Immunoglobulins (Ig) are the antigen recognition molecules of B cells. An Ig molecule is made up of 2 identical heavy chains and 2 identical light chains (see MIM 147200) joined by disulfide bonds so that each heavy chain is linked to a light chain and the 2 heavy chains are linked together. Each Ig heavy chain has an N-terminal variable (V) region containing the antigen-binding site and a C-terminal constant (C) region, encoded by an individual C region gene, that determines the isotype of the antibody and provides effector or signaling functions. The heavy chain V region is encoded by 1 each of 3 types of genes: V genes (see MIM 147070), joining (J) genes (see MIM 147010), and diversity (D) genes (see MIM 146910). The C region genes are clustered downstream of the V region genes within the heavy chain locus on chromosome 14. The IGHM gene encodes the C region of the mu heavy chain, which defines the IgM isotype. Naive B cells express the transmembrane forms of IgM and IgD (see IGHD; MIM 1471770) on their surface. During an antibody response, activated B cells can switch to the expression of individual downstream heavy chain C region genes by a process of somatic recombination known as isotype switching. In addition, secreted Ig forms that act as antibodies can be produced by alternative RNA processing of the heavy chain C region sequences. Although the membrane forms of all Ig isotypes are monomeric, secreted IgM forms pentamers, and occasionally hexamers, in plasma (summary by Janeway et al., 2005).[supplied by OMIM, Aug 2010]

[中文简述(自动翻译):]  免疫球蛋白（Ig）的是B细胞的抗原识别分子。 Ig分子是由2个相同的重链和2相同的轻链（参见MIM 147200）通过二硫键连接，使得每个重链连接到轻链和2条重链连接在一起。每个Ig重链具有包含抗原结合位点和一个C-末端恒定（C）的区域，由个人C区基因编码的N-末端可变（V）区，即决定了抗体的同种型，并提供了效应器或信令功能。重链V区是通过1编码的每个3种基因的：V基因（见MIM 147070），接合（J）的基因（见MIM 147010）和多样性（D）的基因（见MIM 146910）。 C区基因在染色体14的重链基因座内聚集的V区基因的下游的IGHM基因编码的μ重链，它定义了IgM同种型的C区。普通B细胞表达的IgM和IgD的跨膜形式（见IGHD; MIM 1471770），其表面上。期间的抗体反应，活化的B细胞可以通过被称为同种型转换体细胞重组的处理切换到个人下游重链C区的基因的表达。另外，分泌的免疫球蛋白形式充当抗体可以通过在重链C区序列替代RNA加工来制造。虽然所有的Ig同种型的膜形式是单体的，分泌的IgM形成五聚体，偶尔六聚体，在等离子体（摘要由詹韦等人，2005）。[由OMIM，2010年8月供给]

IGHM基因在不同组织中的表达：    [UniProt]

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