Allorecognition in biological systems

Colonial marine organisms of several phyla show the capacity for allogeneic recognition and response. In the colonial tunicate Botryllus, colony fusibility characteristics are determined by a single Mendelian locus with multiple co-dominant alleles. Since this genetic region may also control certain differentiation steps and sperm-egg recognitions at fertilization, it is possible that the physical and functional association of the T and H-2 complexes in the mouse may reflect an ancient association between the primitive precursors to these genes. The presence of histocompatibility systems in both solitary and colonial marine organisms suggests that genes governing histocompatibility may already be employed at these levels in recognition and response to parasitic bacteria and viruses.