1. Ig Polypeptides Are Encoded by Multiple Gene Segments LIGHT CHAIN
Light Chain POLYPEPTIDE
Gene Segments
Light Chain GENE SEGMENTS
HEAVY CHAIN V a r i a b l e C n t o s a t
H.C.POLYPEPTIDE
Polypeptide V D J C C C
Gene Segments H 1 H 2 H 3
H.C. GENE SEGMENTS

2. A Prototype Ig Gene: Murine Kappa
About 10
4 J Gene
1 C
Gene k V
gene segments
Segment s
Segmen t k
Multiple V gene segments, distant from J and C
A few J gene segments
One C gene segment

3. Heavy Chain Gene Organization
Murine Ig
Heavy Chain Gene Organization
~ 120 V
4 Js
8 Constant Gene Segments
~20 Ds
Gene Segments C m C C 2b d C g 3 C g 1 g C 2a C g e C a L V H C m 1 C m 2 C m 3 C m
4/S C m M

4. Figure 4-4
Human Ig Loci

5. TCR Alpha and Beta Loci

6. TCR Delta and Gamma Loci

7. IMMUNOGLOBULIN GENES UNDERGO TWO DNA REARRANGEMENTS
V(D)J Recombination: both light and heavy chains
Class switch recombination: heavy chains only

8. DNA Rearrangement RemovesSequences Between V, D and J Segments
RNA Splicing Removes Sequences Between J and C Segments
Figure 4-2
DNA
RNA

9. Figure 4-6 V(D)J recombination involves DELETION of DNA between
V, D and J coding
segments.
The deleted DNA is
LOST from the cell
because it is not
replicated.

10. Figure 4-5 Recombination Signal Sequences (RSSs)
Flank Rearranging Gene Segments
Figure 4-5
RSS=heptamer, spacer
and nonamer
7bp
9bp
12/23 bp

11. Figure 4-7 #1: #2: Lymphocyte- Constitutive Specific Initiation of
V(D)J
rearrangement : RAG-
dependent
cleavage
Resolution
of cleavage
products:
DNA non-
homologous
end-joining
machinery

12. Figure 4-8 Addition of Bases at V-D-J Junctions:
An Important Source of Diversity
Figure 4-8

13. Figure 7-18

14. CONSEQUENCES OF V(D)J RECOMBINATION
Combinatorial diversity: # of possible combinations
is the product of the # of recombining segments
i.e. for mouse h.c.: 120x20x4=104
2. Junctional diversity at CDR3
Deletion of bases at junctions
N region additions at junctions
P region additions at junctions
3. Activates transcription of the rearranged gene
Juxtaposition of intronic enhancers with V region
promoters.
4. Allows receptor editing to alter potentially self-reactive
antibodies

15. Ig Polypeptides Are Encoded by Multiple Gene Segments LIGHT CHAIN
Light Chain POLYPEPTIDE
Gene Segments
Light Chain GENE SEGMENTS
HEAVY CHAIN V a r i a b l e C n t o s a t
H.C.POLYPEPTIDE
Polypeptide V D J C C C
Gene Segments H 1 H 2 H 3
H.C. GENE SEGMENTS

16. Heavy chain isotypes are generated by
a second DNA rearrangement:
CLASS SWITCH RECOMBINATION (CSR)

17. Figure 4-18

18. Figure 4-17

19. Figure 4-19
mRNA
Splicing
DNA rearrangement: CSR

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

21. Membrane vs. Secreted Mu
mRNAs
encoding both
membrane and
secreted forms
of mu heavy
chain are gen-
erated from a
single primary
transcript by
differential
splicing and
polyadenylation

22. CSR Involves DNA Deletion and Loss
Figure 4-21

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

24. Figure 9-7

25. T cell secretes cytokines TGF
Specific I region transcription
IaSaCaRNA
Isotype switch recombination to
specific CH gene segment
Cut and join
Sm and SaDNA
VDJCa mRNA
IgA

26. 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 isotype
Ag specificity Ag elimination
Regulated by T cell
signals
Random

27. 1. Humans with mutations in gene products required for
V(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