Chronic Antibody Mediated Rejection of Renal Allografts: Pathological, Serological and Immunologic Features in Nonhuman Primates

The pathogenesis of late renal allograft loss is heterogeneous and difficult to diagnose. We have analyzed renal allografts in nonhuman primates to determine the relationship between alloantibodies and the graft pathology of late graft loss. Seventeen Cynomolgus monkeys were chosen from among those on several protocols for renal allotransplantation with mixed chimerism induction so that animals with and without alloantibodies were included. All animals received transient CD154 blockade and short-term cyclosporine treatment until day 28. Serial blood samples were tested for alloantibodies. Protocol biopsies and autopsy kidneys were scored for pathology and C4d deposition. Group 1, defined by complete lack of C4d deposition (24 tissue samples; 8 recipients), had no detectable alloantibodies (33 serum samples; 1-7 samples per recipient) and no evidence of chronic rejection. Three survived greater than 2 years with normal function and histology. Group 2, defined as having C4d deposition in peritubular capillaries, all made alloantibodies (100%), and most grafts later showed chronic allograft glomerulopathy (89%), and/or arteriopathy (89%). All grafts in Group 2 failed (3-27 months). Pathologic lesions of typical of chronic rejection in humans develop in monkeys, correlate with antecedent alloantibodies/C4d deposition and predict chronic rejection rather than durable accommodation.     

The Spectrum of Antibody-Mediated Renal Allograft Injury: Implications for Treatment

Improvements in anti-HLA antibody detection and diagnostic criteria have increased recognition of antibody-mediated rejection (AMR) following renal transplantation. Therapy of acute AMR is directed toward rapidly lowering circulating donor-specific antibody (DSA) activity. Despite reversal of acute renal dysfunction, however, antibody-secreting plasma cells in spleen and bone marrow are not depleted by treatment and circulating DSA commonly remains detectable in peripheral blood. Sequential ultrastructural studies of renal allografts during acute AMR show progression of microvascular endothelial abnormalities from necrosis and apoptosis to glomerular and peritubular capillary basement membrane duplication, termed transplant glomerulopathy (TG), a manifestation of chronic AMR. Additionally, long-term exposure to anti-HLA antibodies (particularly against class II antigens) is associated with shortened allograft survival and TG even in the absence of documented acute AMR. The association of TG with prior acute AMR and with circulating DSA provides evidence that antibody-mediated allograft injury exists as a spectrum of renal injury. Although effective therapy is available for acute AMR, allografts remain at risk for chronic AMR and shortened survival. The optimum approach to treatment for chronic AMR remains to be determined.     

C4D deposition and positive posttransplant crossmatch are not necessarily markers of antibody-mediated rejection in renal allograft recipients

The aim of the study was to search for serologic, immunopathologic, and morphologic evidence of antibody-mediated rejection (AMR) among patients with acute renal allograft dysfunction. The study included 19 patients with episodes of acute rejection (ARE) within the first year after transplantation. All patients had negative crossmatch tests before transplantation. Patients underwent biopsy for histologic and C4d examinations. All patients were monitored for donor-specific HLA alloantibodies during the first posttransplant year. Complement-dependent cytotoxic crossmatches were performed with donor lymphocytes. In eight patients, the crossmatch test results changed to positive during ARE. In all biopsies except one with cortical infarction, we observed C4d staining (group 1). The biopsies of four patients showed histologic changes of AMR, and all of their grafts were lost. In one patient, cellular and vascular rejection (Banff II) were present; in two, Banff I; and in one, borderline lesions. These results were compared with 11 patients with ARE but negative posttransplant crossmatches and negative staining for C4d (group 2). The histologic findings in the biopsies of these patients were cellular interstitial and vascular rejection (Banff I and Banff II). With no features suggestive of AMR. During the first year after transplantation, the creatinine levels of group 1 patients, were significantly higher than group 2 patients. One-year graft survival was 50% in group 1 and 91% in group 2. CONCLUSIONS: C4d and a positive posttransplant crossmatch were not associated with histologic features of AMR in half of the ARE. Nevertheless, C4d deposition and positive posttransplant crossmatches correlated with allograft injury among renal transplant patients.     

The role of C4d immunostaining in the evaluation of the causes of renal allograft dysfunction.

BACKGROUND: Renal biopsy is the gold standard for diagnosis of acute rejection in renal transplant recipients. The Banff (1997) classification was revised in 2003 incorporating morphological criteria and C4d immunostaining for the diagnosis of acute antibody-mediated rejection. AIMS: The aim of this study was to evaluate the role of histomorphology and C4d immunostaining in indicated renal allograft biopsies with a clinical follow-up for a minimum duration of 1 year. MATERIAL AND METHODS: Histological analysis and C4d immunostaining were performed on 132 needle core biopsies and 2 nephrectomy specimens from 107 patients from July 2004 to June 2005. RESULTS: Histological analysis revealed 59 cases of acute rejection, 10 biopsies of acute tubular necrosis, 41 cases of chronic allograft nephropathy (CAN), either alone or in combination with other diseases, and 18 biopsies of normal morphology. There were four cases of BK nephropathy (BK N) and eight cases had miscellaneous diagnoses. C4d immunostaining was performed on 126 biopsies. Overall, the prevalence of C4d positivity was 45% (57 of 126). Fifty-five percent (28 of 51) of the cases of acute rejection showed C4d positivity including 81% of presumptive antibody-mediated rejection (P-AbAR), 20% acute cellular rejection and 58% acute cellular rejection + P-AbAR. Overall C4d positivity was 37% in chronic allograft nephropathy. Acute tubular necrosis and borderline rejection showed 25 and 50% C4d positivity, respectively. Amongst various histological features, capillary margination of polymorphs and dilatation of peritubular capillaries (PTC-D) showed significant association with C4d positivity (P < 0.005). In cases of CAN, transplant glomerulopathy had significant association with C4d positivity. C4d-positive cases had a higher mean value of serum creatinine at the time of biopsies. CONCLUSION: It is concluded that C4d staining is a useful adjunct marker of the humoral limb of rejection, both in early and late post-transplant periods.     

Current pathological perspectives on chronic rejection in renal allografts

Chronic rejection in renal transplantation clinically manifests as slow deterioration in allograft function and is a major contributor of late renal graft loss. Most cases of chronic rejection involve chronic antibody-mediated rejection (ABMR) triggered by the interaction of donor-specific alloantibodies with endothelial cells of the microcirculation. The evolution of the Banff classification involved a major revision of the ABMR criteria during the 2000s and led to the inclusion of detailed pathological characteristics of chronic ABMR in the 2013 Banff scheme, including microcirculation damage observed as newly formed basement membranes and arterial fibrous intimal proliferation. Inflammation of microvasculature including glomeruli and/or peritubular capillaries is also seen in substantial cases of chronic ABMR, defined as chronic active ABMR. Chronic active T cell-mediated rejection (TCMR) results from chronic T cell-mediated injury involving renal arteries but is less characterized under the current Banff classification, mainly due to the expanding histological criteria of chronic active ABMR. Characteristics shared by these two chronic rejection types can potentially cause diagnostic confusion. Hence, the diagnostic criteria or categories of chronic renal rejection require amendment of the current Banff classification. Assessment of rejection cases with molecular phenotyping advanced the mechanistic understanding of various dysfunctions in renal allograft, including ABMR and TCMR. Identification of disease-specific changes in gene expression by immunohistological studies, especially in chronic ABMR, has already been validated by several studies, warranting potential application to the pathological diagnostic process. This review provides an overview of current pathological perspectives on chronic rejection of renal allografts and future directions.     

Re‐examination of the Lymphocytotoxic Crossmatch in Liver Transplantation: Can C4d Stains Help in Monitoring?

C4d-assisted recognition of antibody-mediated rejection (AMR) in formalin-fixed paraffin-embedded tissues (FFPE) from donor-specific antibody-positive (DSA+) renal allograft recipients prompted study of DSA+ liver allograft recipients as measured by lymphocytotoxic crossmatch (XM) and/or Luminex. XM results did not influence patient or allograft survival, or cellular rejection rates, but XM+ recipients received significantly more prophylactic steroids. Endothelial C4d staining strongly correlates with XM+ (<3 weeks posttransplantation) and DSA+ status and cellular rejection, but not with worse Banff grading or treatment response. Diffuse C4d staining, XM+, DSA+ and ABO- incompatibility status, histopathology and clinical-serologic profile helped establish an isolated AMR diagnosis in 5 of 100 (5%) XM+ and one ABO-incompatible, recipients. C4d staining later after transplantation was associated with rejection and nonrejection-related causes of allograft dysfunction in DSA- and DSA+ recipients, some of whom had good outcomes without additional therapy. Liver allograft FFPE C4d staining: (a) can help classify liver allograft dysfunction; (b) substantiates antibody contribution to rejection; (c) probably represents nonalloantibody insults and/or complete absorption in DSA- recipients and (d) alone, is an imperfect AMR marker needing correlation with routine histopathology, clinical and serologic profiles. Further study in late biopsies and other tissue markers of liver AMR with simultaneous DSA measurements are needed.     

C4d-negative antibody-mediated rejection in renal allografts: evidence for its existence and effect on graft survival

The use of C4d staining as a tissue marker for humoral immunity has served an important role in allowing pathologists to more accurately diagnose acute antibody-mediated rejection (AMR) in renal and other allograft biopsies, and also to recognize the contribution of humoral immunity to lesions of chronic renal allograft rejection, including transplant glomerulopathy. However, while C4d remains a specific marker of a humoral response, recent evidence indicates that a considerable fraction of renal allograft biopsies showing antibody-mediated injury are C4d-negative, even by immunofluorescence. This review summarizes the current evidence supporting the existence of C4d-negative AMR, as well as evidence that this entity may, if untreated, lead to the development of scarring within the graft, transplant glomerulopathy and even graft loss.     

Capillary deposition of complement C4d and C3d in pediatric renal allograft biopsies

BACKGROUND: Peritubular capillary deposition of C4d (C4d(PTC)) is a marker of antibody-mediated alloresponse and is associated with poor graft survival in adults. C3d(PTC) has received less attention; its significance is unclear. To date no information has been gained in children. METHODS: The prevalence of C4d(PTC) and C3d(PTC) in pediatric renal allograft biopsies (n=77, 31 cadaveric kidneys) was analyzed retrospectively. Associations with histology, donor-specific antibodies (DSAs), and outcome were investigated. RESULTS: The overall prevalence of C4d(PTC) and C3d(PTC) was 52% and 48%, respectively. C3d(PTC) was associated with C4d(PTC) (P<0.0001). Thirty-six percent of acute rejections were cellular, 28% were humoral, and 36% were combined cellular and humoral. C3d(PTC) was found in 57% of acute rejection biopsies. C4d(PTC), but not C3d(PTC), was associated with accumulation of polymorphonuclear cells in peritubular capillaries (P=0.02). Fifty-one percent of late biopsies (>6 months posttransplantation) had features of chronic allograft nephropathy: 50% were C4d(PTC_ positive, and 50% were C3d(PTC) positive. C4d(PTC) positive chronic allograft nephropathy biopsies had more transplant glomerulopathy (P=0.020) and mesangial matrix increase (P=0.026). C3d(PTC) tended to be associated with transplant glomerulopathy (P=0.06), but not with mesangial matrix increase. C4d(PTC) was correlated with DSA (P=0.011). Excluding early nonrejection graft losses, more grafts were lost in the C4d(PTC) positive group (P=0.019). C3d(PTC) was not associated with DSA or graft outcome. CONCLUSIONS: Our results support C4d(PTC) being a hallmark of humoral rejection in pediatric renal transplantation; its presence was associated with DSA and poorer immunologic graft outcome. In contrast, C3d(PTC), although highly associated with C4d(PTC), did not correlate with DSA or outcome.     

Therapy with plasmapheresis and intravenous immunoglobulin for acute humoral rejection in kidney transplantation

BACKGROUND: Acute humoral rejection (AHR) is characterized by acute graft dysfunction associated with de novo production of donor-specific alloantibodies (DSA) and C4d deposition in peritubular capillaries of the renal allograft. It has been reported the combination of plasmapheresis (PP) and intravenous gamma globulin (IVIG) as effective rescue therapy for established AHR. METHODS: Between 1999 and 2004, seven kidney allografts recipients suffered from AHR diagnosed by severe rejection and C4d staining in peritubular capillaries. All patients had a negative cross-match before renal transplantation. RESULTS: All patients were treated with daily sessions of PP and in four cases IVIG was added after the last PP session. Tacrolimus and mycophenolate mofetil were employed as maintenance immunosuppressive regimen. In one case, rituximab was added to PP and IVIG owing to refractory humoral rejection. At 1 year, patient survival was 100%, allograft survival was 70%, and the mean serum creatinine was 201 micromol/L. CONCLUSIONS: AHR is a severe form of rejection associated with a poor prognosis, but its early diagnosis and treatment with PP and IVIG allows reversal of AHR reaching a 70% graft survival at 1 year.     

C4d deposition in allografts: current concepts and interpretation

Alloantibody responses are not prevented by the latest immunosuppressive regimens and contribute to increased early and late renal allograft graft loss. Numerous papers have set forth the clinical, pathological, and immunopathological features of acute humoral rejection, in particular the strong correlation between the presence of C4d deposition and circulating antidonor HLA class I and class II antibodies. Humoral rejection also occurs in a chronic setting, associated with chronic allograft glomerulopathy and arteriopathy. C4d deposition can also be found in stable grafts without concurrent graft pathology, a finding that may indicate accommodation. The central diagnostic criterion for humoral rejection is the demonstration of C4d in peritubular capillaries. The criteria for humoral rejection are not as widely accepted for other organs, such as the heart, lung, and pancreas, although humoral rejection, including C4d deposition, has been described. This review focuses on the practical aspects of this test, particularly as applied routinely in renal allografts since 1998 in our laboratory.     

Accompanying renal injuries did not impact graft survival in patients with transplant glomerulopathy

Transplant glomerulopathy (TG) a morphological feature of chronic active antibody-mediated rejection, is associated with donor-specific antibody, peritubular capillary deposition of C4d, and multilayering of peritubular capillary basement membranes. To evaluate the significance of accompanying nonimmunologic injuries in TG, we retrospectively reviewed 2839 renal allograft cases at our institute among which TG was diagnosed in 81 patients (2.9%). Among TG cases, 48 samples showed accompanying diseases such as chronic calcineurin inhibitor toxicity, hepatitis viral infection, posttransplant diabetes, and glomerulonephritis. Comparing the pure form of TG with TG-mixed diseases, there was no difference in patient demography, serum creatinine values, and proteinuria. Among histological parameters, severe hyalinosis was more frequently observed among the TG plus other diseases group. The two groups did not show significant difference in graft survival (P = .216).     

Reducing De Novo Donor-Specific Antibody Levels during Acute Rejection Diminishes Renal Allograft Loss

The effect of de novo DSA detected at the time of acute cellular rejection (ACR) and the response of DSA levels to rejection therapy on renal allograft survival were analyzed. Kidney transplant patients with acute rejection underwent DSA testing at rejection diagnosis with DSA levels quantified using Luminex single-antigen beads. Fifty-two patients experienced acute rejection with 16 (31%) testing positive for de novo DSA. Median follow-up was 27.0 ± 17.4 months postacute rejection. Univariate analysis of factors influencing allograft survival demonstrated significance for African American race, DGF, cytotoxic PRA >20% (current) and/or >50% (peak), de novo DSA, C4d and repeat transplantation. Multivariate analysis showed only de novo DSA (6.6-fold increased allograft loss risk, p = 0.017) to be significant. Four-year allograft survival was higher with ACR (without DSA) (100%) than mixed acute rejection (ACR with DSA/C4d) (65%) or antibody-mediated rejection (35%) (p < 0.001). Patients with >50% reduction in DSA within 14 days experienced higher allograft survival (p = 0.039). De novo DSAs detected at rejection are associated with reduced allograft survival, but prompt DSA reduction was associated with improved allograft survival. DSA should be considered a potential new end point for rejection therapy.     

体液性排斥反应患者移植物组织C4d沉积和浆细胞聚集性浸润初探

目的检测移植肝及肾组织中浆细胞的浸润和补体C4裂解产物C4d的沉积情况,分析浆细胞浸润、C4d沉积与体液性排斥反应的相关性。方法25例肝移植术后出现不同程度肝脏损害的患者的34次经皮肝脏穿刺活体组织病理检查标本与43例因排斥反应而丧失功能的移植肾组织,进行HE染色和免疫组织化学染色,对排斥反应进行病理分型,检测移植物组织中C4d和CD138的表达,分析二者之间的相关性。同时以10例非排斥反应导致移植肾功能丧失者和供肝术前标本作为对照。结果34个移植肝组织标本病理检查诊断为急性排斥反应16个,慢性排斥反应9个,非排斥反应9个。移植前供肝病理标本中均未见C4d沉积,急性排斥反应和慢性排斥反应标本中分别有9／16（56．3％）和5／9（55．6％）见到C4d沉积现象,非排斥反应标本只有1例非吻合口胆管狭窄患者C4d染色也呈阳性（11．1％）。移植肝排斥反应标本中11／25（44．0％）CD138阳性,8／25（32．0％）标本C4d和CD138均阳性。C4d的沉积与CD138的表达存在相关性（r=0．346,P〈0．05）。43例移植肾排斥反应中,超急性排斥反应5例,急性排斥反应9例,慢性排斥反应29例;43例中,C4d阳性19例（44．2％）,CD138阳性24例（55．8％）;有10例（23．3％）C4d和CD138均阳性,C4d的沉积与CD138的表达亦存在相关性（r=0．5051,P〈0．01）。10个对照标本中,C4d阳性1个,无CD138阳性标本。结论CD138与C4d的沉积存在相关性,提示移植肝和肾组织中聚集性浸润的浆细胞可能通过局部分泌抗体的方式参与体液性排斥反应。     

Emerging Concepts and Controversies in Renal Pathology: C4d-Negative and Arterial Lesions as Manifestations of Antibody-Mediated Transplant Rejection

The consensus classification of antibody-mediated rejection (AMR) of renal allografts developed at the Sixth Banff Conference on Allograft Pathology, in 2001, identified three findings necessary for the diagnosis of active AMR: histologic evidence, antibodies against the graft, and capillary C4d deposition. Morphologic and molecular studies have noted evidence of microvascular injury, which, in the presence of donor-specific antibodies (DSAs) but the absence of C4d deposition, is associated with development of transplant glomerulopathy and graft loss. Recent studies suggest that intimal arteritis may in some cases be a manifestation of DSA-induced graft injury. These newly recognized lesions of AMR have now been incorporated into a revised Banff diagnostic schema.     

Capillary deposition of complement split product C4d in renal allografts is associated with basement membrane injury in peritubular and glomerular capillaries: a contribution of humoral immunity to chronic allograft rejection

Endothelial deposition of the complement split product C4d is an established marker of antibody-mediated acute renal allograft rejection. A contribution of alloantibody-dependent immune reactions to chronic rejection is under discussion. In this study, the association of immunohistochemically detected endothelial C4d deposition in peritubular capillaries (PTC) with morphologic features of chronic renal allograft injury was investigated in a large study cohort. C4d deposits in PTC were detected in 73 (34%) of 213 late allograft biopsies performed in 213 patients more than 12 mo after transplantation (median, 4.9 yr) because of chronic allograft dysfunction. Endothelial C4d deposition was found to be associated with chronic transplant glomerulopathy (CG) (P < 0.0001), with basement membrane multilayering in PTC (P = 0.01), and with an accumulation of mononuclear inflammatory cells in PTC (P < 0,001). Furthermore, C4d deposits in PTC (in biopsies with normal glomerular morphology) were associated with development of CG in follow-up biopsies. Other morphologic features of chronic allograft nephropathy (with exception of tubular atrophy) were not associated with C4d deposits in PTC. Analyses of previous and follow-up biopsies revealed that C4d deposits may occur de novo and may also disappear at any time after transplantation. In conclusion, the data suggest that complement activation in renal microvasculature, indicating humoral alloreactivity, contributes to chronic rejection characterized by chronic transplant glomerulopathy and basement membrane multilayering in PTC.     

Early Ultrastructural Changes in Renal Allografts: Correlation With Antibody‐Mediated Rejection and Transplant Glomerulopathy

Transplant glomerulopathy (TG) is associated with antibody‐mediated renal allograft rejection (AMR) and reduced graft survival. Histologically, TG is typically seen >1 year posttransplantation. However, ultrastructural changes including glomerular endothelial swelling, subendothelial widening and early glomerular basement membrane duplication are associated with development of TG but appear much earlier. We examined the specificity of these changes for AMR, and whether these are inevitably associated with development of TG. Of 98 for cause renal allograft biopsies carried out within 3 months of transplantation with available serologic data, 17 showed C4d‐positive AMR and 16 had histologic changes of AMR and donor‐specific antibodies (DSA), but no C4d. All three ultrastructural changes were seen in 11 of 17 biopsies with C4d‐positive AMR, 8 of 16 with histologic changes of AMR and DSA but no C4d, and 0 of 65 without histologic changes of AMR and/or DSA (p < 0.0001 for both of the former groups vs. the latter). Twenty patients with positive DSA (18 with histologic changes of AMR and 11 C4d‐positive) had ≥1 follow‐up biopsy; eight developed overt TG 3.5–30 months posttransplantation. Among the 18 patients with DSA and histologic changes of AMR, 11 C4d‐positive and 7 C4d‐negative, treatment for AMR after the early biopsy significantly reduced subsequent development of overt TG.     

C4d-positive chronic rejection: a frequent entity with a poor outcome

BACKGROUND: Chronic rejection (CR) is an important cause of kidney graft loss. Some studies have suggested the role of antibodies mediating chronic graft dysfunction. In this context, C4d identification is an important tool to evaluate antibody-mediated rejection. METHOD: This is a retrospective study that analyzed 80 patients with histological diagnosis of chronic allograft nephropathy (CAN) according Banff 97 and no evidence of transplant glomerulopathy. These patients had renal biopsies available for C4d immunoperoxidase staining at the time of diagnosis. Cases were reclassified by the presence of C4d in peritubular capillaries. RESULTS: C4d was negative in 30 cases (37.5%) and positive in 50 (62.5%). C4d+ group had more female and highly sensitized patients (PRA) at transplant. All variables were similar between C4d- and C4d+ cases at diagnosis time, but more C4d+ patients presented proteinuria (>0.3 g/L). Patients were submitted to various immunosuppression regimens after the CAN diagnosis. Four years after the diagnosis, death-censored graft survival was 87% for C4d- and 50% for C4d+ (P=0.002). In the multivariate Cox regression analysis, C4d+, PRA>10%, and vascular intimal proliferation were the variables that present higher relative risk for graft loss. CONCLUSION: These data indicate that C4d positive chronic rejection is very common, associated with proteinuria, and has a poor outcome. A larger study is warranted to identify which immunosuppressive regimen may modify the poor course of this entity.     

Association between C4d staining in renal transplant biopsies, production of donor-specific HLA antibodies, and graft outcome

BACKGROUND: We carried out a retrospective study of C4d staining in paraffin sections from renal transplant biopsies to determine the association between C4d staining, donor-specific antibodies (DSA), histological features, and graft outcome. METHODS: We studied 92 patients who had been biopsied for graft dysfunction. Biopsies were classified using Banff 97 criteria and features suggestive of antibody-mediated rejection were noted. Paraffin sections were stained with a polyclonal antibody using an immunoperoxidase technique. The presence of DSA in concurrent sera was determined by enzyme-linked immunosorbent assay and clinical data were reviewed. RESULTS: Of the 92 cases, 15% showed diffuse and 24% showed focal C4d positivity. The grafts failed in 36% of the diffuse (P<0.025), 23% of the focal, and 7% of the negative group at between one month and 15 years posttransplantation. Only patients in the group with diffuse C4d positivity had concurrent DSA (five cases, P<0.001). Of the five DSA-positive patients, three had type II acute rejection and two of these transplants subsequently failed. The remaining two had chronic allograft nephropathy with features of alloimmune injury. Only two of the nine DSA-negative/C4d-positive transplants had failed at the time of writing, in one case due to recurrent disease. CONCLUSION: We demonstrated a significant association between diffuse C4d staining, production of DSA, and graft failure. Although the concurrent detection of DSA and C4d positivity is uncommon in our patients, these results indicate that outcome in this group is poor and they may benefit from therapies directed at the humoral response.     

Antibody-mediated rejection

The introduction of both complement 4d (C4d) staining in renal allograft biopsies and sensitive methods to detect anti-human leukocyte antigen antibodies, such as single antigen bead flow assays, into tissue-typing techniques have shown the importance of antibody-mediated alloimmune response in kidney transplantation. The use of these sensitive methods, combined with the increased number of transplants in highly sensitized patients with donor-specific antibodies, or patients receiving desensitization protocols, have increased the awareness and thus the incidence of acute antibody-mediated rejection. Chronic rejection also can be mediated through alloantibodies, and the term chronic antibody-mediated rejection recently was proposed. In this review article we summarize the current knowledge of the role of alloantibodies in transplantation, the diagnosis and treatment of acute and chronic antibody-mediated rejection, and their effect on graft function and outcome.     

Sinusoidal C4d deposits in liver allografts indicate an antibody-mediated response: diagnostic considerations in the evaluation of liver allografts

There is a paucity of data concerning the correlation of complement component 4d (C4d) staining in liver allografts and antibody-mediated rejection. Data about the location and character of C4d deposits in native and allograft liver tissues are inconsistent. We performed C4d immunofluorescence (IF) on 141 fresh-frozen liver allograft biopsy samples and native livers, documented the pattern of C4d IF staining, and correlated the findings with the presence of donor-specific alloantibodies (DSAs). A linear/granular sinusoidal pattern of C4d IF was noted in 18 of 28 biopsy samples obtained after transplantation from patients with positive crossmatch and detectable donor-specific alloantibody (pos-XM/DSA) findings. None of the 59 tested biopsy samples from patients with negative crossmatch and detectable donor-specific alloantibody (neg-XM/DSA) findings were C4d-positive (P < 0.001). No significant association was found between pos-XM/DSA and C4d IF staining in other nonsinusoidal liver compartments. To compare the results of sinusoidal C4d staining with IF and 2 immunohistochemistry (IHC) techniques, C4d IHC was performed on 19 liver allograft biopsy samples in which a sinusoidal pattern of C4d IF had been noted. Sinusoidal C4d IHC findings were negative for 17 of the 19 biopsy samples; 2 showed weak and focal staining, and both patients had pos-XM/DSA findings. Portal vein endothelium staining was present in only 1 IF-stained biopsy sample (pos-XM/DSA) but in 11 IHC-stained biopsy samples (2 of the 11 samples had neg-XM/DSA findings). We conclude that sinusoidal C4d deposits detected by IF in frozen tissue samples from liver allograft recipients correlate with the presence of DSAs and an antibody-mediated alloresponse. These observations are similar to findings reported for other solid organ transplants and can provide relevant information for patient management. Further validation of IHC techniques for C4d detection in liver allograft tissue is required.