“…However, by the time the in utero gestational period was over, the D segment use shifted to the 5ЈV H proximal end of the locus, particularly increasing the frequencies of D2-2, D3-3, D3-10, and D6 -13 in full-term neonates and adults. Moreover, the finding that in the fetus the two most J H proximal D segments, D1-26 and D7-27, preferentially rearranged with J H 2 and J H 3 further supports the hypothesis that proximity of the D segment and J H pairing is favored in the V H DJ H rearrangement process in B lineage cells of the fetus (32,33). Even though reports suggested that the reason for fetal D7-27 pairing with 5ЈJ H segments was based on the D segment size (12,19), we consider this unlikely because other small D segments, such as the ones in the D4 family, were not frequently used, whereas the relatively long D1-26, which is the second most J H proximal D segment, also paired preferentially with 5ЈJ H segments.…”