Appearance of Natural Antibodies in Young Rabbits

NATURALLY occurring antibodies to antigens of erythro-cytes, tissues such as liver, and microbes are invariably detectable in the serum of fully grown animals but are not found in the serum of the new-born. Whether these antibodies arise as a result of normal physiological maturation or as a result of inapparent immunization has puzzled immunologists for many years. There is evidence that the blood group and microbial antibodies may be formed as a response to ingested antigens, since their production has been prevented in some cases by rearing the animals in a germ-free environment. Germ-free chicks, for example, promptly developed antibodies to blood group B antigen after the oral administration of Escherichia coli 086, an organism with blood group B antigenic determinants 1 . The phenomenon of naturally occurring complement-fixing serum substances reactive with extracts of mammalian tissue, including an animal's own tissue, is not readily explained 2,3 . It is possible that these substances, which are serum globulins, are not antibodies formed in response to antigenic stimulation. When combined with tissue for which they have an affinity, they may conceivably be aggregated and thereby fix complement 4 .