MONITORING OF ANTI-HLA ANTIBODIES BY LYMPHOCYTOTOXICITY AND SOLUBILIZED HLA CLASS I
          ANTIGEN ELISA.
          R Wassmuth, M-L Arnold, T Zacher, C Baum, I Doxiadis, JR Kalden.   Institute for Clinicical Immunology, University of Erlangen-Nürnberg, Erlangen, Germany, Department of Immunohematology and Blood Bank, University of Leiden, Leiden, The Netherlands.
          With the advent of ELISA-based techniques methods, our capabilities to identify HLA class I-directed IgG antibodies have improved. In comparison to the complement- dependent lymphocytotoxcity (CDC) test, ELISA testing offers a greater reproduceability, interlaboratory correlation and is less labour-intensive. Nevertheless, current commercially available formats are restricted to the detection of IgG antibodies irrespective of their ability to activate complement. Moreover, discrepancies in result between different test methods occur. Thus, the aim of the present study was to further analyze grossly discrepant test results for standard CDC testing (Lymphoscreen, Biotest, Dreieich, Germany) and the soluble HLA-based PRA-STAT test (SangStat, Menlo Park, CA, USA) observed in 28 sera. These sera were drawn from quartely antibody screenings of approx. 600 patients awaiting kidney transplantation. In 19 our of these 28 patients the CDC was positive while the PRA-STAT ELISA tested negative. Subsequent testing revealed that in 15 out of these 19 sera the QuikScreen ELISA (GTI, Brookfield, WI, USA) and the flow cytometry-based FlowPRA I Screening Test (One Lambda, Canoga Park, CA) showed a CDC-concordant positive result while 4 sera tested negative in both assays. In the second group of 9 of the 28 patients, a positive PRA-STAT ELISA and a negative CDC result was seen initially. Further analysis using antihuman globulin (AHG) CDC testing and flow cytometry (anti-CDc/anti-IgG) also failed to detect any HLA- specific antibodies. Using the QuikScreen ELISA, a CDC-concordant negative result was seen in 6 out of 9 sera while 3 sera were ELISA positive. The flow cytometry-based FlowPRA I was concordant with the CDC in all but one serum. It is concluded that discrepancies only occur in a small number of cases. However, further testing using alternative tests may be helpful to establish the presence of HLA-specific IgG antibodies.