新生儿有限的免疫球蛋白重链可变区基因多样性

Limited Diversity of the Immunoglobulin Heavy Chain Variable Region Gene in Neonates

目的 比较正常新生儿和健康成人免疫球蛋白重链可变区 (IgH)基因的可变区基因片段 (VH)、多样化基因片段 (D)和连接区基因片段 (JH)的使用 ,VH 上的突变 ,N区 -D基因片段 -N区 (NDN)长度以及开放性阅读框 (ORF)等情况 ,探讨新生儿IgH重排基因特征及其多样性。 方法 10例正常足月新生儿脐血和 8例健康成人外周血DNA被抽提 ,IgH基因被扩增、克隆和测序。结果 ①对于VH 和D的使用 ,新生儿和成人相似 ,即VH3使用率最高、VH7使用率最低 ,D2被优先使用 ;而对于JH 的使用 ,新生儿和成人不同 ,即新生儿偏倚使用JH3 ,成人使用JH 则趋向随机化。②新生儿和成人IgH重排基因的VH-D -JH 连接点处均有N区插入 ,但新生儿的NDN长度 [(2 1.2± 5 .7)bp]短于成人 [(2 6 .6± 6 .5 )bp]。③新生儿的IgH基因序列无碱基缺失而成人存在 ;新生儿IgH基因少有体突变 (2 9.2 % ) ,而 77.1%的成人IgH基因存在体突变。④新生儿有ORF的IgH基因序列为91.7% ,而成人为 10 0 %。结论 正常新生儿和健康成人的IgH重排基因序列存在着异型性。新生儿的IgH重排基因已处于活化状态 ,但由于VH,D和JH 的偏倚使用 ,NDN短以及少有突变 ,其多样性有限。

Objective To compare the features and diversity of the immunoglobulin heavy chain variable region (IgH) gene in neonates and adults. Methods DNA was extracted from the cord blood of 10 full term neonates and from the peripheral blood of 8 adults. The IgH gene was amplified using the nested PCR technique, and then cloned and sequenced. Results The usage of variable (VH) and diversity (D) segments in neonates was similar to that in adults: V H3 and D2 usage were preferred, while V H7 was incidentally used. With respect to the usage of joining segments (J H), there was a bias towards J H3 in neonates, while there was a tendency to randomize in adults. N region inserts at the V H-D-J H point of rearranged IgH existed in both neonates and adults. The N region-D gene-N region (NDN) length in neonates was ( 21.2 ± 5.7 ) base pairs (bp), which was shorter than that in adults [( 26.6 ± 6.5 ) bp]. There was no base loss in the neonatal IgH gene, whereas there was some loss in adults. Neonates had a much lower somatic mutation rate ( 29.2% ) than adults ( 77.1% ). Open reading frames (ORF) occurred in the rearranged IgH gene of neonates and adults at the ratio of 91.7% and 100%, respectively. Conclusions Differences in IgH gene rearrangement exist between neonates and adults. Rearranged IgH of neonates is in an activated condition, but its diversity is limited secondary to preferential selection of VH, D and JH segments, short NDN and decreased somatic mutation rate.[