Four TAP1 alleles (0101, 0201, 0301 and 0401), and four TAP2 alleles (0101, 0102, 0103 and 0201) have been already identified in the Caucasian population. We investigated TAP1 and TAP2 polymorphisms in 106 healthy Japanese by PCR-low ionic strength single stranded conformation polymorphism (PCR-LIS-SSCP). Three of four TAP1 and all known TAP2 alleles were identified in these suhjects, and the allele frequencies of TAP1 were similar between the Japanese and the Caucasian populations, although those of TAP2 were different. Moreover, we found a new sequence variation at codon 577 (ATG→GTG:Met→Val) in the ATP-binding domain of the TAP2 gene. This variation was found in 12.4% of healthy Japanese (allele frequency: 6.6%), exhibited a strong linkage disequilibrium with DRB1* 0803-DQB1* 0601 and leaded to recognition of a new TAP2 allele, TAP2* Bky2 (allele frequency: 5. 1%).

A serological subtype of HLA-A locus antigen, tentatively called HLA-A9HH, was identified in the Japanese population. A9HH showed short reaction patterns of a series to anti-A9 sera and reacted with some anti-A2 sera. Nucleotide sequence of full-length cDNA for A9HH was determined. The obtained sequence was compared with those of other A24 alleles reported to date, and it was revealed that this new sequence was identical with that of A* 2408 except at position 8 in exon 2. However, subsequently the nucleotide sequence of A* 2408 was revised by the original investigators and this revised sequence was found to be identical to that of A9HH. The nucleotide sequence of the allele for A9HH was identical to that of A* 2402 except for three nucleotides in exon 2. These three nucleotide changes cause three amino acid changes. Two of the three amino acids are shared by all the reported A2 alleles. These sequencing results of the allele for A9HH were consistent with the serological cross-reactivity of A9HH with some anti-A2 sera. The probable haplotypes carrying A9HH (A* 2408) are A9HH-Cw1-B54 and A9HH-Cw10-B35.

We have examined 10,000 blood donors to perform the extensive study for screening the possible HLAantibodies by LCT (lymphocyte cytotoxicity test) assay. Two male donors were found to possess monospecific natural antibodies against HLA-B46 and -A2. Immunoglobulin subclass of both natural antibodies was IgM. Both donors have not experienced any blood transfusion nor transplantation. In addition, any family members of the donor positive for HLA-B46 antibody did not possess HLA-B46 antigen nor antibody. It is likely that HLA natural antibodies are more prevalent than formerly supposed. HLA antibody screening including male donors or nonpregnant female donors will provide further insights on the characteirization of HLA natural antibodies.