Evolution of HL-A and other major histocompatibility systems.
The HL-A region is a complex highly polymorphic system containing many genes with interrelated functions on the cell surface. Population data suggest the action of natural selection, perhaps via linked immune-response genes. Major histocompatibility systems, such as HL-A, are presumed to have their counterparts in at least all mammalian species. The complexity of the region suggests evolution by gene duplication. The integrity of the region may even extend to the human equivalent of the complex T locus of the mouse.