Incompatibilità e biodiversità

Evolution of living systems is the result of coupling and competition between catabolic reactions, degrading biological macromolecules, and anabolic reactions, increasing complexity and configurational order of biological structures. In complex animals the molecules regulating the equilibrium between the anabolic and catabolic activities of the neuroendocrineimmune system are processed and presented on the cell surface by the proteins of the Major Histocompatibility Complex (MHC). The immunisation against endogenous regulative peptides is involved in the “immunotrophic” process: a positive selection of the maternal immune system for the embryos with incompatible MHC alleles. These alleles are linked in cis or in trans with different variants of genes involved in the regulation of important metabolic activities, and therefore a physiological adaptation may be quickly transformed into adaptive changes of the genetic population structure. This mechanism counteracts the negative aspects of natural selection and maintains the biodiversity of animal populations. The hypothesised scenario is confirmed by an extensive comparison between human and bovine MHC sequences in different populations. Most of the MHC alleles of the two species have the same amminoacidic sequences produced independently by convergent evolution. Moreover we found, both in bovine and human fractal distributions of MHC polymorphism in different populations, and similar functional association between MHC alleles and metabolic and immune characteristics.