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The "anti-HBc alone" is a frequent serological finding in clinical laboratories, making it difficult to determine whether the HBV infection has resolved. The objectives of this study were to investigate the prevalence of anti-HBc alone and HBV DNA detection (occult HBV infection) among anti-HBc alone, and to describe the demographic and clinical characteristics of anti-HBc alone. A total of 17,677 sera referred from the Health Promotion Center (HPC group, 4,014 sera) as well as all the hospital clinical departments (Patient group, 13,663 sera) were tested for HBs Ag, anti-HBc, and anti-HBs. HBV DNA test using real-time PCR was performed on 230 anti-HBc alone. The prevalence of anti-HBc alone was 8.9%, significantly higher in the Patient group than in the HPC group. The prevalence of anti-HBc was higher in men than women and was increased with age. Very low levels of HBV DNA were found in only 4 (1.7%) out of 230 subjects with anti-HBc alone. They were patients with conditions unrelated to chronic liver disease. Considering the high prevalence of anti-HBc alone, the frequency of occult HBV infection among anti-HBc alone was unexpectedly low. In addition, HBV viral load was low in these patients. Further studies are required to determine the clinical significance and infectivity of anti-HBc alone, in conjunction with very low levels of HBV DNA and to standardize the detection methodology for both anti-HBc alone and HBV DNA.

The MLL gene is interrupted and fused to a number of partner genes as a result of chromosomal translocations in human leukemias. MLL is a very large protein with a unique domain structure and large regions of homology to Drosophila trx. To de®ne the key structural and functional domains of the MLL protein in vertebrates, we have cloned the genomic region encoding an MLLlike gene in the compact model vertebrate genome of Fugu rubripes. While the similarity between the mouse and human MLL proteins is very high, a lower overall similarity is present between the Fugu and mammalian proteins. Several new highly conserved regions were identi®ed in the portion of the protein included in the MLL leukemia-associated fusion proteins. The conserved nature of regions of similarity between vertebrate forms of MLL and the Drosophila TRX proteins, as well as other domains previously suggested to have a functional role in MLL (including the AT hooks and the DNA methyltransferase domain), was also observed. Therefore, strong evolutionary constraints limited sequence divergence within these domains. The information derived from this comparative analysis will form the basis for the functional study of the MLL protein, particularly as it relates to human leukemogenesis.

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