SUMMARY:Since its inception in the early 1960s, the serologically based complement-dependent cytotoxicity (CDC) assay has been the cornerstone technique for the detection of human leucocyte antigen (HLA) antibodies, not only in pre-transplant renal patients, but also in other forms of organ transplantation. Recently, solid phase assays have been developed and introduced for this purpose, and in particular the Flow-based bead assays such as the Luminex system. This latter assay has proved to be far more sensitive than the CDC assay and has revealed pre-sensitization in potential transplant recipients not detected by other methods of HLA antibody detection. However, the clinical implications of this increased sensitivity have not been convincingly demonstrated until recently. This technology for HLA antibody detection permits the evaluation of the clinical importance of antibodies directed at, for example, HLA-DPB1 and HLA-DQA1, which has not been possible to date. There are Luminex issues, however, requiring resolution such as the ability to distinguish between complement fixing and non-complement fixing antibodies and determination of their relative clinical significance. Luminex technology will permit a re-evaluation of the role of HLA antibodies in both early and late antibody-mediated rejection.

The significance of B-cell crossmatching in kidney transplantation is controversial. Recipients (n = 471) transplanted in a single centre from 1987 to 2005 with complete T- and B-cell crossmatch records were studied. Sera from 83 patients transplanted across a positive B-cell crossmatch, with concomitant negative T-cell crossmatch (T-B+) on either current and/or peak sera were studied using Luminex to determine presence of donor-specific antibodies (DSA). Clinical outcomes of T-B+ patients were compared with 386 T-B- patients. T-B+ predicted vascular (p = 0.01), but not cellular (p = 0.82) or glomerular (p = 0.14) rejection. IgG HLA DSA were found in 33% (n = 27) of the T-B+ patients and were associated with higher risk of any (p = 0.047), vascular (p = 0.01) or glomerular (p < 0.001) rejection at 6 months. Of 27 patients with DSA, 18/21 (86%) were the complement-fixing IgG(1) and/or IgG(3) subclass antibodies. DSA imposed a statistically significant higher risk of graft loss 5 years posttransplant (1.8 [1.0-3.3], p = 0.045). This study showed that only one-third of positive B-cell crossmatch (BXM) was caused by DSA and was associated with late graft loss. Thus, using BXM to preclude kidney transplantation may potentially disadvantage >60% of patients in whom BXM is not indicative of the presence of DSA.

These cases support the routine assessment of anti-AT1 R antibodies in kidney transplant recipients to identify subjects at risk. Further studies will need to determine optimal assessment protocol and the effectiveness of pre-emptive treatment with angiotensin receptor blockers.

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