Abstract
BACKGROUND
In contrast to evidences of Ig H chain receptor editing in transformed cell lines and transgenic mouse models, there has been no direct evidence that this phenomenon occurs in human developing B cells.
METHODS
V(H)DJ(H) rearrangements were obtained from genomic DNA of individual IgM- B cells from liver and IgM+B cells from bone marrow of 18 wk of gestation human fetus by PCR amplification and direct sequencing.
RESULTS
We found three examples of H chain receptor editing from IgM+ and IgM+human fetal B cells. Two types of V(H) replacements were identified. The first involved V(H) hybrid formation, in which part of a V(H) gene from the initial VDJ rearrangement is replaced by part of an upstream V(H) gene at the site of cryptic RSS. The second involved a gene conversion like replacement of CDR2, in which another V(H) gene donated a portion of its CDR2 sequence to the initial VDJ rearrangement.