B-cell receptor cross-linking delays activation-induced cytidine deaminase induction and inhibits class-switch recombination to IgE.
BACKGROUND
During differentiation, B cells receive signals by antigen through the B-cell receptor (BCR) and signals that induce isotype switching.


OBJECTIVE
We sought to investigate the effects of BCR ligation on isotype switching.


METHODS
Naive B cells from BALB/c mice were stimulated with LPS plus IL-4 alone or plus anti-IgM (0.1-10 mug/mL). IgE and IgG1 levels in supernatants were measured by means of ELISA on day 6. Cmu or Cvarepsilon germline transcripts, activation-induced cytidine deaminase (AID), and Imu-Cvarepsilon postswitch transcripts were measured by means of RT-PCR. Deletional switch recombination was assessed by means of digestion circularization PCR of Smu-Svarepsilon products.


RESULTS
BCR cross-linking inhibited IgE and IgG1 switching in a dose-dependent fashion. This was not due to inhibition of proliferation, increased apoptosis, or cell death. BCR cross-linking had no effect on Cmu or Cvarepsilon germline transcripts but suppressed the generation of Smu-Svarepsilon switch products and Imu-Cvarepsilon postswitch transcripts and caused a delay in the expression of AID mRNA, with decreased expression on days 2 and 3 after stimulation. Concomitantly, the number of DNA repair foci at the IgH locus on day 3 was significantly decreased. AID expression and activity became normal on day 4, but isotype switching remained profoundly diminished 8 days after stimulation.


CONCLUSIONS
BCR cross-linking delays AID expression. This might interfere with class-switch recombination by disrupting the temporal coordination of signals that lead to class-switch recombination.
Jabara
Haifa H
HH
Division of Immunology, Children's Hospital, Boston, MA 02115, USA.
Chaudhuri
Jayanta
J
Dutt
Shilpee
S
Dedeoglu
Fatma
F
Weng
Yu
Y
Murphy
Michael M
MM
Franco
Sonia
S
Alt
Fredrick W
FW
Manis
John
J
Geha
Raif S
RS
D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism; D002478:Cells, Cultured; D003564:Cytidine Deaminase / Q000096:biosynthesis*; D004790:Enzyme Induction; D017578:Immunoglobulin Class Switching / Q000235:genetics* / Q000276:immunology*; D007073:Immunoglobulin E / Q000096:biosynthesis*; D007074:Immunoglobulin G / Q000096:biosynthesis; D051379:Mice; D008807:Mice, Inbred BALB C; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D011995:Recombination, Genetic; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D007074:Immunoglobulin G; D011947:Receptors, Antigen, B-Cell; D007073:Immunoglobulin E; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase