HLA-A, B, C Typing Using Serum
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. In the DDIA, polyvinylchloride microtiter plates were coated with the anti- HLA-A2, A28 monoclonal antibody CR11-351 (MoAb)  and/or with the anti-HLA-B13 MoAb SYI . Then 25 µl serum from HLA-typed donors was added to the well, and incubated for 2 h at room temperature. After the plates had been washed three times, 125I-labeled anti-human B2m MoAb NAMB I  (2 × 105 cpm/well) was added and incubation continued for 2 h. Then the microtiter plates were washed five times and bound radioactivity was counted. The results obtained (see Table 1) were highly reproducible, since testing of 28 sera (16 positive and 12 negative) on two occasions gave concordant results with 27 of the 28 samples tested. The variation in the content of HLA-A2 antigens in sera taken from a given donor was less than 5%. On the other hand, a seven-fold variation in the level of HLA-A2, A28 antigens was found in the sera from the 55 positive donors analyzed; the highest values were found in the HLA-A2, A28 phenotype, followed in decreasing order by those in A2 homozygotes, A28 homozygotes, A2 heterozygotes, and A28 heterozygotes. No relationship between the serum level of HLA-A2, A28 antigens and the total HLA-A, B, C serum level was found. Family studies suggest that the level of HLA-A2 and A28 antigens in the serum is subject to genetic control, which does not appear to be linked to the MHC region.