b ig genetics.ppt

8/11/2019 B Ig Genetics.ppt

1/17

Immunoglobulin Genetics


2/17

Immunoglobulin Genetics

History

Same C region could associate with many V regions

IgG Ab with different specificities

Same V region could associate with many C regions

Same idiotype on IgG and IgM Ab

V and C regions coded for by separate genes


3/17

Light Chain Gene Families

Germ line gene organization

J1

C1

E

J2

C2

E

J3

C3

E

J4

C4

EP

L V1

P

L Vn

P

L V2

Lambda light chain genes; n=30

P

L V 1

P

L V n

P

L V 2 J

2 J

3 J

5 C

E

J

1 J

4

Kappa light chain genes; n=300


4/17

Light Chain Gene FamiliesGene rearrangement and expression

L V1 L VnL V2 J

2 J

3 J

5 C

J

1 J

4

DNAP PP E

P P E

L V1 L J

5 C

V2 J4

DNA

DNA Rearrangement

V CJ

V C

Protein

Transport to ER

Protein

TranslationCL V J

E

L V CJ

RNA

Transcription

Primary transcript

CL V JRNA Processing

RNAmRNA


5/17

Heavy Chain Gene FamilyGerm line gene organization

Introns separate exons coding for H chain domains

Heavy chain genes; Vn=1000, Dn=15

P

L V1

P

L Vn

P

L V2 D2 D3D1 Dn

C

C

C

3

C

C2

C1

C4

C

1

C

2

J2 J3 J5J1 J4

E

CH1 H CH2 CH3 CH4


6/17

Heavy Chain Gene FamilyGene rearrangement and expression

P

L V1

P

L Vn

P

L V2 D2 D3D1 DnC

C

J2 J3 J5J1 J4

E

DJ rearrangement

P

L Vn

P

L V1

P

L V2D2

D1 C CJ5J4

EDNA

VDJ rearrangement

D2 C

C

J5J4

EP

L V1

P

LV2

DNA

Transcription

D2 C

C

J5J4

E

LV2

RNAPrimary transcript


7/17

Heavy Chain Gene FamilyGene rearrangement and expression

EPrimary transcript

E

J4D2V2 C

C

J5L C

C

J5L D2 J4V2

RNA Processing

An

mRNA for C

C

L DJV C

L DJV

An

mRNA for C

Translation

C

heavy chain

C

L DJV C

L DJV

C

heavy

chain

Transport to ER

C

heavy chain

V C

C

DJV C

DJV

C

heavy

chain

V C


8/17

Mechanism of DNA Rearrangements

Recombination

signal sequences

(RSS) Nonmer

Heptamer

1 or 2 turn signals

Rag-1 and Rag-2

L V

2

J C

1

Lambda light chains

L V

1

J C

2

Kappa light chains

Heavy chains

L V

2

J C

211

D

Heptamer

CACAGTG

GTGTCAC

Nonamer

ACAAAAACC

TGTTTTTGG

23 bp

23 bp

Two turn

RSS

2

Nonamer

GGTTTTTGT

CCAAAAACA

Heptamer

CACTGTG

GTGACAC

12 bp

12 bp

One turn

RSS1


9/17

Order of Ig Gene Expression

+

-

Heavy chain gene

VDJ recombination

Productive rearrangement ?

Yes

No

Transcribe/translate

1st

2nd

or

Apoptosis

Progenitor B cell

Pre B cell

() Heavy chain

PaternalMaternal


10/17


+

-

Light chain gene

VJ recombination

Productive rearrangement ?

Yes

No

Transcribe/translate

Light chain

4 th

Apoptosis

1st -

2nd -

3rd -

4th -

or

Pre B cell

Mature B cell

+


11/17


Explains: Why an individual B cell only produces one

kind of Ig with one kind of heavy and one

kind of light chain

Why an individual B cell makes only makes

antibodies of one specificity

Why there is allelic exclusion


12/17

Origin of Antibody Diversity

History

Definition Diversity (repitoire) is the total

of all the Ab specificities that an organism

is capable of expressing

Theories

Germ line theory

Somatic mutation theory


13/17

Origin of Antibody DiversityCurrent concepts

Multiple V genes

V-J and V-D-J joining

Junctional diversity

N region insertionsAmino acid

sequences notencoded in the germ

line

D region

T GGC CC

Pro Trp

CC C C C C

V gene

T GG

D region

CC C C C C

V gene

T GG

C GGC CC

Pro Arg

CC C C C C

V gene

T GG

D region

C GCC CC

Pro Pro


14/17

-GTCAATG

-GTCAATG- +

Break DNA

TdT adds nucleotides

Ligate

N region insertion Intron

JD

J

J

J

D

D

D

Generation of N region insertions


15/17

Origin of Antibody Diversity

Current concepts

Multiple V genes

V-J and V-D-J joining

Junctional diversity

N region insertions

Somatic mutation

Combinatorial association

Multispecificity


16/17

Generation of Diversity

B cell receptor(Immunoglobulin)

Heavy Light

V gene segments 1000 300

D gene segments 15 -

J gene segments 4 4

N region insertion ++ -

Junctional diversity +++ +

Somatic mutation + +

V x D x J

1000 x 15 x 4

V x J

300 x 4Total 6 x 10

4 1.2 x 10

3

Combinatorial association 7.2 x 107

Ag independent process Clonal selection


17/17

T Cell Antigen Receptor

Heterodimer of anand achain

Gene structure and expression of thechain is

analogous to the immunoglobulin heavy chain Gene structure and expression of thechain is

analogous to the immunoglobulin light chain

No somatic mutation in T cells

b ig genetics.ppt

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