

the classical

complement cascade

18 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Erythrocyte Complement Receptor

1 (CR1) helps to clear immune

complexes from the circulation.

Immune complexes bind to CR1

on erythrocytes

Liver and spleen, removed by

macrophages

Transported

19 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

Each antibody is specialized both in its localization and in functions

IgM are found mainly in blood, they are pentameric and best activator

of complement system

IgG are found in blood and in extracellular fluid where they neutralize

or opsonize toxins and activate complement system

IgA dimers are found in epithelial surface where they protect the

epithelial surface.

IgE is bound to mast cell where they induce allergic response

Antibody defend the body by neutralizing toxins or by preventing the

binding of pathogen to the cell surface

IgM and IgG activate the classical complement pathway

Immune complexes are cleared via complement receptor on

erythrocytes.

Summary

20 The Distributions and functions of Immunoglobulin classes

Yusuf Ismaila Francis | 08.05.2019 | Immunology | Seminar

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