Cow antibodies are very unusual in having exceptionally long CDR H3 regions. The genetic basis for this length largely derives from long heavy chain diversity (DH) regions, with a single “ultralong” DH, IGHD8–2, encoding over 50 amino acids. Many bovine IGHD regions have sequence similarity but have several nucleotide repeating units that diversify their lengths. Genomically, most DH regions exist in three clusters that appear to have formed from DNA duplication events. However, the relationship between the genomic arrangement and long CDR lengths is unclear. The DH cluster containing IGHD8–2 underwent a rearrangement and deletion event in relation to the other clusters in the region corresponding to IGHD8–2, with possible fusion of two DH regions and expansion of short repeats to form the ultralong IGHD8–2 gene. Length heterogeneity within DH regions is a unique evolutionary genomic mechanism to create immune diversity, including formation of ultralong CDR H3 regions.

中文翻译：

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通过基因组重排形成超长DH区。

牛抗体在具有异常长的CDR H3区时非常不寻常。此长度的遗传基础主要来自长的重链多样性（DH）区，具有单个“超长” DH（IGHD8–2），编码超过50个氨基酸。许多牛IGHD区具有序列相似性，但具有几个核苷酸重复单元，使它们的长度多样化。从基因组上讲，大多数DH区以三个簇的形式存在，这些簇似乎是由DNA复制事件形成的。然而，基因组排列与长CDR长度之间的关系尚不清楚。包含IGHD8–2的DH簇相对于与IGHD8–2对应的区域中的其他簇发生了重排和缺失事件，可能是两个DH区融合，并且短重复序列扩展形成了超长IGHD8–2基因。