INTERPRETING THE RESULTS OF LUMINEX-SINGLE ANTIGEN BEADS ASSAY

Anti-human leukocyte antigen (HLA) antibodies are produced by alloimmunization resulting from transfusions, pregnancies or transplants. The recent introduction of the Luminex-single antigen (LSA) beads (a solid phase assay which consists of microbeads coated with recombinant HLA antigens) greatly enhanced anti-body characterization of patients on transplant waiting lists. Using this assay, many authors reported the presence of HLA antibodies in patients who have never been alloimmunized. These findings might be due to denatured HLA molecules coated to some beads that could give rise to positive results of unknown clinical significance. Otherwise, the detected HLA antibodies might be produced to cross-reactive epitopes found in microorganismsor ingested proteins. The aim of the study was to characterize the 'kind' of LSA-detected antibodies, using the new iBeads assay (microbeads with a reduced amount of denatured HLA class I antigens), in serum samples from 30 HLA class I positive patients: 20 patients were non-alloimmunized and the remaining 10 had received sensitizing events that determined production of antibodies with low fluorescence intensity values. Eight of the 20 non-alloimmunized patients showed iBeads negative results, that is to say that these patients had produced antibodies specific for denatured HLA molecules. Twelve non-alloimmunized patients showed iBeads positive results that might be related to an immune response to epitopes shared between HLA and other proteins. Four of the 10 immunized patients showed iBeads negative results and consequently they could not be considered as 'HLA alloimmunized patients', 6 immunized patients had HLA antibodies that reacted positively with iBeads. In conclusion our findings demonstrated that LSA assay was able to detect not only different 'kinds' of HLA reactive antibodies such as alloantibodies, but also antibodies specific for denatured HLA molecules or for cross-reactive epitopes whose clinical relevance has to be investigated. Finally, it is mandatory to discriminate between these different LSA-detected antibodies to define the real immunologic risk of a potential organ transplant.