Homology-directed recombination in IgH variable region genes from human neonates, infants and adults: Implications for junctional diversity

Homology-directed recombination, i.e. the preferential joining of gene segments at short sequence homologies, is found in 80% of IgH variable region genes from neonatal mice and causes a marked uniformity of their VH-DH- and DH-JH-junctions, which are predominated by one to three junctional sequences. To analyze the impact of homology-directed recombination on IgH gene diversity in humans, IgH rearrangements from fetuses and neonates (gestational age 20–42 weeks), infants (age 1–27 months) and adults were cloned and sequenced. As a marker of homology-directed recombination the VH-DH- and DH-JH-junctions were searched for nucleotides that could have been encoded by each of the two adjacent gene segments. Such overlapping sequences were rare (