C H A P T E R 3 5 , F I G U R E 18
B-cell clonal selection. Antigen binding to the surface Ig (monomeric IgM and IgD)
receptors occurs only to the B-cell clone that recognizes a particular epitope on the antigen (Figure 35-1).
5 ’
-
E
]
—
3
’
t
5
’ -
5
>®—H - B - 3’
Exon/lntron
Rearrangement
Transcription
Splicing
Translation
5’ -SD-®—0-S -S — 3’
I
Ï5 E
3’
Germline
DNA
3’
B-cell DNA
3’
1° RNA
Transcript
0
NH,
COOH
DO
mRNA
(Mature)
Nascent light
chain
Domain Exons
C H A P T E R 3 5 , F I G U R E 1 9
Immunoglobulin light chain gene structure and gene processing. Germline
immunoglobulin genes consist of exons selected during differentiation to generate the mature mRNA that is translated
to give the immunoglobulin chain that recognizes a single specific epitope. Exons (>100) code for the first -95 amino
acid residues, the VL regions of the
k
and X chains. J (junction) exons code for the next -15 amino acid residues.
Separate exons exist for the CL regions of the
k
and X chains. Diversity in the CDR3 region of the VL chain arises
from the various combinations of the 5 J exons that can occur with the -100 VL exons. The excised DNA of the
germline is degraded, leaving a specific B-cell DNA that “defines” the particular B-cell clone. The primary RNA tran-
script that is formed is spliced such that the primary transcript becomes a mature mRNA that is translated into a spe-
cific Ig light chain.
