The Fetal Allograft Revisited: Does the Study of an Ancient Invertebrate Species Shed Light on the Role of Natural Killer Cells at the Maternal-Fetal Interface?

Figure 2

Botryllus schlosseri colony interactions. In the wild, colonies of B. schlosseri can become quite large, and genetic analyses reveal these colonies to be multichimeric. Interactions between genetically distinct colonies are governed by an allorecognition system controlled by the fusibility/histocompatibility locus (Fu/HC). When genetically distinct colonies contact one another, they will anastamose if one or both Fu/HC loci are recognized as self. Fusion involves the creation of a shared vasculature and common tunic. If neither Fu/HC loci are shared, rejection will occur and inflammatory lesions will develop at sites of contact. One colony will be largely resorbed after acceptable recognition and successful colony fusion, although some germ and somatic cells of the resorbed individual will persist in the survivor, creating a parasitic relationship.