Why has histo-incompatibility arisen in evolution and can cause self-intolerance? Compatible/incompatible reactions following natural contacts between genetically-different (allogeneic) colonies of marine organisms have inspired the conception that self–nonself discrimination has developed to reduce invasion threats by migratory foreign germ/somatic stem cells, in extreme cases resulting in conquest of the whole body by a foreign genome. Two prominent model species for allogeneic discrimination are the marine invertebrates Hydractinia (Cnidaria) and Botryllus (Ascidiacea). In Hydractinia, self–nonself recognition is based on polymorphic surface markers encoded by two genes (alr1, alr2), with self recognition enabled by homophilic binding of identical ALR molecules. Variable expression patterns of alr alleles presumably account for the first paradigm of autoaggression in an invertebrate. In Botryllus, self–nonself recognition is controlled by a single polymorphic gene locus (BHF) with hundreds of codominantly expressed alleles. Fusion occurs when both partners share at least one BHF allele while rejection develops when no allele is shared. Molecules involved in allorecognition frequently contain immunoglobulin or Ig-like motifs, case-by-case supplemented by additional molecules enabling homophilic interaction, while the mechanisms applied to destroy allogeneic grafts or neighbors include taxon-specific tools besides common facilities of natural immunity. The review encompasses comparison with allorecognition in mammals based on MHC-polymorphism in transplantation and following feto-maternal cell trafficking.

为什么在进化过程中会出现组织不相容性并导致自我不耐受？不同基因（同种异体）海洋生物群落之间自然接触后的相容/不相容反应激发了这样一种概念，即自我非自我歧视已经发展到减少外来生殖/体干细胞的入侵威胁，在极端情况下导致征服整个身体由一个外来基因组。异体歧视的两个突出的车型品种是无脊椎动物海洋Hydractinia（刺胞动物门）和Botryllus（海鞘）。在Hydractinia 中，自我-非自我识别是基于由两个基因（alr1、 alr2)，通过相同 ALR 分子的同质结合实现自我识别。alr等位基因的可变表达模式可能是无脊椎动物自体攻击的第一个范式。在Botryllus 中，自我-非自我识别由具有数百个共显性表达的等位基因的单个多态基因位点 ( BHF )控制。当双方共享至少一个BHF时发生融合当没有等位基因共享时，会产生排斥反应。参与同种异体识别的分子通常包含免疫球蛋白或 Ig 样基序，逐案补充使同种异体相互作用的其他分子，而用于破坏同种异体移植物或邻居的机制除了自然免疫的常见设施外，还包括分类群特异性工具。该综述包括与基于移植中的 MHC 多态性和胎儿-母体细胞运输的哺乳动物同种异体识别的比较。