Elucidation of the molecular evolution of MHC family and the establishment of the acquired immune system

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The MHC family with the characteristic structure has various important biological functions including the peptide-presentation to T cells by the classical MHC molecules. However, the molecular evolution of the MHC family has not been clarified yet. To further understand the origin and the diversity of the MHC family and the establishment of the acquired immune system, we have been investigating the MHC-like molecules from primitive animals such as the cartilaginous fish. The MHC family can be classified into two classes, the class I and the class II, based on amino acid sequences and structural characteristics. Previously, we demonstrated that the MHC family molecules exist in the most primitive jawed vertebrates, the cartilaginous fish, and that the two classes has already been established at the level of fish. Further, we reported the generality of the mechanisms that create exceptionally high polymorphism of the classical MHC molecules, which is the basis of the allograft rejection. In relation to the establishment of the two classes, we recently clarified a novel gene that possesses the characteristics of both classes, and revealed that it belongs to a very unique linkage group. In this study, we also analyzed the MHC-related genes from the standpoint of the evolution of the MHC region in the genome.