Among members of the Ig superfamily (IgSF), antigen receptors have the unique capacity to rearrange their variable domains, thereby creating an extensive repertoire for antigen recognition. It is assumed that antigen receptors evolved from a non-rearranging IgSF member by insertion of a transposable element. Although the nature of this predecessor is unknown, two multigene families of innate immune receptors that bear a close structural resemblance to antigen receptor chains have been identified in mammals and bony fish, respectively: signal-regulatory proteins (SIRPs) and novel immune-type receptors (NITRs). Members of both families encode V-set Ig domains with a typical antigen receptor-like joining (J) motif and possess the potential to signal through immunoreceptor tyrosine-based inhibition motifs (ITIMs) or immunoreceptor tyrosine-based activation motifs (ITAMs). By analogy to the T-cell receptor (TCR) and certain innate receptors [e.g. killer cell inhibitory receptors (KIRs)] that recognize MHC molecules, SIRP members regulate immune function by interaction with broadly expressed 'self' ligands. We propose the existence of an evolutionary and functional link between innate and adaptive immune receptors that sheds light on the nature of the antigen receptor predecessor(s).

中文翻译：

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关于适应性免疫的起源：先天性免疫受体加入了这个故事。

在Ig超家族（IgSF）的成员中，抗原受体具有独特的能力来重新排列其可变域，从而为抗原识别创建了广泛的库。假定抗原受体是通过插入可转座因子从非重排的IgSF成员进化而来的。尽管此前身的性质尚不清楚，但已在哺乳动物和骨鱼中分别鉴定出两个与抗原受体链具有相似结构的先天免疫受体的多基因家族：信号调节蛋白（SIRP）和新型免疫类型受体。 （NITR）。这两个家族的成员都编码具有典型抗原受体样连接（J）基序的V-set Ig域，并且具有通过基于免疫受体酪氨酸的抑制基序（ITIM）或基于免疫受体酪氨酸的激活基序（ITAM）发出信号的潜力。与识别MHC分子的T细胞受体（TCR）和某些先天受体（例如，杀伤细胞抑制受体（KIR））类似，SIRP成员通过与广泛表达的“自身”配体相互作用来调节免疫功能。我们提出先天性和适应性免疫受体之间存在进化和功能上的联系，这阐明了抗原受体前身的性质。SIRP成员通过与广泛表达的“自我”配体相互作用来调节免疫功能。我们提出先天性和适应性免疫受体之间存在进化和功能上的联系，这阐明了抗原受体前身的性质。SIRP成员通过与广泛表达的“自我”配体相互作用来调节免疫功能。我们提出先天性和适应性免疫受体之间存在进化和功能上的联系，这阐明了抗原受体前身的性质。