Weak Expression of Terminal Complement in Active Antibody-Mediated Rejection of the Kidney

Abstract

BackgroundThe role of the complement system in antibody-mediated rejection (ABMR) is insufficiently understood. We aimed to investigate the role of local and systemic complement activation in active (aABMR). We quantified complement activation markers, C3, C3d, and C5b-9 in plasma of aABMR, and acute T-cell mediated rejection (aTCMR), and non-rejection kidney transplant recipients. Intra-renal complement markers were analyzed as C4d, C3d, C5b-9, and CD59 deposition. We examined in vitro complement activation and CD59 expression on renal endothelial cells upon incubation with human leukocyte antigen antibodies.MethodsWe included 50 kidney transplant recipients, who we histopathologically classified as aABMR (n=17), aTCMR (n=18), and non-rejection patients (n=15).ResultsComplement activation in plasma did not differ across groups. C3d and C4d deposition were discriminative for aABMR diagnosis. Particularly, C3d deposition was stronger in glomerular (P<0,01), and peritubular capillaries (P<0,05) comparing aABMR to aTCMR rejection and non-rejection biopsies. In contrast to C3d, C5b-9 was only mildly expressed across all groups. For C5b-9, no significant difference between aABMR and non-rejection biopsies regarding peritubular and glomerular C5b-9 deposition was evident. We replicated these findings in vitro using renal endothelial cells and found complement pathway activation with C4d and C3d, but without terminal C5b-9 deposition. Complement regulator CD59 was variably present in biopsies and constitutively expressed on renal endothelial cells in vitro.ConclusionOur results indicate that terminal complement might only play a minor role in late aABMR, possibly indicating the need to re-evaluate the applicability of terminal complement inhibitors as treatment for aABMR.

Complement component C3 and C5b‐9 deposition on hypoxia reperfused endothelial cells by non‐HLA antibodies against RhoGDI2: A player involved in graft failure?

“…Treating ECs with PL‐C—and thus removing the natural complement defense—creates a rather artificial situation. However, literature indicate reduced expression of the membrane bound complement regulatory proteins CD46, CD55 and CD59 on rejected renal grafts 34,35 . Literature showed that reduced CD55 expression and increased sensitivity to complement deposition differ per cell type.…”

“…However, literature indicate reduced expression of the membrane bound complement regulatory proteins CD46, CD55 and CD59 on rejected renal grafts. 34 , 35 Literature showed that reduced CD55 expression and increased sensitivity to complement deposition differ per cell type. Downregulation of CD55 did not significantly alter C3 deposition on HUVEC and human NT2‐N neurons, 36 , 37 while loss of CD55 on glomeruli in kidney biopsies and on murine vascular endothelial cells coincides with increased C3 deposition.…”

Histologic and molecular features of antibody-mediated rejection

“…Studies have specifically looked at peritubular capillaries as major targets of AMR and as sites of complement fixation. Tiller et al [6] found in graft biopsies that C3d and C4d deposition discriminated AMR from TCMR, particularly, C3d in glomeruli and peritubular capillaries. C5b-9 was minimally expressed and did not distinguish the groups.…”

Determination of the clinical relevance of donor epitope‐specific HLA‐antibodies in kidney transplantation

“…10,11 In addition, it has been suggested that especially complement binding DSAs are pathogenic. Although biopsies of rejected grafts showed positive C4d deposition, [12][13][14] convincing evidence has emerged that antibody-mediated rejection could also occur in absence of positive C4d staining. 15,16 Although studies showed that the specificity of pre-transplant DSAs (Class I and/or Class II) did not clearly impact long-term transplant outcome, 17 there is also research showing that in particular persistent Class II DSAs are associated with inferior graft survival.…”