LIGHT CHAIN

HEAVY CHAIN

Polypeptide

Gene Segments

Variable Constant

J CV

Variable

V

o s aC n t nt

D J CH1 CH2 CH3

Polypeptide

Gene Segments

Light Chain POLYPEPTIDE

Light Chain GENE SEGMENTS

H.C.POLYPEPTIDE

H.C. GENE SEGMENTS

Ig Polypeptides Are Encoded by Multiple Gene Segments

About 100V gene segments

4 J GeneSegments

1 C GeneSegment

A Prototype Ig Gene: Murine Kappa

Multiple V gene segments, distant from J and C

A few J gene segments

One C gene segment

Murine Ig Heavy Chain Gene Organization

C C C3 C1 C2b C2a C C

~ 120 V Gene Segments ~20 Ds 4 Js 8 Constant Gene Segments

L VH

C1 C2 C3 C4/S CM

Figure 4-4Human Ig Loci

TCR Alpha and Beta Loci

TCR Delta and Gamma Loci

IMMUNOGLOBULIN GENES UNDERGO TWO DNA REARRANGEMENTS

1. V(D)J Recombination: both light and heavy

chains

2. Class switch recombination: heavy

chains only

Figure 4-2DNA Rearrangement RemovesSequences Between V, D and J Segments

RNA Splicing Removes Sequences Between J and C Segments

DNA

RNA

Figure 4-6V(D)J recombinationinvolves DELETION of DNA betweenV, D and J codingsegments.

The deleted DNA is LOST from the cellbecause it is notreplicated.

Figure 4-5

Recombination Signal Sequences (RSSs)Flank Rearranging Gene Segments

7bp 9bp12/23 bpRSS=heptamer, spacer and nonamer

Figure 4-7

Initiation ofV(D)Jrearrangement :RAG-dependentcleavage

Resolutionof cleavageproducts:DNA non-homologousend-joiningmachinery

#1:Lymphocyte-Specific

#2:Constitutive

Figure 4-8

Addition of Bases at V-D-J Junctions:An Important Source of Diversity

Figure 7-18

CONSEQUENCES OF V(D)J RECOMBINATION

1. Combinatorial diversity: # of possible combinationsis the product of the # of recombining segments

i.e. for mouse h.c.: 120x20x4=104

2. Junctional diversity at CDR3Deletion of bases at junctionsN region additions at junctionsP region additions at junctions

3. Activates transcription of the rearranged geneJuxtaposition of intronic enhancers with V regionpromoters.

4. Allows receptor editing to alter potentially self-reactive antibodies

LIGHT CHAIN

HEAVY CHAIN

Polypeptide

Gene Segments

Variable Constant

J CV

Variable

V

o s aC n t nt

D J CH1 CH2 CH3

Polypeptide

Gene Segments

Light Chain POLYPEPTIDE

Light Chain GENE SEGMENTS

H.C.POLYPEPTIDE

H.C. GENE SEGMENTS

Ig Polypeptides Are Encoded by Multiple Gene Segments

Heavy chain isotypes are generated by a second DNA rearrangement:

CLASS SWITCH RECOMBINATION (CSR)

Figure 4-18

Figure 4-17

Figure 4-19mRNASplicing

DNA rearrangement: CSR

Figure 4-20IgM and IgD Are Generated from a Single PrimaryTranscript by DIFFERENTIAL mRNA POLY A/SPLICING

mRNAsencoding bothmembrane andsecreted formsof mu heavychain are gen-erated from asingle primarytranscript bydifferential splicing and polyadenylation

Membrane vs. Secreted Mu

Figure 4-21

CSR Involves DNA Deletion and Loss

“Germline” (I region) Transcripts Are Necessary For Isotype Switch Recombination

Figure 9-7

T cell secretes cytokines

Specific I region transcription

Isotype switch recombination to specific CH gene segment

TGF

ISCRNA

Cut and joinS and SDNA

VDJC mRNA

IgA

V(D)J Recombination CSR

Join in exon Join in intron

RAGs required RAGs Not required AID is required

Repair enzymes Repair enzymes

Generates diversity Changes isotypeAg specificity Ag elimination

Regulated by T cell signalsRandom

1. Humans with mutations in gene products required forV(D)J recombination are immunodeficient:

RAG Various SCIDs, including Omenn’s syndrome

Artemis Radio-sensitive SCID

Ligase IV SCID with developmental deficiency

2. Humans with mutations affecting CSR have hyper IgM

AID mutations and other mutations