A double determinant immunoassay for HLA class I typing using serum as an antigen source

We have applied a double determinant immunoassay (DDIA) to HLA-A2,A28, and B13 typing, using serum as an antigen source. The results obtained show a correlation of 96% (B13) and 89.1% (A2,A28) with the results obtained by conventional HLA typing. Furthermore, the results obtained were highly reproducible, since testing of 18 sera on two occasions gave concordant results with all samples tested. The variation in the content of HLA-A2 antigens in sera taken at different times from a given donor was less than 5%. A sevenfold variation was found in the serum level of HLA-A2,A28 antigens: the highest level was found in the sera from HLA-A2,A28 donors and in decreasing order in HLA-A2 homozygous, HLA-A28 homozygous, HLA-A2 heterozygous, and HLA-A28 heterozygous donors. The results of this study indicate that the DDIA is a sensitive, simple, and reproducible procedure for HLA class I typing. The DDIA offers the following advantages in comparison with the conventional lymphocytotoxic assay: it provides information not only about the expression of a given alloantigen, but also about its level; it does not require viable cells, thus facilitating retrospective studies and typing of leucopenic patients; it eliminates variability of results caused by abnormal susceptibility of target cells to complement-dependent lysis.