Detection of kidney reactive antibodies at crossmatch in renal transplant recipients

Serum analysis after transplant nephrectomy reveals restricted antibody specificity patterns against structurally defined HLA class I mismatches

This study deals with HLA-mismatched kidney transplants that have been removed following rejection. Sera from 27 patients were screened for HLA-specific antibodies by direct complement-dependent lymphocytotoxicity with HLA-typed cell panels. Circulating donor-specific antibodies were detected in 3 cases (11%) before and in 26 cases (97%) after allograft nephrectomy. These findings demonstrate the production of donor-specific antibodies in patients with rejected transplants, but in most cases, they were undetectable before nephrectomy, because the graft had adsorbed them. With an HLAMatchmaker-based serum analysis program, we observed restricted antibody specificity patterns against amino acid triplet-defined epitopes on donor HLA-A,B antigens. Many donor triplets were non-reactive while others were apparently recognized by antibodies. In some patients, the donor triplet specific antibodies persisted for a long time whereas in many other patients, they became undetectable after a few months. The characterization of the antibody specificity profiles of post-allograft nephrectomy sera is clinically useful in defining criteria of HLA mismatch acceptability for sensitized patients awaiting another transplant. It provides also opportunities for determining the relative immunogenicity of mismatched triplets.

Anti-endothelial cell antibodies: another cause for pregnancy loss?

PROBLEM

Previous studies demonstrated that unique tissue-specific antigens expressed on vascular endothelial cells can serve as immunogens, and the apparent association between transplant rejection and antiendothelial cell (EC) antibodies is well established. A common feature of some placentas from women with recurrent pregnancy loss is the diffuse formation of microthrombi associated with changes in thromboresistant properties of endothelial cells, similar to the findings in rejected organs. Therefore, the prevalence of anti-EC antibodies in patients with recurrent pregnancy loss and the role of these antibodies in cultured human endothelial cells from umbilical cord vein were studied.

METHOD OF STUDY

To evaluate the frequency of anti-EC antibodies, sera from 160 nonpregnant patients with recurrent pregnancy loss after absorption with pooled platelets and pooled leukocytes were tested using cultured human umbilical cord vein endothelial cells (HUVEC) by flow cytometry. To study the role of anti-EC antibodies, purified anti-EC IgGs were added to HUVEC cultures and hemostatic, fibrinolytic, and anticoagulation pathway markers (tissue factor, tissue plasminogen activator, palsminogen-activator inhibitor, thrombomodulin, heparan-sulfate proteoglican, antithrombin III, von Willebrand factor, CD54, human leukocyte antigens-DR, and transferin receptor) were detected by specific antibodies and flow cytometry. Immunoblotting analyses were done by using purified anti-EC IgGs against cell membrane proteins from endothelial cells and leukocytes extracted by detergent solubilization.

RESULTS

Thirty-nine (24%) of the patients were positive for EC antibodies. Antipaternal lymphocyte antibodies were tested as well and were found in 37 (23%) of the patients as 25 sera (15.6%) showed reactivity with both EC and lymphocytes. Certain patient sera were reactive with HUVEC lines from some but not other umbilical cords, which suggests allotypy. Sera from 70 normal healthy male and nonpregnant female controls did not react with any of the individual HUVEC lines used. The purified anti-EC immunoglobulin G (IgGs) recognized bands, from HUVEC surface membrane protein preparations, with molecular weights of 120 kDa. Both hemostatic and fibrinolytic pathway markers were found activated in the presence of anti-EC IgGs, suggesting an altered endothelial cell surface activation state.

CONCLUSIONS

The results indicate that anti-EC antibody is another marker for a subset of recurrent spontaneous aborters who may have activation of hemostasis and fibrinolysis as a mechanism involved in their losses.

Anti-endothelial cell antibodies: a need for standardization

Twenty years have passed since the original description of the anti-endothelial cell antibodies (AECA). It is widely acknowledged that the presence of circulating autoantibodies against endothelial cells surface antigens, found in a number of patients with connective tissue disease and vasculitis, is one of the driving mechanisms for the observed vascular injury and might be an important factor in initiating the pathogenesis of vascular abnormalities. AECA data regarding the prevalence, technical problems, presence with other autoantibodies, antigen distribution and immune endothelial cell injury associated with these autoantibodies, requires standardization for determining the precise pathophysiologic and immunologic role of anti-endothelial cell antibodies.

Lack of correlation between IgG T-lymphocyte flow cytometric crossmatches with primary renal allograft outcome

The flow cytometric crossmatch (FCXM) has been reported to be more sensitive and capable of detecting very low levels of antibodies than the normally used complement dependent cytotoxicity test. We studied both the two colour IgG T cell FCXM and CDC-XM in 146 renal allograft recipients, 111 primary and 35 regrafts, of which 26% (29/111) of 1st and 20% (7/35) of regrafts had a positive FCXM. There was no overall correlation between the FCXM results and early graft outcome in primary renal allografts. The FCXM did not appear to have any advantage over the CDC-XM in predicting graft outcome in unsensitized first grafts. In the small number of regrafts studied, a positive FCXM was associated with a higher degree of graft failure. FCXM can exhibit false negative results if sera are used solely neat although these prozone phenomena do not influence subsequent graft outcome.