Detection of HLA IgG antibodies by two enzyme-linked immunoassays, solubilized HLA class I and PRA-STAT - Comparison with the AHG PRA

HLA class I-directed IgG antibodies have traditionally been detected with a complement-dependent lymphocytotoxicity (CDL) technique, We have evaluated two solid-phase enzyme-linked immunoassays (FIA) and compared them with the CDL antihuman globulin (AHG) dithiothreitol-treated (DTT) PRA in their ability to discriminate between the presence or absence of HLA class I-directed IgG antibodies in serum from patients awaiting transplantation. The EIA were: (1) an EIA that uses solubilized HLA class I antigens (sHLA-I) isolated from a 240-member platelet donor pool, and (2) the PRA-STAT ELISA kit. For the first comparison, we used 691 serum samples from 272 patients taken before they had been transplanted, The data show a significant (P<0.0001) linear correlation (r=0.77 between the AHG DTT PRA and the sHLA EIA. They also demonstrate that the mean sHLA-I EIA ratio significantly increases (P<0.01) above background levels with each stepwise increase in AHG DTT PRA level. Discordant results were 1.0% (7/691) for sHLA-I EIA(+) PRA(-) and 6.3% (44/691) for PRA(+) sHLA-I EIA(-). However, a lower correlation was noted between the AHC: DTT PRA and the PRA-STATT(TM) (Nextran) PRA results (n=230; r=0.42). The sHLA-I EIA is able to determine whether or not HLA Class I IgG antibodies are present in serum from transplant candidates and is an appropriate adjunct to the traditional CDL PRA assay, whereas the PRA-STAT is not.