Immunoglobulins recognize foreign antigens and initiate immune responses such as phagocytosis and the complement system. Each immunoglobulin molecule consists of two identical heavy chains and two identical light chains. This region represents the germline organization of the heavy chain locus. The locus includes V (variable), D (diversity), J (joining), and C (constant) segments. During B cell development, a recombination event at the DNA level joins a single D segment with a J segment; this partially rearranged D-J gene is then joined to a V segment. The rearranged V-D-J is then transcribed with the IGHM constant region; this transcript encodes a mu heavy chain. Later in development B cells generate V-D-J-Cmu-Cdelta pre-messenger RNA, which is alternatively spliced to encode either a mu or a delta heavy chain. Mature B cells in the lymph nodes undergo switch recombination, so that the V-D-J gene is brought in proximity to one of the IGHG, IGHA, or IGHE genes and each cell expresses either the gamma, alpha, or epsilon heavy chain. Recombination of many different V segments with several J segments provides a wide range of antigen recognition. Additional diversity is attained by junctional diversity, resulting from the random additional of nucleotides by terminal deoxynucleotidyltransferase, and by somatic hypermutation, which occurs during B cell maturation in the spleen and lymph nodes. Due to polymorphism, the numbers of functional V, J, and D genes differ among individuals and some V, D, J, and C segments may be pseudogenes. [provided by RefSeq, Oct 2013]

[中文简述(自动翻译):]  免疫球蛋白识别外来抗原，并启动免疫反应，如吞噬作用和补体系统。每个免疫球蛋白分子包含两个相同的重链和两条相同的轻链组成。这个区域表示的重链基因座的种系组织。轨迹包括V（可变的），D（多样性），J（连接），和C（常数）段。在B细胞发育，在DNA水平上一个重组事件加入与J区段的单个D区段;那么这部分重排D-J基因加入到一个V形段。重排的V-D-J的然后用IGHM恒定区转录;这份成绩单编码亩重链。以后开发的B细胞产生V-D-J-CMU-Cdelta前信使RNA，这是选择性剪接来编码任一亩或增量重链。成熟B细胞在淋巴结经受转换重组，从而使V-D-J基因被带到接近的IGHG，IGHA或IGHE基因之一并且每个细胞表达任一γ，α或ε重链。有几个J片段许多个别V段的重组提供了多种抗原识别。额外的多样性是由连接多样性达到，从随机附加由终端脱氧核苷酸转移酶的核苷酸所得，并通过体细胞突变，这在脾和淋巴结B细胞成熟过程中发生。由于多态性，官能Ⅴ的数，J和D基因的个体和一些V，D，J之间不同，和C链段可以是假基因。 [由RefSeq的，2013年10月提供]

IGH基因在不同组织中的表达：    [UniProt]

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