Paucity of V-D-D-J Rearrangements and VH Replacement Events in Lupus Prone and Nonautoimmune TdT−/− and TdT+/+ Mice

Abstract

CDR3 regions containing two D segments, or containing the footprints of VH replacement events, have been reported in both mice and humans. However, the 12–23 bp rule for V(D)J recombination predicts that D-D rearrangements, which would occur between 2 recombination signal sequences (RSSs) with 12-bp spacers, should be extremely disfavored, and the cryptic RSS used for VH replacement is very inefficient. We have previously shown that newborn mice, which lack TdT due to the late onset of its expression, do not contain any CDR3 with D-D rearrangements. In the present study, we test our hypothesis that most D-D rearrangements are due to fortuitous matching of the second apparent D segment by TdT-introduced N nucleotides. We analyzed 518 sequences from adult MRL/lpr- and C57BL/6 TdT-deficient B cell precursors and found only two examples of CDR3 with D-D rearrangements and one example of a potential VH replacement event. We examined rearrangements from pre-B cells, marginal zone B cells, and follicular B cells from mice congenic for the Lbw5 (Sle3/5) lupus susceptibility loci and from other strains of mice and found very few examples of CDR3 with D-D rearrangements. We assayed B progenitor cells, and cells enriched for receptor editing, for DNA breaks at the “cryptic heptamer” but such breaks were rare. We conclude that many examples of apparent D-D rearrangements in the mouse are likely due to N additions that fortuitously match short stretches of D genes and that D-D rearrangements and VH replacement are rare occurrences in the mouse.

V(D)J Recombinase-Mediated TCR β Locus Gene Usage and Coding Joint Processing in Peripheral T Cells during Perinatal and Pediatric Development

“…We also observed an unusual TCRb coding joint that used both Db gene segments, which appears, at best, to be a very rare event at both the TCRb locus, where the D segments are separated, and at IgH coding joints (31)(32)(33)(34). We are aware of one similar event described at the TCRb locus isolated from a 39-y-old healthy female (30).…”

Abrogation of Lupus Nephritis in Activation-Induced Deaminase-Deficient MRL/lpr Mice

“…B cell-deficient-MRL/lpr mice failed to develop glomerulonephritis (22)(23)(24). Also important is a diverse lymphocyte repertoire, because MRL/lpr mice lacking terminal deoxynucleotidyl transferase, an enzyme that adds nucleotides to the V(D)J segments during recombination, have decreased glomerular disease (25)(26)(27)(28)(29). However, how B cells contribute to lupus nephritis might be more complicated than previously appreciated.…”

Animal Models of Molecular Pathology

“…This was confirmed in in vitro experiments using another BCR model expressed in MRL mice. 280 Therefore, the 3H9 model has identified multiple aspects of the dysregulation in B-cell tolerance toward an SLE-relevant self-Ag that occurs in a predisposed lupus background.…”