Table of Contents
Definition / general | Essential features | Terminology | ICD coding | Epidemiology | Sites | Pathophysiology | Etiology | Diagrams / tables | Clinical features | Diagnosis | Laboratory | Radiology description | Radiology images | Case reports | Treatment | Clinical images | Gross description | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Immunofluorescence description | Immunofluorescence images | Positive stains | Negative stains | Electron microscopy description | Electron microscopy images | Molecular / cytogenetics description | Molecular / cytogenetics images | Sample pathology report | Differential diagnosis | Additional references | Practice question #1 | Practice answer #1 | Practice question #2 | Practice answer #2Cite this page: Reyes F, Arkun K, Basu A. Antibody mediated rejection. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/heartantibodymediatedrejection.html. Accessed April 29th, 2025.
Definition / general
- Antibody mediated rejection (AMR) is a form of allograft rejection characterized by the presence of donor specific antibodies (DSA) directed against human leukocyte antigens (HLA) on the donor endothelium (Circulation 2015;131:1608)
- Diagnosis of AMR involves histological evidence of endothelial damage, immunopathologic findings such as C4d deposition and the presence of circulating DSA (Circulation 2015;131:1608)
Essential features
- Endomyocardial biopsy remains a critical diagnostic tool for AMR (Circulation 2015;131:1608)
- Histologic features of AMR include activated intravascular mononuclear cells / endothelial cells as well as macrophages (J Heart Lung Transplant 2013;32:1147)
- Intravascular macrophages accumulate in capillaries and venules
- Endothelial cells are prominent with large nucleoli
- Severe AMR shows interstitial edema, myocyte necrosis, mixed inflammatory infiltrate and endothelial pyknosis or karyorrhexis
- Characteristic immunologic features of AMR are capillary deposition of immunoglobulins (IgG, IgM or IgA) and complement activation product (C3d, C4d or C1q) either by immunofluorescence (IF) or by immunohistochemistry (IHC) (J Heart Lung Transplant 2011;30:601)
Terminology
- Antibody mediated allograft rejection (Circulation 2015;131:1608)
ICD coding
Epidemiology
- Incidence of AMR is higher in the first year posttransplant (asymptomatic AMR is diagnosed in 13.6% of biopsies within the first year) (J Heart Lung Transplant 2012;31:46)
- Risk factors include elevated panel reactive antibodies (PRA), cytomegalovirus (CMV) seropositivity, prior mechanical circulatory support and the presence of DSA (J Heart Lung Transplant 2012;31:46)
- F > M (J Heart Lung Transplant 2012;31:46)
Sites
- Myocardium: interstitial capillary injury leading to swollen endothelial cells and intravascular macrophages in myocardial tissue
- Coronary arteries: as part of long term consequence of chronic AMR, cardiac allograft vasculopathy (CAV) involving the distal coronary arteries shows circumferential diffuse concentric narrowing of the arteries especially in the epicardium and myocardium (Front Cardiovasc Med 2022;9:919036, Tex Heart Inst J 2013;40:395)
Pathophysiology
- AMR in heart transplantation is primarily driven by the interaction between recipient antibodies and donor HLA on the endothelial cells of the allograft
- This interaction initiates a cascade of immune responses that leads to graft injury
- Antibody binding and complement activation
- In this phase, recipient antibodies, particularly DSAs, bind to HLA antigens on the endothelial cells of the graft → activation of classical complement pathway → deposition of complement components such as C4d and C3d on the endothelium → endothelial cell activation, which is characterized by endothelial cell swelling, upregulation of adhesion molecules and increased expression of proinflammatory cytokines and chemokines → inflammatory cell recruitment with activated endothelial cells would recruit various immune cells, including macrophages, natural killer (NK) cells and T cells, which infiltrate the graft and contribute to tissue injury through the release of inflammatory mediators and direct cytotoxic effects → at the end, microvascular injury and thrombosis where the inflammatory response leads to increased vascular permeability, interstitial edema and microvascular thrombosis, ultimately resulting in impaired blood flow and ischemic injury to the graft tissue
- Interaction also could be associated with non-HLA antibodies in the absence of detectable anti-HLA antibodies; these are antiendothelial cell antibodies which bind endothelium and result in apoptosis but not in complement mediated lysis; these antibodies appear to be generated by cytomegalovirus infection (Circulation 2015;131:1608)
- 3 types of AMR are reported
- Hyperacute AMR
- Devastating injury on transplanted heart by high levels of preformed DSAs
- Not common due to meticulous crossmatching
- Type 1 AMR
- Early onset AMR due to a memory response in sensitized patients
- Prevented by crossmatching and seen primarily in cases where a weak DSA exists
- Better outcome
- Type 2 AMR
- Later onset due mainly to de novo DSA production
- Most common group
- Worse outcome
- Hyperacute AMR
- References: Circulation 2015;131:1608, Nephron 2020;144:2, Transplantation 2023;107:27
Etiology
- Both immunologic and nonimmunologic elements
- DSAs: preformed DSAs are a significant risk factor for AMR; the intensity of DSAs, measured by mean fluorescence intensity (MFI), also correlates with the risk of AMR (Am J Transplant 2019;19:1160)
- Recipient gender: female recipients have a higher risk of AMR compared to male recipients (Am J Transplant 2019;19:1160)
- Thymic function: enhanced thymic function (indicated by higher levels of recent thymic emigrant CD4+ T cells and T cell receptor excision circles) is associated with an increased risk of AMR (Am J Transplant 2018;18:964)
- Viral infections: early posttransplant infections with human cytomegalovirus and Epstein-Barr virus (EBV) are associated with an increased risk of AMR (Front Immunol 2023;14:1171197)
- Histopathologic and immunopathologic markers: the presence of C4d and CD68 on endomyocardial biopsies, particularly when both are present simultaneously (pAMR2 grade), is predictive of clinical AMR (Transplantation 2015;99:586)
- Non-HLA antibodies: elevated reactivity to non-HLA autoantigens has been associated with AMR, particularly in patients who are also DSA positive (Am J Transplant 2020;20:2571)
Clinical features
- Subclinical
- Complement activation (C4d deposition) without organ dysfunction in cardiac allograft recipients, hence no symptoms (Circulation 2015;131:1608)
- Symptomatic
- Mild heart failure
- Arrhythmias (Am J Cardiol 2001;88:280)
- Palpitations
- Cardiogenic shock
- Syncope
- Fever (rare)
- Presentations of acute cellular rejection (ACR) and AMR are not distinct
- Chronic AMR can lead to chronic cardiac allograft vasculopathy (CAV) which is a long term complication after heart transplantation
Diagnosis
- On endomyocardial biopsy, this is a combined diagnosis based on histology and immunohistochemistry (J Heart Lung Transplant 2013;32:1147)
- Histologic evidence of AMR includes (see Microscopic / histologic description)
- Capillary endothelial swelling or denudation
- Interstitial edema
- Intravascular macrophages
- May have mild pericapillary neutrophilic infiltration, with or without hemorrhage
- Immunologic evidence of AMR includes
- Immunohistochemistry and immunofluorescence have comparable sensitivity and specificity
- Diffuse positivity for C4d or C3d by immunohistochemistry in > 50% of capillary endothelium by immunofluorescence performed on frozen tissue
- Diffuse and strong staining (> 50%) for C4d or C3d by immunohistochemistry method on formalin fixed, paraffin embedded tissues
- CD68 to show intravascular macrophages
- CD68+ cells in > 10% of capillaries with intravascular macrophages is considered immunophenotypic evidence of AMR
- See Diagrams / tables
- AMR grading criteria by the 2011 and 2013 International Society for Heart and Lung Transplantation (ISHLT) consensus guidelines (J Heart Lung Transplant 2011;30:601, J Heart Lung Transplant 2013;32:1147)
- Relies on the presence of histologic / morphologic and immunophenotypic evidence of antibody mediated tissue injury; without the requirements for clinical dysfunction or positive DSAs
- pAMR0: no histologic or immunophenotypic evidence of AMR
- pAMR1(H+): histologic AMR only; histologic evidence of AMR but no immunophenotypic evidence (complement or CD68 are negative)
- pAMR1(I+): immunopathologic AMR only; no histologic evidence of AMR but immunophenotypic evidence is present (CD68+ or C4d+ for immunohistochemistry and C4d+ with or without C3d+ for immunofluorescence)
- pAMR2: both histologic and immunopathologic evidence of AMR are present
- pAMR3: severe pathologic AMR with vasculitis, hemorrhage, edema and diffuse necrosis
- Relies on the presence of histologic / morphologic and immunophenotypic evidence of antibody mediated tissue injury; without the requirements for clinical dysfunction or positive DSAs
- Serologic
- Detection of DSAs against HLA; these antibodies can be identified using techniques such as single antigen bead assays, which allow for the precise detection of HLA specific antibodies in the serum of transplant recipients
- In the absence of detectable anti-HLA antibodies, the assessment of non-HLA antibodies may be indicated where the patient has clinical or pathological evidence of AMR (Circulation 2015;131:1608)
- Molecular
- Molecular Microscope Diagnostic System (MMDx): analyzes RNA transcripts of transplanted heart tissue to differentiate among T cell mediated rejection (TCMR), AMR, injury and healthy tissue
- Screening for rejection, including AMR, is performed at regular intervals after organ transplant (during the first year after transplant [usually 2 weeks], then at 1, 3, 6 and 12 months)
Laboratory
- Elevated serum markers
- High sensitivity troponin (hs-troponin) and B type natriuretic peptide (BNP): not specific for AMR (they indicate myocardial damage and heart insufficiency respectively)
- Donor derived cell free DNA (dd-cfDNA): released from damaged donor heart cells and can be quantified relative to the amount of background circulating recipient cell free DNA
- Increase in the percentage of dd-cfDNA in the blood indicates injury to the transplanted (i.e., donor) heart that may be caused by ACR or AMR, as well as other forms of injury, such as cardiac allograft vasculopathy (Sci Transl Med 2014;6:241ra77)
- Circulating DSAs: DSAs against HLA
- Presence is a critical component for the diagnosis of AMR; these antibodies can be identified using techniques such as single antigen bead assays (SAB), which allow for the precise detection of HLA specific antibodies in the serum of transplant recipients (Circulation 2015;131:1608)
- Few studies mentioned that the sensitivity of DSA is only ~54.3%; however, it could be variable (J Heart Lung Transplant 2017;36:540)
- Luminex SAB has a sensitivity of 88% and a specificity of 68% over lambda LABScreen assay for the diagnosis of AMR (Transplantation 2019;103:597)
Radiology description
- Echocardiogram (Eur Heart J Case Rep 2019;3:ytz100)
- Nonspecific
- Worsening of the left ventricular ejection fraction
- Usually normal left ventricular diameter but increased intraventricular septal thickness and posterior wall thickness
- Magnetic resonance imaging (MRI) (JACC Cardiovasc Imaging 2019;12:1632)
- Notably edema (through T2 mapping) and interstitial expansion or fibrosis
- Pre and postgadolinium contrast T1 mapping to quantify extracellular volume fraction
- Cardiovascular magnetic resonance (CMR) imaging (J Cardiovasc Magn Reson 2018;20:59)
- T2 and T1 mapping is a promising technique for characterizing myocardial tissue
- Applies a combination of noncontrast (T1 and T2 mapping) as well as gadolinium enhance technique
- Evaluates morphology of myocardium, ventricular volumes, systolic dysfunction
- Also assesses inflammatory changes using myocardial edema, hyperemia and injury
Radiology images
Case reports
- 40 year old woman with postpartum cardiomyopathy presented a Wolff-Parkinson-White pattern in the setting of AMR after heart transplant (HeartRhythm Case Rep 2023;9:649)
- 42 year old woman with eosinophilic infiltration as the initial trace of acute mixed cellular AMR and concomitant epitope associated HLA antibody production (Front Immunol 2023;14:1207373)
- 56 year old woman with AMR and development of non-HLA antibodies specific for AT1R in the absence of DSAs (Int J Mol Sci 2024;25:2218)
- 57 year old man with end stage heart failure received a genetically engineered pig heart (Lancet 2023;402:397)
- 67 year old man with hyperacute graft dysfunction in an orthotopic heart transplant in the presence of non-HLA antibodies (Am J Transplant 2020;20:593)
- 74 year old man with severe acute cellular rejection with associated pAMR1 (I+) AMR with ST segment elevation in leads I and aVL (Circ Heart Fail 2015;8:836)
Treatment
- Supportive treatments for cardiac dysfunction, such as cardiogenic shock and arrhythmias
- Initial immunomodulatory therapy: a typical initial treatment regimen depends on the degree of AMR and is individualized; for acute AMR, it consists of combination therapy with intravenous (IV) glucocorticoids and intravenous immunoglobulin (IVIG), antithymocyte globulin, apheresis
- Additional immune therapy: upon completion of initial therapy, practice varies but may include follow up therapy with rituximab, bortezomib or other immunomodulating agents or changes to long term immunosuppression may include the addition of oral glucocorticoids, high dose antimetabolite (e.g., mycophenolate mofetil) or transition to a regimen that contains sirolimus or everolimus
- Reference: Circulation 2015;131:1608
Clinical images
Gross description
- Rare finding at autopsy or retransplant
- Edematous, swollen heart with foci of myocardial discoloration and hemorrhage
Gross images
Microscopic (histologic) description
- Classic histopathologic features of AMR on H&E stained sections include (J Heart Lung Transplant 2013;32:1147)
- Interstitial capillary injury with swollen endothelial cells in myocardium
- Intravascular macrophages in myocardium
- Activated mononuclear cells refer to both the endothelial and macrophage components
- Edema is typically found in association with activated mononuclear cells and rarely is a solitary finding; it is pale eosinophilic to dull basophilic proteinaceous strands between myocytes and around intramyocardial venules and arterioles producing separation of the myocytes, vessels and connective tissue elements
- Severe AMR is characterized by hemorrhage and neutrophilic infiltrates in and around the microvasculature
- Severe AMR also includes intravascular thrombi and myocyte necrosis, as well as karyorrhectic debris in the absence of cellular rejection
- See Diagrams / tables
Microscopic (histologic) images
Contributed by Fabiola Reyes, M.D., Atreyee Basu, M.D. and Knarik Arkun, M.D.
Immunofluorescence description
- Primary panel includes C4d, C3d and anti-HLA-DR
- Optional secondary panel includes fibrin and immunoglobulins
- Immunofluorescence staining on paraffin immunohistochemistry is limited
- Prognostic significance of C3d on frozen specimen is reported
- Intensity ranges from 0 - 3+
- Distributions of staining patterns are divided as < 10%, 10 - 50% and > 50%
- Reporting of the staining for immunofluorescence is described in Table 3
- Reference: J Heart Lung Transplant 2013;32:1147
Immunofluorescence images
Positive stains
- C4d paraffin section, primary panel; only capillary staining counts; granular stain in C4d is possible but should consider negative / nonspecific
- CD68 paraffin section, primary panel
- CD163 paraffin section
- CD34 or CD31: endothelial markers, to assess microvascular integrity
- C3d: not commonly used; however, if done, interpretation criteria would be the same as C4d
- Reference: J Heart Lung Transplant 2013;32:1147
Negative stains
- CD3 (pan-T cell markers) negative in interstitial or perivascular distribution, which is seen in cellular rejection
- Can have both cellular rejection and AMR; should be assessed for both and classified separately (J Heart Lung Transplant 2013;32:1147)
Electron microscopy description
- Minimal ultrastructural evidence of endothelial swelling in low grade rejection
- Intramyocardial capillary with circumferential cytoplasmic and nuclear swelling of the endothelial cells in high grade AMR
- DSA positivity often correlates with degree of endothelial swelling
- Higher degree of endothelial swelling observed in pAMR2 and pAMR1 (H+) compared to pAMR1 (I+) and cellular rejection
- Reference: Am J Transplant 2017;17:496
Molecular / cytogenetics description
- Molecular Microscope Diagnostic System (MMDx) is a novel tool used for the diagnosis of AMR in heart transplant biopsies
- MMDx utilizes microarray technology to measure gene expression profiles in endomyocardial biopsies
- Machine learning algorithms to interpret these profiles and compare them to a large reference set of biopsies allows for the classification of rejection states (Transplantation 2023;107:27)
- Molecularly, 3 types of AMR selective transcripts are reported: NK, interferon gamma (IFNG) inducible and endothelial
- NK cell transcripts such as granulysin (GNLY) and granzyme B (GZMB) are highly associated with AMR
- Reference: Transplantation 2023;107:27
Sample pathology report
- Heart transplant, myocardium, biopsy:
- There is no evidence of acute cellular rejection, 2004 ISHLT 0R (1990 ISHLT grade 0)
- There is no evidence of AMR (pAMR0) (see comment)
- Comment: There are 3 adequate fragments of myocardium for evaluation. Immunohistochemical stains for C4d and CD68 are negative for capillary staining and intravascular macrophages, respectively, supporting the diagnosis.
- Heart transplant, myocardium, biopsy:
- There is no evidence of acute cellular rejection, 2004 ISHLT 0R (1990 ISHLT grade 0)
- There is histologic evidence of AMR, pAMR1 (H+) (see comment)
- Quilty lesion
- Comment: There are 3 adequate fragments of myocardium for evaluation. On histology, prominent endothelial cells and patchy edema are seen in the myocardium (features of histologic AMR). However, immunohistochemical stain for C4d is negative for capillary staining and CD68 immunostain is predominantly negative for intravascular macrophages. The overall findings support the diagnosis and do not appear to meet the immunohistochemical criteria for AMR.
Differential diagnosis
- Acute cellular rejection:
- Peritransplant / operative ischemic injury:
- Inflammatory infiltrate composed of mixed neutrophils, eosinophils, lymphocytes and macrophages
- Coagulative type myocyte necrosis, fat necrosis, contraction band necrosis and myocyte vacuolization frequently extend to the endocardial surface
- Infection (e.g., cytomegalovirus, myocarditis, toxoplasmosis, disseminated aspergillosis):
- Serology positive
- Demonstration of infectious entity on endomyocardial biopsy
Additional references
Practice question #1
A 55 year old woman with a history of dilated cardiomyopathy undergoes orthotopic heart transplantation. 1 month posttransplant, she presents with worsening dyspnea and elevated cardiac enzymes. Endomyocardial biopsy reveals the histology shown above with the diffuse presence of C4d deposition in the capillaries (> 50%). Which of the following is the most likely mechanism underlying her condition?
- Cellular infiltration by T lymphocytes
- Direct cytotoxicity by donor specific antibodies (DSAs)
- Graft versus host disease
- Inflammation mediated by infectious organism
- Quilty lesion
Practice answer #1
B. Direct cytotoxicity by donor specific antibodies (DSAs). The presence of C4d deposition in the capillaries signifies the activation of the complement system due to DSAs. The mechanism of AMR involves DSAs binding to endothelial cell antigens, triggering cytotoxic effects, complement activation and subsequent inflammatory responses, all of which contribute to graft dysfunction. Answer A is incorrect because cellular infiltration by T lymphocytes typically does not activate the complement system. As a result, C4d deposition would be negative in cases of cellular rejection. Answer C is incorrect because graft versus host disease is a rare complication in solid organ transplants, primarily involving a T lymphocyte response. Answer D is incorrect because inflammation caused by infectious organisms typically presents with diffuse lymphocytic eosinophils or histiocytic infiltration of the myocardium and an identifiable microorganism is sometimes present. Answer E is incorrect because Quilty lesion consists of a cellular infiltrate made up of T and B lymphocytes, macrophages and occasional plasma cells, often found on the endocardial surface. The pathogenesis of Quilty lesions is largely unknown; however, it is hypothesized to have an association with cyclosporin based immunosuppressive regimens.
Comment Here
Reference: Antibody mediated rejection
Comment Here
Reference: Antibody mediated rejection
Practice question #2
A 62 year old man underwent a heart transplant due to ischemic heart disease. He is treated with a combination of immunosuppressive medications. 5 weeks after surgery, he developed acute rejection characterized by high fever, malaise and chest discomfort. Laboratory studies showed elevated titers of antidonor antibodies and a biopsy revealed evidence of antibody mediated rejection. Which of the following findings is indicative of antibody mediated rejection?
- C4d deposition in capillaries (multifocal staining)
- Lymphocytic infiltrate in interstitial or perivascular distribution of myocardium
- Mixed inflammation with myocyte necrosis
- Subendocardial lymphocytic aggregate with prominent blood vessels
- Transmural inflammation with eosinophils and myocyte injury
Practice answer #2
A. C4d deposition in capillaries (multifocal staining). C4d deposition in the capillaries serves as a marker for antibody mediated rejection, indicating complement activation triggered by antibodies binding to the vascular endothelium, which leads to tissue injury. Answers B, C and D are incorrect because in a clinical context, the presence of high titers of antidonor antibodies alongside C4d positivity confirms acute antibody mediated rejection, distinguishing it from acute cellular rejection (answer B), peritransplant injury (answer C) and Quilty lesion (answer D). Answer E is incorrect because transmural inflammation with eosinophil and myocyte injury is seen in eosinophilic myocarditis. C4d deposition in the capillaries would not be present in this condition.
Comment Here
Reference: Antibody mediated rejection
Comment Here
Reference: Antibody mediated rejection