“…Genetically determined resistance or susceptibility to infectious disease has been recognized for many years and has been extensively investigated in a number of experimental models (Gowen, 1948(Gowen, , 1961. The mechanisms underlying such genotypic control have been the subject of much speculation, but a realistic basis has been provided by the recent identification of specific immune response genes, which determine, in an all-or-nothing manner, the ability of an animal to respond to particular antigens (McDevitt & Benacerraf, 1969) and by the demonstration that the level of certain antibody responses is under relatively simple polygenic control (Biozzi, Stiffel, Mouton, Bouthillier & Decreusefond, 1971).…”