Transplantation and chimera as extended self.

Transplantation can be considered as an artificial reconstitution of symbiosis called chimera, since the donor and recipient carry different DNAs. In successful transplantation, engrafted tissues and cells should be recognized as self by the immune system, as shown in external pathogens. The external milieu introduced by transplantation and infection can only be immunologically recognized as self when it forms a symbiotic relationship with somatic cell society. Immunological identity is a posteriori educated recognizing immunological self and genetic self may be ignored in self-recognition. For example, transplanted bone marrow immunocytes recognize somatic cell society which is selected previously by other immunological standards as self. Dissociation between genetic self and immunological self originates in the development and differentiation of multicellular organisms a priori, since alteration of DNA sequences is necessary in the development and differentiation of multicellular organisms and symbiosis is the essential nature of it.