Characterisation of antibody populations in renal dialysis patients : their role in renal transplant outcome

The relevance of a positive crossmatch in renal transplantation is controversial. Factors which may influence the relationship between recipient antibody sensitization and transplant outcome include; the antibody class and specificity, the time interval between the positive crossmatch and transplantation and whether the transplant is a first graft or a regraft. In highly sensitized patients the clinical relevance of a positive crossmatch against a particular donor is difficult to determine because it may be due to damaging (presumed antiHLA) and/or non-damaging (presumed non-HLA) antibodies. An in vitro assay has been developed which can reliably define the specificity of donor reactive antibodies even in complex mixtures. This technique was applied to define the immunoglobulin class and specificity of antibodies present in a series of positive crossmatch transplants. The clinical relevance of sensitization to HLA class I, DR, DQ and non-HLA was examined and a correlation sought with graft survival. The results showed good primary and regraft survival in the presence of peak positive and current positive crossmatches caused by IgM non-HLA antibodies. There was acceptable primary and regraft survival with peak positive-current negative crossmatches due to IgM HLA class I, but not with IgG antibodies. A positive B cell crossmatch caused by HLA antibodies was associated with good primary but poor regraft survival. These findings may be applied prospectively to select kidney donor and recipient pairs Who, despite a positive crossmatch, can be transplanted with a high probability of success. The target molecule of the commonest non-HLA antibody has remained a mystery for over 15 years. This question was investigated by the production and characterisation of human monoclonal antibodies from a renal dialysis patient by the generation of a mouse/human heterohybridoma. The resulting antibodies are of the IgM class with reaction profiles identical to those found in renal dialysis patients. Screening against panels of cells demonstrated that identical reactivity patterns could be generated at a different dilution for each MAb. This implies that the apparently different specificities are explained by differential target cell sensitivity. Reactivity profiles in fluorescence binding assays showed that this target cell sensitivity is dictated not by antigen density alone but also by antibody/antigen affinity. The results from enzyme treatment of target cells and from lectin inhibition studies show that the antibodies are polyreactive and capable of binding sialic acid dependent epitopes and other negatively charged cell surface molecules.