APPENDIX 16 Studies on Australia Antigen in Micronesian Populations Baruch S. Blumberg, The Institute for Cancer Research, Philadelphia, Pa. Australia antigen is a serum protein first detected in the serum of Australian aborigines, using an antiserum developed in a hemophilia patient who had received a large number of transfusions.(1) The distribution of this trait has now been studied in more than 50 human populations. (See Table 1.) It was very rare in normal United States populations (none in 1,500 sera) but fairly common (3-6%) in sera collected from Marshall Islanders, Australian aborigines, Vietnamese, Filipinos, Polynesians, and other Southeast Asian populations. It is less common in Mediteranean populations and is extremely rare in Northern European populations and in most autochthonous New World populations. In addition to the relevance of this trait to studies on cancer (see below), it is of interest in anthropological studies of human populations. Australia antigen migrates as an alpha protein on immuno-electrophoresis. The precipitin band which forms between the hemophilia antiserum and the serum containing Australia antigen stains faintly With Sudan black, indicating that the protein contains some lipid. Australia antigen has a specific gravity between 1.063 and 1.30, that is, it is more dense than low density lipoprotein but less so than most other serum proteins. It appears in the first peak in Sephadex G200 column chromotography, indicating that it is a high molecular weight serum protein. It is found in the fifth and sixth peaks on DEAE column chromotography. The protein can be isolated by a combination of Sephadex chromotography and high speed ultracentrifugation. The antibody in the hemophilia serum which reacts with the Australia antigen travels in the I G (7S) gamma globulin fraction. (2) 8 Antisera against the protein havebeen produced by the immunization of rabbits with serum containing Australia antigen and the subsequent absorption of the antiserum with the sera of normal persons. (3 In order to initiate studies on the inheritance of Australia antigen, it was necessary to determine if the trait was persistent over the course of weeks, months, or years. Sera collected from the population of Rongelap Atoll over the course of up to eight years were available. Samples from a total of 300 Micronesians from Rongelap were collected from the period 1958 to 1965. Of these, serial samples were available from 250 individuals. Of the latter, 237 were consistently negative, eleven were consistently positive and two were inconsistent. only one of multiple sera. In each case, the inconsistency was apparent in (See Figure 1.) Family studies were undertaken on a total of 36 families, including 5 families from Rongelap. The results were consistent with the hypothesis that individuals homozygous for a gene termed Aul (genotype Aut /Aul) have detectable Australia antigen in their blood (phenotype Au 1 ). Individuals 150