Endothelial Cell Antibodies Associated with Novel Targets and Increased Rejection

Abstract

The initial contact point between a recipient's immune system and a transplanted graft is the vascular endothelium. Clinical studies suggest a pathogenic role for non-HLA antiendothelial cell antibodies (AECAs) in allograft rejection; however, evidence linking AECAs of known specificity to in vivo vascular injury is lacking. Here, we used high-density protein arrays to identify target antigens for AECAs isolated from the sera of recipients of kidney transplants experiencing antibody-mediated rejection in the absence of donor-specific HLA antibodies. Four antigenic targets expressed on endothelial cells were identified: endoglin, Fms-like tyrosine kinase-3 ligand, EGF-like repeats and discoidin I-like domains 3, and intercellular adhesion molecule 4; the first three have been implicated in endothelial cell activation and leukocyte extravasation. To validate these findings, ELISAs were constructed, and sera from an additional 150 renal recipients were tested. All four AECAs were detected in 24% of pretransplant sera, and they were associated with post-transplant donorspecific HLA antibodies, antibody-mediated rejection, and early transplant glomerulopathy. AECA stimulation of endothelial cell cultures increased adhesion molecule expression and production of inflammatory cytokines: regulated on activation, normal T cell expressed and secreted PDGF and RESISTIN. These correlations between in vitro experiments and in vivo histopathology suggest that AECAs activate the vascular endothelium, amplifying the alloimmune response and increasing microvascular damage. Given the growing number of transplant candidates, a better understanding of the antigenic targets, beyond HLA, and mechanisms of immune injury will be essential for improving long-term allograft survival.

Antibody-mediated rejection: New approaches in prevention and management

“…There are efforts under way to use molecular techniques to identify the targets for these antibodies. 105 However, little is currently known about the nature of the majority of non-HLA antibodies, and this topic deserves a separate discussion as the field emerges.…”

Histopathological findings in transplanted kidneys

“…Moreover, Jackson et al discovered four new non-HLA antibodies: endoglin, Fmslike tyrosine kinase-3 ligand, EGF-like repeats and discoidin I-like domains 3, and intercellular adhesion molecule 4. All four AECAs were detected in 24% of pre-transplant sera, and they were associated with post-transplant DSA, ABMR, and early TG [71].…”

Renal Allograft Rejection

“…The robust result in this article is that the anti-ECAs are associated with microvascular pathology and anti-HLA DSA, but an unresolved issue is whether the anti-ECAs are necessarily causing pathologic changes, or are a result of injury due to anti-HLA antibody in those cases in which DSA is demonstrable. 7 As highlighted in other studies, 10 non-HLA antibodies are frequently present in HLA sensitized patients and this association still remains a major potential confounder. Further translational research is needed to define the specific contribution of HLA and non-HLA antibodies in the setting of antibody-mediated endothelial injury.…”

“…Jackson et al 7 address another important issue related to rejection and clinicopathologic correlation: patients with evidence of AMR without demonstrable DSAs. Identification of DSA(s) remains a necessary feature for diagnosis of AMR, 8 and DSA titers are monitored to assess response to treatment in these patients.…”

“…The strategies described in this study, combining in vitro and in vivo studies and serologic and histopathologic evaluation are a model for further investigation in this important area. 7 ELISA-based antibody detection could enable routine testing for non-HLA anti-ECA, optimizing management of both presensitized and nonsensitized graft recipients.…”