Anti-HLA antibodies interfere in the detection of soluble HLA class I molecules

Heart transplant rejection is routinely defined by histological evaluation of endomyocardial biopsies (EMB). As elevated levels of donor derived sHLA dsHLA can be detected in the serum of transplanted patients just before or during rejection, quantification of donor specific soluble counterparts of HLA. Class I(sHLA-I) in the serum of the recipient may be a new way for non -invasive monitoring of graft rejection. However, not all patients show an increase of dsHLA at time of rejection. A reason for this might be that ant i-donor-HLA antibodies, which are formed by the patient, form complexes wit h donor sHLA-I molecules. This masking or blocking of sHLA-I binding sites might cause false-negative results of tests detecting donor specific sHLA. Using HLA-antigen specific ELISA tests we could demonstrate that most anti- HLA antibodies block the detection of sHLA antigens in plasma, even in high dilutions of the antibody when the antibodies were not detectable in a CDC test. In general, HLA-antigen specific antibodies block the detection of s HLA molecules, while broadly-reactive antibodies, recognizing another epito pe on the molecule, do not. The implication of these findings is that more than one dsHLA allotype within one patient should be tested to monitor graf t rejection. In addition, sHLA monitoring must be combined with an HLA-anti body screening. (C) American Society for Histocompatibilicy and Immunogenet ics, 1999 Published by Elsevier Science Inc.