Mechanisms of complement activation, C4d deposition, and their contribution to the pathogenesis of antibody-mediated rejection

Complement Membrane Attack Complexes Disrupt Proteostasis to Function as Intracellular Alarmins

Internalized pools of membrane attack complexes (MACs) promote NF-kB and dysregulated tissue inflammation. Here, we show that C9, a MAC-associated protein, promotes loss of proteostasis to become intrinsically immunogenic. Surface-bound C9 is internalized into Rab5 + endosomes whose intraluminal acidification promotes C9 aggregates. A region within the MACPF/CDC domain of C9 stimulates aggrephagy to induce NF-kB, inflammatory genes, and EC activation. This process requires ZFYVE21, a Rab5 effector, which links LC3A/B on aggresome membranes to RNF34-P62 complexes to mediate C9 aggrephagy. C9 aggregates form in human tissues, C9-associated signaling responses occur in three mouse models, and ZFYVE21 stabilizes RNF34 to promote C9 aggrephagy in vivo. Gene-deficient mice lacking ZFYVE21 in ECs showed reduced MAC-induced tissue injury in a skin model of chronic rejection. While classically defined as cytotoxic effectors, MACs may impair proteostasis, forming aggregates that behave as intracellular alarmins.

Genetic determinants of complement activation in the general population

Complement is a fundamental innate immune response component. Its alterations are associated with severe systemic diseases. To illuminate the complement's genetic underpinnings, we conduct genome-wide association studies of the functional activity of the classical (CP), lectin (LP), and alternative (AP) complement pathways in the Cooperative Health Research in South Tyrol study (n = 4,990). We identify seven loci, encompassing 13 independent, pathway-specific variants located in or near complement genes (CFHR4, C7, C2, MBL2) and non-complement genes (PDE3A, TNXB, ABO), explaining up to 74% of complement pathways' genetic heritability and implicating long-range haplotypes associated with LP at MBL2. Two-sample Mendelian randomization analyses, supported by transcriptome- and proteome-wide colocalization, confirm known causal pathways, establish within-complement feedback loops, and implicate causality of ABO on LP and of CFHR2 and C7 on AP. LP causally influences collectin-11 and KAAG1 levels and the risk of mouth ulcers. These results build a comprehensive resource to investigate the role of complement in human health.

Significance of C4d expression in peritubular capillaries concurrent with microvascular inflammation in for-cause biopsies of ABO-incompatible renal allografts

BACKGROUND

Pathologic diagnosis of antibody-mediated rejection (ABMR) in ABO-incompatible (ABOi) transplantation patients is often challenging because patients without ABMR are frequently immunopositive for C4d. The aim of this study was to determine whether C4d positivity with microvascular inflammation (MVI), in the absence of any detectable donor-specific antibodies (DSAs) in ABOi patients, could be considered as ABMR.

METHODS

A retrospective study of 214 for-cause biopsies from 126 ABOi kidney transplantation patients was performed. Patients with MVI score of ≥2 and glomerulitis score of ≥1 (n = 62) were divided into three groups: the absolute ABMR group (DSA-positive, C4d-positive or C4d-negative; n = 36), the C4d-positive group (DSA-negative, C4d-positive; n = 22), and the C4d-negative group (DSA-negative, C4d-negative; n = 4). The Banff scores, estimated glomerular filtration rates (eGFRs), and graft failure rates were compared among groups.

RESULTS

C4d-positive biopsies showed higher glomerulitis, peritubular capillaritis, and MVI scores compared with C4d-negative specimens. The C4d-positive group did not show significant differences in eGFRs and graft survival compared with the absolute ABMR group.

CONCLUSION

The results indicate that C4d positivity, MVI score of ≥2, and glomerulitis score of ≥1 in ABOi allograft biopsies may be categorized and treated as ABMR cases.

Immune-mediated cholangiopathies in children: the need to better understand the pathophysiology for finding the future possible treatment targets

Cholangiopathies are defined as focal or extensive damage of the bile ducts. According to the pathogenetic mechanism, it may be immune-mediated or due to genetic, infectious, toxic, vascular, and obstructive causes. Their chronic evolution is characterized by inflammation, obstruction of bile flow, cholangiocyte proliferation, and progression toward fibrosis and cirrhosis. Immune-mediated cholangiopathies comprise primary sclerosing cholangitis (PSC), autoimmune cholangitis and IgG4-associated cholangitis in adults and biliary atresia (BA), neonatal sclerosing cholangitis (NSC) in children. The main purpose of this narrative review was to highlight the similarities and differences among immune-mediated cholangiopathies, especially those frequent in children in which cholangiocyte senescence plays a key role (BA, NSC, and PSC). These three entities have many similarities in terms of clinical and histopathological manifestations, and the distinction between them can be hard to achieve. In BA, bile duct destruction occurs due to aggression of the biliary cells due to viral infections or toxins during the intrauterine period or immediately after birth. The consequence is the activation of the immune system leading to severe inflammation and fibrosis of the extrahepatic biliary tract, lumen stenosis, and impairment of the biliary flow. PSC is characterized by inflammation and fibrosis of intra- and extrahepatic bile ducts, leading to secondary biliary cirrhosis. It is a multifactorial disease that occurs because of genetic predisposition [human leukocyte antigen (HLA) and non-HLA haplotypes], autoimmunity (cellular immune response, autoantibodies, association with inflammatory bowel disease), environmental factors (infections or toxic bile), and host factors (intestinal microbiota). NSC seems to be a distinct subgroup of childhood PSC that appears due to the interaction between genetic predisposition (HLA B8 and DR3) and the disruption of the immune system, validated by elevated IgG levels or specific antibodies [antinuclear antibody (ANA), anti-smooth muscle antibody (ASMA)]. Currently, the exact mechanism of immune cholangiopathy is not fully understood, and further data are required to identify individuals at high risk of developing these conditions. A better understanding of the immune mechanisms and pathophysiology of BA, NSC, and PSC will open new perspectives for future treatments and better methods of preventing severe evolution.

Cellular activation pathways and interaction networks in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is an evolving field of reconstructive surgery that has revolutionized the treatment of patients with devastating injuries, including those with limb losses or facial disfigurement. The transplanted units are typically comprised of different tissue types, including skin, mucosa, blood and lymphatic vasculature, muscle, and bone. It is widely accepted that the antigenicity of some VCA components, such as skin, is particularly potent in eliciting a strong recipient rejection response following transplantation. The fine line between tolerance and rejection of the graft is orchestrated by different cell types, including both donor and recipient-derived lymphocytes, macrophages, and other immune and donor-derived tissue cells (e.g., endothelium). Here, we delineate the role of different cell and tissue types during VCA rejection. Rejection of VCA grafts and the necessity of life-long multidrug immunosuppression remains one of the major challenges in this field. This review sheds light on recent developments in decoding the cellular signature of graft rejection in VCA and how these may, ultimately, influence the clinical management of VCA patients by way of novel therapies that target specific cellular processes.

HLA antibody affinity determination: From HLA-specific monoclonal antibodies to donor HLA specific antibodies (DSA) in patient serum

Organs transplanted across donor-specific HLA antibodies (DSA) are associated with a variety of clinical outcomes, including a high risk of acute kidney graft rejection. Unfortunately, the currently available assays to determine DSA characteristics are insufficient to clearly discriminate between potentially harmless and harmful DSA. To further explore the hazard potential of DSA, their concentration and binding strength to their natural target, using soluble HLA, may be informative. There are currently a number of biophysical technologies available that allow the assessment of antibody binding strength. However, these methods require prior knowledge of antibody concentrations. Our objective within this study was to develop a novel approach that combines the determination of DSA-affinity as well as DSA-concentration for patient sample evaluation within one assay. We initially tested the reproducibility of previously reported affinities of human HLA-specific monoclonal antibodies and assessed the technology-specific precision of the obtained results on multiple platforms, including surface plasmon resonance (SPR), bio-layer interferometry (BLI), Luminex (single antigen beads; SAB), and flow-induced dispersion analysis (FIDA). While the first three (solid-phase) technologies revealed comparable high binding-strengths, suggesting measurement of avidity, the latter (in-solution) approach revealed slightly lower binding-strengths, presumably indicating measurement of affinity. We believe that our newly developed in-solution FIDA-assay is particularly suitable to provide useful clinical information by not just measuring DSA-affinities in patient serum samples but simultaneously delivering a particular DSA-concentration. Here, we investigated DSA from 20 pre-transplant patients, all of whom showed negative CDC-crossmatch results with donor cells and SAB signals ranging between 571 and 14899 mean fluorescence intensity (MFI). DSA-concentrations were found in the range between 11.2 and 1223 nM (median 81.1 nM), and their measured affinities fall between 0.055 and 24.7 nM (median 5.34 nM; 449-fold difference). In 13 of 20 sera (65%), DSA accounted for more than 0.1% of total serum antibodies, and 4/20 sera (20%) revealed a proportion of DSA even higher than 1%. To conclude, this study strengthens the presumption that pre-transplant patient DSA consists of various concentrations and different net affinities. Validation of these results in a larger patient cohort with clinical outcomes will be essential in a further step to assess the clinical relevance of DSA-concentration and DSA-affinity.

Potential causal role of synovial complement system activation in the development of post-traumatic osteoarthritis after anterior cruciate ligament injury or meniscus tear

Anterior cruciate ligament (ACL) injury and meniscal tear (MT) are major causal factors for developing post-traumatic osteoarthritis (PTOA), but the biological mechanism(s) are uncertain. After these structural damages, the synovium could be affected by complement activation that normally occurs in response to tissue injury. We explored the presence of complement proteins, activation products, and immune cells, in discarded surgical synovial tissue (DSST) collected during arthroscopic ACL reconstructive surgery, MT-related meniscectomy and from patients with OA. Multiplexed immunohistochemistry (MIHC) was used to determine the presence of complement proteins, receptors and immune cells from ACL, MT, OA synovial tissue vs. uninjured controls. Examination of synovium from uninjured control tissues did not reveal the presence of complement or immune cells. However, DSST from patients undergoing ACL and MT repair demonstrated increases in both features. In ACL DSST, a significantly higher percentage of C4d+, CFH+, CFHR4+ and C5b-9+ synovial cells were present compared with MT DSST, but no major differences were seen between ACL and OA DSST. Increased cells expressing C3aR1 and C5aR1, and a significant increase in mast cells and macrophages, were found in ACL as compared to MT synovium. Conversely, the percentage of monocytes was increased in the MT synovium. Our data demonstrate that complement is activated in the synovium and is associated with immune cell infiltration, with a more pronounced effect following ACL as compared to MT injury. Complement activation, associated with an increase in mast cells and macrophages after ACL injury and/or MT, may contribute to the development of PTOA.

HLA class II antibody activation of endothelial cells induces M2 macrophage differentiation in peripheral blood

BACKGROUND

Donor-specific human leukocyte antigen (HLA) class II antibodies (HLA-II Abs) combined with allogeneic endothelial cells (ECs) mediate high-risk rejection in kidney transplant patients. Macrophage accumulation is a significant histological feature of antibody-mediated rejection (AMR) in kidney transplant patients. Here, we further investigated the effect of HLA-II Abs on macrophage phenotypes to provide theoretical basis for clinical treatment of AMR.

METHODS

We prepared an experimental model containing HLA-II Ab-stimulated microvascular ECs and peripheral blood mononuclear cells (PBMCs) co-culture and explored the potential relationship of HLA-II Ab, ECs activation, and macrophage differentiation. Immune phenotype of macrophage subsets was analyzed and quantified by flow cytometry. HLA-II Ab activation of ECs induces M2 macrophage differentiation signal pathways which were investigated by qPCR and western blotting.

RESULTS

The stimulation of ECs by F(ab')₂ fragment of HLA-II Abs led to phosphorylation of PI3K, Akt, and mTOR, which mediated IL-10, ICAM-1, VCAM-1 secretion. The enhanced ICAM-1 and IL-10 promoted the migration of PBMCs and their differentiation into CD68⁺ and CD163⁺ (M2-type) macrophages, respectively, but not CD86⁺ macrophages.

CONCLUSION

These findings revealed the PI3K/Akt/mTOR signal pathways activated by HLA-II Abs in ECs and the immune regulation ability of HLA-II Abs to induce PBMC differentiation.

Association of Circulating Anti-HLA Donor-Specific Antibodies and Their Characteristics, including C1q-Binding Capacity, in Kidney Transplant Recipients with Long-Term Renal Graft Outcomes

Post-transplant antihuman leukocyte antigen donor-specific antibodies (anti-HLA DSAs) monitoring in kidney transplant recipients remains unclear and is currently under investigation. The pathogenicity of anti-HLA DSAs is determined by antibody classes, specificity, mean fluorescent intensity (MFI), C1q-binding capacity, and IgG subclasses. The aim of this study was to investigate the association of circulating DSAs and their characteristics with renal allograft long-term outcomes. The study included 108 consecutive patients from our transplant center who underwent kidney allograft biopsy between November 2018 and November 2020, 3 to 24 months after kidney transplantation. At the time of biopsy, patients' sera were collected for analysis of anti-HLA DSAs. Patients were followed for a median time of 39.0 months (Q1-Q3, 29.8-45.0). Detection of anti-HLA DSAs at the time of biopsy (HR = 5.133, 95% CI 2.150-12.253, p = 0.0002) and their C1q-binding capacity (HR = 14.639, 95% CI 5.320-40.283, p ≤ 0.0001) were independent predictors of the composite of sustained 30% reduction from estimated glomerular filtration rate or death-censored graft failure. Identification of anti-HLA DSAs and their C1q-binding capacity could be useful in identifying kidney transplant recipients at risk for inferior renal allograft function and graft failure. Analysis of C1q is noninvasive, accessible, and should be considered in clinical practice in post-transplant monitoring.

Successful pharmacological intervention at different levels of the complement system in an in vitro complement fixation model for bullous pemphigoid

Bullous pemphigoid (BP) is characterized by deposition of immunoglobulins and complement along the epidermal basement membrane (BM). In humans, there is a lack of functional studies targeting the complement system (CS). This study investigates activation of all complement pathways in BP skin biopsies. Moreover, pharmacological inhibition at different levels of the CS was investigated using anti-complement compounds in a complement fixation BP assay. In this retrospective study, 21 frozen biopsies from BP patients were stained by direct immunofluorescence for C1q, MBL, ficolin-2, C4d, properdin, C3c and C5b-9. Sera from 10 patients were analysed in a complement fixation assay in the presence of C1 inhibitor, anti-factor B monoclonal antibody (mAb), anti-C3 mAb and anti-C5 mAb and compared with dexamethasone. The two readouts were the quantity of complement deposited along the BM and the release of sC5b-9 in the supernatant. Our results show classical and alternative complement pathway activation in BP skin biopsies, but could not demonstrate significant lectin pathway activation. In contrast to dexamethasone, complement deposition along the BM could be selectively inhibited by anti-C1 and anti- factor B. More downstream, selective intervention at the level of C3 and C5 could effectively reduce complement deposition along the BM and the release of sC5b-9 in the supernatant. This study shows that selective intervention in either the classical, alternative or terminal pathway prevented deposition of complement along the BM in an in vitro BP model. The results of our study greatly encourage the clinical development of complement inhibitors for the treatment of BP.

Novel prognostic implications of complement activation in the tumour microenvironment for de novo metastatic BRAF V600E mutant colorectal cancer

BACKGROUND

Prognosis of metastatic BRAF V600E mutant colorectal cancer (CRC) is poor, and the prognostic implications of immune contextures in the tumour microenvironment (TME) for CRC remain elusive.

METHODS

We collected the primary tumour specimens and clinicopathological characteristics of patients with de novo metastatic microsatellite-stable BRAF V600E mutant CRC from two medical centres. Gene expression analysis was performed using the nCounterⓇ PanCancer Immune Profiling Panel. The Cox proportional hazards regression model was used for analysing survival outcomes in association with immune gene expression and immune cells. Our complement score was defined on the basis of the average gene expression in the selected co-expression module.

RESULTS

High expression of classical and regulatory complement genes was significantly associated with poor prognosis (N = 54). A high complement score (defined as a score above the median value) indicated significantly shorter survival. The overall survival (OS) impact of the high score remained significant in multivariate analyses. Additionally, our complement score was strongly correlated with C4d expression in immunohistochemical staining and tumour-associated macrophage (TAM) M2 signatures.

CONCLUSIONS

Complement activation in the TME was significantly associated with poor OS and was correlated with TAM M2 in patients with de novo metastatic BRAF V600E mutant CRC.

In Vivo Kidney Allograft Endothelial Specific Scavengers for On-Site Inflammation Reduction under Antibody-Mediated Rejection

Kidney transplantation is the most effective therapy for patients with end-stage renal disease. However, antibody-mediated rejection (ABMR) threatens long-term survival of renal grafts. Although ABMR can be controlled by donor-specific antibody clearance and B- or (and) plasma-cells inhibition, the treatment often causes severe side effects in patients. Therefore, there is need to explore site-specific scavengers. In this study, a nanovehicle carrying an anti-inflammatory drug is developed with complement component 4d targeting, a specific biomarker expressed on allograft endothelium under ABMR. Moreover, the nanovehicle is endowed with photothermal properties to control drug release. Analysis through systematic in vitro and in vivo toxicity, non-invasive targeted imaging, and in situ remote controlled drug release show the nanovehicle specifically targets allograft kidney endothelium, releases an anti-inflammatory drug, methylprednisolone, locally upon laser irradiation, and promotes recovery of injured endothelium, without affecting systemic inflammation or innate immune responses. This strategy has the potential for future clinical application in ABMR treatment.

The Role of Fc Gamma Receptors in Antibody-Mediated Rejection of Kidney Transplants

For the past decades, complement activation and complement-mediated destruction of allograft cells were considered to play a central role in anti-HLA antibody-mediated rejection (AMR) of kidney transplants. However, also complement-independent mechanisms are relevant in the downstream immune activation induced by donor-specific antibodies, such as Fc-gamma receptor (FcγR)-mediated direct cellular activation. This article reviews the literature regarding FcγR involvement in AMR, and the potential contribution of FcγR gene polymorphisms to the risk for antibody mediated rejection of kidney transplants. There is large heterogeneity between the studies, both in the definition of the clinical phenotypes and in the technical aspects. The study populations were generally quite small, except for two larger study cohorts, which obviates drawing firm conclusions regarding the associations between AMR and specific FcγR polymorphisms. Although FcγR are central in the pathophysiology of AMR, it remains difficult to identify genetic risk factors for AMR in the recipient’s genome, independent of clinical risk factors, independent of the donor-recipient genetic mismatch, and in the presence of powerful immunosuppressive agents. There is a need for larger, multi-center studies with standardised methods and endpoints to identify potentially relevant FcγR gene polymorphisms that represent an increased risk for AMR after kidney transplantation.

TLR7 Activation Accelerates Cardiovascular Pathology in a Mouse Model of Lupus

We report a novel model of lupus-associated cardiovascular pathology accelerated by the TLR7 agonist R848 in lupus-prone B6.Sle1.Sle2.Sle3 (TC) mice. R848-treated TC mice but not non-autoimmune C57BL/6 (B6) controls developed microvascular inflammation and myocytolysis with intracellular vacuolization. This histopathology was similar to antibody-mediated rejection after heart transplant, although it did not involve complement. The TC or B6 recipients of serum or splenocytes from R848-treated TC mice developed a reactive cardiomyocyte hypertrophy, which also presents spontaneously in old TC mice as well as in TC.Rag-/- mice that lack B and T cells. Each of these cardiovascular lesions correspond to abnormalities that have been reported in lupus patients. Lymphoid and non-lymphoid immune cells as well as soluble factors contribute to lupus-associated cardiovascular lesions in TC mice, which can now be dissected using this model with and without R848 treatment.

Contemporary review of heart transplant immunology and immunosuppressive therapy

Background

Survival after heart transplantation (HT) has improved considerably since the first HT was performed in 1967 in Cape Town, South Africa. Understanding immunology behind organ rejection has paved way for advances in the assessment of pre-transplant compatibility, development of newer and more specific immunosuppressive drugs, and management of rejection.

Objectives

Unlike medical therapy for heart failure, transplant protocols vary considerably between different centers. These variations in protocols generally reflect unique population characteristics and the availability of resources. This review article aims to provide a consolidated update on contemporary cardiac transplant medicine. We also aim to highlight local practice and its difference from our international counterparts.

Methods

A literature search was performed on Pubmed and Cochrane Central Register of Controlled Trials to identify trials and review articles that discussed heart transplant immunology and protocols. The International Society for Heart and Lung Transplant (ISHLT) guidelines were also reviewed. We focused on risk factors, prevention strategies, and treatment of cardiac rejection.

Results

A total of 48 articles were selected to provide a comprehensive overview of the contemporary practice of cardiac transplant immunosuppressive therapy. Comparisons were made with local data and practice protocols to highlight key differences.

Conclusion

Heart transplant covers a small subset of cardiac patients and much of the evidence is derived from empirical observations and retrospective analysis. This accounts for the heterogeneity in care and treatment protocols. More studies are needed to select best practices from around the world to further improve outcomes.

Neuropathic symptoms with SARS-CoV-2 vaccination

Background and Objectives

Various peripheral neuropathies, particularly those with sensory and autonomic dysfunction may occur during or shortly after acute COVID-19 illnesses. These appear most likely to reflect immune dysregulation. If similar manifestations can occur with the vaccination remains unknown.

Results

In an observational study, we studied 23 patients (92% female; median age 40years) reporting new neuropathic symptoms beginning within 1 month after SARS-CoV-2 vaccination. 100% reported sensory symptoms comprising severe face and/or limb paresthesias, and 61% had orthostasis, heat intolerance and palpitations. Autonomic testing in 12 identified seven with reduced distal sweat production and six with positional orthostatic tachycardia syndrome. Among 16 with lower-leg skin biopsies, 31% had diagnostic/subthreshold epidermal neurite densities (≤5%), 13% were borderline (5.01-10%) and 19% showed abnormal axonal swelling. Biopsies from randomly selected five patients that were evaluated for immune complexes showed deposition of complement C4d in endothelial cells. Electrodiagnostic test results were normal in 94% (16/17). Together, 52% (12/23) of patients had objective evidence of small-fiber peripheral neuropathy. 58% patients (7/12) treated with oral corticosteroids had complete or near-complete improvement after two weeks as compared to 9% (1/11) of patients who did not receive immunotherapy having full recovery at 12 weeks. At 5-9 months post-symptom onset, 3 non-recovering patients received intravenous immunoglobulin with symptom resolution within two weeks.

Conclusions

This observational study suggests that a variety of neuropathic symptoms may manifest after SARS-CoV-2 vaccinations and in some patients might be an immune-mediated process.

Chronic Inflammatory Placental Disorders Associated With Recurrent Adverse Pregnancy Outcome

Chronic inflammatory placental disorders are a group of rare but devastating gestational syndromes associated with adverse pregnancy outcome. This review focuses on three related conditions: villitis of unknown etiology (VUE), chronic histiocytic intervillositis (CHI) and massive perivillous fibrin deposition (MPFD). The hallmark of these disorders is infiltration of the placental architecture by maternal immune cells and disruption of the intervillous space, where gas exchange between the mother and fetus occurs. Currently, they can only be detected through histopathological examination of the placenta after a pregnancy has ended. All three are associated with a significant risk of recurrence in subsequent pregnancies. Villitis of unknown etiology is characterised by a destructive infiltrate of maternal CD8+ T lymphocytes invading into the chorionic villi, combined with activation of fetal villous macrophages. The diagnosis can only be made when an infectious aetiology has been excluded. VUE becomes more common as pregnancy progresses and is frequently seen with normal pregnancy outcome. However, severe early-onset villitis is usually associated with fetal growth restriction and recurrent pregnancy loss. Chronic histiocytic intervillositis is characterised by excessive accumulation of maternal CD68+ histiocytes in the intervillous space. It is associated with a wide spectrum of adverse pregnancy outcomes including high rates of first-trimester miscarriage, severe fetal growth restriction and late intrauterine fetal death. Intervillous histiocytes can also accumulate due to infection, including SARS-CoV-2, although this infection-induced intervillositis does not appear to recur. As with VUE, the diagnosis of CHI requires exclusion of an infectious cause. Women with recurrent CHI and their families are predisposed to autoimmune diseases, suggesting CHI may have an alloimmune pathology. This observation has driven attempts to prevent CHI with a wide range of maternal immunosuppression. Massive perivillous fibrin deposition is diagnosed when >25% of the intervillous space is occupied by fibrin, and is associated with fetal growth restriction and late intrauterine fetal death. Although not an inflammatory disorder per se, MPFD is frequently seen in association with both VUE and CHI. This review summarises current understanding of the prevalence, diagnostic features, clinical consequences, immune pathology and potential prophylaxis against recurrence in these three chronic inflammatory placental syndromes.

Enrichment of complement, immunoglobulins and autoantibody targets in the proteome of platelets from patients with Systemic Lupus Erythematosus (SLE)

Background  Systemic lupus erythematosus (SLE) is a complex disease characterized by autoimmunity toward apoptotic cells, excessive amounts of circulating immune complexes, and complement activation. A decreased platelet size has been observed in SLE and their nonhemostatic functions may play an active role in the disease. The main objective of this study was to find clues that could explain their decreased size and functional role, analyzing the entire platelet proteome.

Methods  Platelets were isolated from 23 patients with SLE. The five individuals with the highest and lowest average platelet forward scatter were selected for further analysis. Platelet protein content was analyzed using liquid chromatography with tandem mass spectrometry (LC-MS/MS) and compared with platelets from five healthy controls. Data are available via ProteomeXchange with identifier PXD031202.

Results  Out of 2,572 proteins identified, 396 had significantly different levels (ANOVA q -value ≤ 0.01). Forty proteins, including immunoglobulin-, complement- and phosphatidylserine-binding proteins had higher abundance in platelets from SLE patients, largely independent of size (fold difference of ≥1.5 and a t -test p -value of ≤0.05 as cut-off). Functional characterization revealed increased degranulation and skewed hemostatic balance in platelets from SLE patients. In the SLE proteome, immunoglobulin proteins were negatively correlated to serum complement C3 and C4 and the highest relative levels were detected in platelets of normal size.

Conclusion  Platelets from SLE patients shared a specific protein profile, including immunoglobulins, complement proteins, and autoantigens, largely independent of the platelet size and in agreement with an integrated role for platelets in SLE.

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

Background

The 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.

Methods

We included 50 kidney transplant recipients, who we histopathologically classified as aABMR (n=17), aTCMR (n=18), and non-rejection patients (n=15).

Results

Complement 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.

Conclusion

Our 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.

The diagnostic value of immunohistochemical staining of the interstitial vascular C4d complement in membranous nephropathy

Membranous glomerulonephritis (MGN) is the most common cause of adulthood nephrotic syndrome. Diagnosis of membranous nephritis is based on light electron immunofluorescence microscopy and clinical signs. Immune complex deposition against podocyte antigens such as phospholipase A2 receptor (PLA2R) activates the complement system. Of this, complement Component C4d (C4d) is involved in the classical and lectin pathways. This marker may be used by immunohistochemistry to diagnose MGN when other methods are not available. In this work, C4d expression was monitored by immunohistochemical analysis in the glomerular capillaries of patients with primary MGN (study group, N=33) versus patients with minimal change disease (MCD, control group, N=20) in a cross-sectional evaluation performed based on the diagnosis confirmed by light microscopy and immunofluorescence. There was no significant demographic difference between the two groups except for age (P=0.002). C4d immune-expression was positive in glomerular capillary (2+ to 4+) in most of the MGN patients, while it was negative in the MCD group. The sensitivity and specificity of C4d immunostaining were 95% and 100%, respectively. The Pearson correlation coefficient was 0.74 between C4d (immunohistochemistry) and immunoglobulins (IgG; immunofluorescence) and 0.65 between C4d (immunohistochemistry) and the C3 complement product (immunofluorescence). Immunohistochemical evaluation of C4d is, therefore, a sensitive and specific method that has a high correlation with IgG immunofluorescence.

Distinguishing lupus lymphadenitis from Kikuchi disease based on clinicopathological features and C4d immunohistochemistry

OBJECTIVES

Distinguishing Kikuchi disease (KD) from lupus lymphadenitis (LL) histologically is nearly impossible. We applied C4d immunohistochemical (IHC) stain to develop diagnostic tools.

METHODS

We retrospectively investigated clinicopathological features and C4d IHC staining in an LL-enriched development cohort (19 LL and 81 KD specimens), proposed risk stratification criteria and trained machine learning models, and validated them in an external cohort (2 LL and 55 KD specimens).

RESULTS

Clinically, we observed that LL was associated with an older average age (33 vs 25 years; P=0.005), higher proportion of biopsy sites other than the neck [4/19 (21%) vs 1/81 (1%); P=0.004], and higher proportion of generalized lymphadenopathy compared with KD [9/16 (56%) vs 7/31 (23%); P=0.028]. Histologically, LL involved a larger tissue area than KD did (P=0.006). LL specimens exhibited more frequent interfollicular pattern [5/19 (26%) vs 3/81 (4%); P=0.001] and plasma cell infiltrates (P=0.002), and less frequent histiocytic infiltrates in the necrotic area (P=0.030). Xanthomatous infiltrates were noted in 6/19 (32%) LL specimens. Immunohistochemically, C4d endothelial staining in the necrotic area [11/17 (65%) vs 2/62 (3%); P<10-7], and capillaries/venules [5/19 (26%) vs 7/81 (9%); P=0.048] and trabecular/hilar vessels [11/18 (61%) vs 8/81 (10%); P<10-4] in the viable area was more common in LL. During validation, both the risk stratification criteria and machine learning models were superior to conventional histological criteria.

CONCLUSIONS

Integrating clinicopathological and C4d findings could distinguish LL from KD.

Tissue-engineered vascular microphysiological platform to study immune modulation of xenograft rejection

Most of the vascular platforms currently being studied are lab-on-a-chip types that mimic capillary networks and are applied for vascular response analysis in vitro. However, these platforms have a limitation in clearly assessing the physiological phenomena of native blood vessels compared to in vivo evaluation. Here, we developed a simply fabricable tissue-engineered vascular microphysiological platform (TEVMP) with a three-dimensional (3D) vascular structure similar to an artery that can be applied for ex vivo and in vivo evaluation. Furthermore, we applied the TEVMP as ex vivo and in vivo screening systems to evaluate the effect of human CD200 (hCD200) overexpression in porcine endothelial cells (PECs) on vascular xenogeneic immune responses. These screening systems, in contrast to 2D in vitro and cellular xenotransplantation in vivo models, clearly demonstrated that hCD200 overexpression effectively suppressed vascular xenograft rejection. The TEVMP has a high potential as a platform to assess various vascular-related responses.

Chronic histiocytic intervillositis: A breakdown in immune tolerance comparable to allograft rejection?

Chronic histiocytic intervillositis (CHI) is a pregnancy disorder characterized by infiltration of maternal macrophages into the intervillous space of the human placenta, often with accompanying perivillous fibrin deposition. CHI is associated strongly with foetal growth restriction and increased risk of miscarriage and stillbirth. Although rare, affecting 6 in every 10 000 pregnancies beyond 12 weeks' gestation, the rate of recurrence is high at 25%-100%. To date, diagnosis of CHI can only be made post-delivery upon examination of the placenta due to a lack of diagnostic biomarkers, and criteria vary across publications. No treatment options have shown proven efficacy, and CHI remains a serious obstetric conundrum. Although its underlying aetiology is unclear, due to the presence of maternal macrophages and the reported increased incidence in women with autoimmune disease, CHI is hypothesized to be an inappropriate immune response to the semi-allogeneic foetus. Given this lack of understanding, treatment approaches remain experimental with limited rationale. However, there is recent evidence that immunosuppression and antithrombotic therapies may be effective in preventing recurrence of associated adverse pregnancy outcomes. With similarities noted between the pathological features of CHI and acute rejection of solid organ transplants, further investigation of this hypothesis may provide a basis for tackling CHI and other immune-related placental conditions. This review will explore parallels between CHI and allograft rejection and identify areas requiring further confirmation and exploitation of this comparison.

Complement activation on endothelium initiates antibody-mediated acute lung injury

Antibodies targeting human leukocyte antigen (HLA)/major histocompatibility complex (MHC) proteins limit successful transplantation and transfusion, and their presence in blood products can cause lethal transfusion-related acute lung injury (TRALI). It is unclear which cell types are bound by these anti-leukocyte antibodies to initiate an immunologic cascade resulting in lung injury. We therefore conditionally removed MHC class I (MHC I) from likely cellular targets in antibody-mediated lung injury. Only the removal of endothelial MHC I reduced lung injury and mortality, related mechanistically to absent endothelial complement fixation and lung platelet retention. Restoration of endothelial MHC I rendered MHC I-deficient mice susceptible to lung injury. Neutrophil responses, including neutrophil extracellular trap (NET) release, were intact in endothelial MHC I-deficient mice, whereas complement depletion reduced both lung injury and NETs. Human pulmonary endothelial cells showed high HLA class I expression, and posttransfusion complement activation was increased in clinical TRALI. These results indicate that the critical source of antigen for anti-leukocyte antibodies is in fact the endothelium, which reframes our understanding of TRALI as a rapid-onset vasculitis. Inhibition of complement activation may have multiple beneficial effects of reducing endothelial injury, platelet retention, and NET release in conditions where antibodies trigger these pathogenic responses.

Clinical Relevance of Arteriolar C4d Staining in Patients With Chronic-active Antibody-mediated Rejection: A Pilot Study

BACKGROUND

C4d staining in peritubular capillaries is a well-established feature of antibody-mediated rejection (AMR). The relevance of C4d staining outside peritubular capillaries is not well understood. We investigated the significance of arteriolar C4d staining in chronic-active AMR (c-aAMR).

METHODS

All for-cause renal allograft biopsies performed in 2007-2014 at the Erasmus MC and meeting the criteria for suspicious/diagnostic c-aAMR using the Banff Classification 2015 were included. For comparison, renal allograft biopsies from a matched control group and native renal biopsies were analyzed. Arteriolar C4d staining was semiquantitatively scored as negative (0), small deposits in 1 arteriole (1+), small/large deposits in >1 arterioles (2+), or at least extensive deposits in most arterioles (3+).

RESULTS

Thirty-four of 40 (85%) patients with c-aAMR showed arteriolar C4d staining. A significant difference in arteriolar C4d score was observed between cases and matched controls (P = 0.01) and a trend toward significance difference between cases and native renal biopsies (P = 0.05). In the cases, arteriolar C4d staining was significantly associated with severity of arteriolar hyalinosis (P = 0.004) and ≥2 arteriolar C4d staining was independently associated with better graft outcome in a multivariate Cox regression analysis (hazard ratio, 0.260; 95% CI, 0.104-0.650; P = 0.004).

CONCLUSIONS

This pilot study shows that arteriolar C4d staining is more common in biopsies with c-aAMR compared with those without and that it is associated with arteriolar hyalinosis and ≥2 arteriolar C4d staining is associated with superior graft outcome. However, larger studies are needed to examine these findings in more detail to asses if arteriolar C4d staining is truly related to antibody-mediated injury.

Utility of immunohistochemistry with C3d in C3 glomerulopathy

C3-dominance by immunofluorescence is a defining feature in the diagnosis of C3 glomerulopathy. Most pathologists stain for C3c, which has been reported as a trace/negative even in otherwise clear-cut cases of dense deposit disease. We investigated the usefulness of C3d immunohistochemistry in biopsies with C3 glomerulopathy as an ancillary diagnostic tool. All biopsies from patients diagnosed with C3 glomerulopathy in the period January 2005 to June 2017 in the Erasmus MC, Rotterdam were included (n = 14; 10 C3 glomerulonephritis, 4 dense deposit disease). The staining pattern of C3d and C4d by immunohistochemistry was analyzed. As controls, biopsies from patients with immune complex membranoproliferative glomerulonephritis (n = 2), infection-associated glomerulonephritis (n = 6), pauci-immune crescentic glomerulonephritis (n = 7), tubulointerstitial nephritis (n = 7) and chronic-active antibody-mediated rejection (n = 9) were included. All 14 biopsies with C3 glomerulopathy showed a C3d score of ≥2, including two clear-cut biopsies with C3 glomerulopathy originally showing a trace/negative staining for C3c. In the control group, a C3d score ≥2 was observed in 11 biopsies (35%; 2 with immune complex membranoproliferative glomerulonephritis (100%), 6 with infection-associated glomerulonephritis (100%), 1 with pauci-immune crescentic glomerulonephritis (14%), 1 with tubulointerstitial nephritis (14%) and 1 with chronic-active antibody-mediated rejection (11%)). C4d was positive in 71% of the biopsies with C3 glomerulopathy (10/14). In conclusion, C3d immunohistochemistry is a valuable tool in the diagnosis of C3 glomerulopathy, especially in cases in which C3c immunofluorescence shows a trace/negative. We recommend the use of C3d in addition to C3c in cases suspicious for C3 glomerulopathy.

The non-haemostatic role of platelets in systemic lupus erythematosus

Dysregulation of lymphocyte function, accumulation of autoantibodies and defective clearance of circulating immune complexes and apoptotic cells are hallmarks of systemic lupus erythematosus (SLE). Moreover, it is now evident that an intricate interplay between the adaptive and innate immune systems contributes to the pathogenesis of SLE, ultimately resulting in chronic inflammation and organ damage. Platelets circulate in the blood and are chiefly recognized for their role in the prevention of bleeding and promotion of haemostasis; however, accumulating evidence points to a role for platelets in both adaptive and innate immunity. Through a broad repertoire of receptors, platelets respond promptly to immune complexes, complement and damage-associated molecular patterns, and represent a major reservoir of immunomodulatory molecules in the circulation. Furthermore, evidence suggests that platelets are activated in patients with SLE, and that they could contribute to the circulatory autoantigenic load through the release of microparticles and mitochondrial antigens. Herein, we highlight how platelets contribute to the immune response and review evidence implicating platelets in the pathogenesis of SLE.

Epidemiology and Pathophysiology of Glomerular C4d Staining in Native Kidney Biopsies

Introduction

Routine C4d staining in renal transplantation has stimulated its use in kidney biopsies with glomerulonephritis (GN). Methodical description on staining patterns in the native kidney is not available.

Methods

We retrospectively evaluated C4d staining in formalin-fixed paraffin-embedded sections from 519 native kidney biopsies (bx) with and without glomerular disease.

Results

Strong C4d staining was consistently present in immune-complex GN, including lupus nephritis (LN) (n = 68), membranous GN (n = 24), membranoproliferative glomerulonephritis (MPGN) pattern (n = 22), fibrillary GN (n = 3), and proliferative GN with monoclonal IgG (n = 3). C4d stained all cases of postinfectious GN (n = 7) amyloidosis (n = 20) and C1q GN (n = 3). In contrast, IgA nephropathy (IgAN) (n = 34), was negative in 62% of bx, with the rest staining variably. The E1 Oxford classification score correlated with capillary wall C4d staining (P = 0.05). C4d marked the glomerular and arteriolar lesions in thrombotic microangiopathy (TMA; n = 16), the glomerular sclerotic segments in focal segmental glomerulosclerosis (FSGS; n = 77), and marked areas of necrosis in crescentic GN (n = 21). In diabetic glomerulopathy (n = 70), C4d marked advanced insudative lesions but was negative otherwise. C4d weakly stained the mesangium, or was negative in normal biopsies (n = 13), minimal change disease (MCD; n = 21), thin basement membrane disease (n = 20), Alport (n = 3), IgM nephropathy (n = 2), C3 glomerulopathy (n = 5), acute interstitial nephritis (n = 12), acute tubular necrosis (n = 22), ischemic glomerulopathy/nephrosclerosis (n = 23), and other miscellaneous processes (n = 14). Staining in tubular basement membranes and peritubular capillaries was most common in lupus.

Conclusion

Based on reliable staining in lupus and membranous GN, C4d staining is potentially useful as a screening and diagnostic tool, if only paraffin-embedded tissue is available. Knowledge of C4d staining patterns in normal and pathological tissues enhances its diagnostic value.

Intrapulmonary Autoantibodies to HSP72 Are Associated with Improved Outcomes in IPF

Rationale

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic interstitial lung disease, with high mortality. Currently, the aetiology and the pathology of IPF are poorly understood, with both innate and adaptive responses previously being implicated in the disease pathogenesis. Heat shock proteins (Hsp) and antibodies to Hsp in patients with IPF have been suggested as therapeutic targets and prognostic biomarkers, respectively. We aimed to study the relationship between the expression of Hsp72 and anti-Hsp72 antibodies in the BAL fluid and serum Aw disease progression in patients with IPF.

Methods

A novel indirect ELISA to measure anti-Hsp72 IgG was developed and together with commercially available ELISAs used to detect Hsp72 IgG, Hsp72 IgGAM, and Hsp72 antigen, in the serum and BALf of a cohort of IPF (n = 107) and other interstitial lung disease (ILD) patients (n = 66). Immunohistochemistry was used to detect Hsp72 in lung tissue. The cytokine expression from monocyte-derived macrophages was measured by ELISA.

Results

Anti-Hsp72 IgG was detectable in the serum and BALf of IPF (n = 107) and other ILDs (n = 66). Total immunoglobulin concentrations in the BALf showed an excessive adaptive response in IPF compared to other ILDs and healthy controls (p = 0.026). Immunohistochemistry detection of C4d and Hsp72 showed that these antibodies may be targeting high expressing Hsp72 type II alveolar epithelial cells. However, detection of anti-Hsp72 antibodies in the BALf revealed that increasing concentrations were associated with improved patient survival (adjusted HR 0.62, 95% CI 0.45-0.85; p = 0.003). In vitro experiments demonstrate that anti-Hsp72 complexes stimulate macrophages to secrete CXCL8 and CCL18.

Conclusion

Our results indicate that intrapulmonary anti-Hsp72 antibodies are associated with improved outcomes in IPF. These may represent natural autoantibodies, and anti-Hsp72 IgM and IgA may provide a beneficial role in disease pathogenesis, though the mechanism of action for this has yet to be determined.

Successful entecavir plus prednisolone treatment for hepatitis B virus-associated membranoproliferative glomerulonephritis: A case report

RATIONALE

Adult-onset hepatitis B virus-associated membranoproliferative glomerulonephritis (HBV-MPGN) is generally refractory, and an effective treatment for this condition has not been established. The indications for steroids in HBV-MPGN are an important clinical concern.

PATIENT CONCERNS

A 28-year-old woman with a chronic hepatitis B virus infection developed nephrotic syndrome in her second month of pregnancy, with urinary protein levels of 3 to 10 g/d that continued into her postpartum period. She was a carrier of HBV with HBeAg seroconversion. As her renal impairment could have been a result of pregnancy, we observed her for 10 months postpartum without any intervention. However, spontaneous remission after childbirth was not achieved and urine protein levels were sustained at 1 to 3 g/d. About 10 months after delivery, elevated serum liver enzyme levels were observed.

DIAGNOSIS

Biopsies showed MPGN, with deposition of hepatitis B antigen in the glomeruli, and chronic B-type hepatitis with a severity grade of A1F0. She was diagnosed with HBV-MPGN.

INTERVENTIONS

The patient was started on entecavir 0.5 mg/d in March 2008. Within 1 month, serum HBV DNA became undetectable; within 3 months, her alanine aminotransferase levels normalized. However, urinary protein excretion did not decrease to <2 g/d. On a second renal biopsy, performed 7 months after entecavir treatment, proliferative lesions of the glomeruli were observed; therefore, prednisolone was started at an initial dose of 30 mg/d.

OUTCOMES

Her proteinuria improved immediately and prednisolone was tapered over 10 months. A third renal biopsy showed a remarkable resolution of HBV-MPGN, with a significant decrease in mesangial proliferation and immune complex deposition. HBV reactivation was not observed during the prednisolone treatment.

LESSONS

Additional prednisolone therapy in combination with antiviral therapy should be considered for refractory HBV-MPGN, with sufficient care taken regarding HBV reactivation.

Complement factor and T-cell interactions during alloimmune inflammation in transplantation

Complement factor and T-cell signaling during an effective alloimmune response plays a key role in transplant-associated injury, which leads to the progression of chronic rejection (CR). During an alloimmune response, activated complement factors (C3a and C5a) bind to their corresponding receptors (C3aR and C5aR) on a number of lymphocytes, including T-regulatory cells (Tregs), and these cell-molecular interactions have been vital to modulate an effective immune response to/from Th1-effector cell and Treg activities, which result in massive inflammation, microvascular impairments, and fibrotic remodeling. Involvement of the complement-mediated cell signaling during transplantation signifies a crucial role of complement components as a key therapeutic switch to regulate ongoing inflammatory state, and further to avoid the progression of CR of the transplanted organ. This review highlights the role of complement-T cell interactions, and how these interactions shunt the effector immune response during alloimmune inflammation in transplantation, which could be a novel therapeutic tool to protect a transplanted organ and avoid progression of CR.

Sialic acid is a critical fetal defense against maternal complement attack

The negatively charged sugar sialic acid (Sia) occupies the outermost position in the bulk of cell surface glycans. Lack of sialylated glycans due to genetic ablation of the Sia-activating enzyme CMP-sialic acid synthase (CMAS) resulted in embryonic lethality around day 9.5 post coitum (E9.5) in mice. Developmental failure was caused by complement activation on trophoblasts in Cmas-/- implants and was accompanied by infiltration of maternal neutrophils at the fetal-maternal interface, intrauterine growth restriction, impaired placental development, and a thickened Reichert's membrane. This phenotype, which shared features with complement receptor 1-related protein Y (Crry) depletion, was rescued in E8.5 Cmas-/- mice upon injection of cobra venom factor, resulting in exhaustion of the maternal complement component C3. Here we show that Sia is dispensable for early development of the embryo proper but pivotal for fetal-maternal immune homeostasis during pregnancy, i.e., for protecting the allograft implant against attack by the maternal innate immune system. Finally, embryos devoid of cell surface sialylation suffered from malnutrition due to inadequate placentation as a secondary effect.

Development of transplant immunosuppressive agents - considerations in the use of animal models

INTRODUCTION

The development of all immunosuppressant agents to date has involved the experimental use of large and small animal models. Over the last half-century, immunosuppressive drugs have extended the lives of transplant patients worldwide. However, the use of animal models in the development of these drugs is not perfect, and this has brought to light a number of issues including idiosyncratic reactions that are found in animal models but not in humans. The 2006 highly publicized case of the 'elephant man' TGN 1412 drug trial highlights the importance of being cogent of the limitations of animal models. Areas covered: This review covers the utility and limitations of the use of animal models for the development of immunosuppressant agents. This includes both large and small animal models, particularly rodent models in the transplant setting. Expert opinion: The use of animal models represents a critical stage in the development of immunosuppressive drugs. Limitations include physiological differences to humans; this is especially true of immunologically naïve lab rodents with small memory cell populations. Toxic drug levels may differ widely between species. Animal models are also costly and raise ethical concerns. However, there is currently no way to recreate the complex environment of the human immune system purely in vitro.

Molecular Assessment of C4d-Positive Renal Transplant Biopsies Without Evidence of Rejection

Introduction

Immunohistochemical staining for C4d in peritubular capillaries has been part of antibody-mediated rejection (AbMR) definition in the Banff Classification for Allograft Pathology since 2003. However, it has limited sensitivity and specificity, therefore the clinical significance of C4d-positive biopsies without evidence of rejection (C4d+ WER) is unknown. We investigated the transcript levels of genes associated with AbMR in C4d+ WER biopsies from both ABO-compatible and incompatible renal transplant patients.

Methods

RNA was extracted from formalin-fixed paraffin-embedded renal transplant biopsies (n = 125) and gene expression analysis of 35 AbMR-associated transcripts carried out using the NanoString nCounter system.

Results

AbMR-associated transcripts were significantly increased in samples with AbMR or suspicious AbMR. A subgroup of 17 of 35 transcripts that best distinguished AbMR from C4d-negative biopsies without evidence of rejection was used to study C4d+ WER samples. There was no differential expression between C4d-negative and C4d+ WER from both ABO-incompatible and -compatible transplants. The geometric mean of 17 differentially expressed genes was used to assign the C4d+ WER biopsies a high- or low-AbMR transcript score. Follow-up biopsies showed AbMR within 1 year of initial biopsy in 5 of 7 high-AbMR transcript patients but only 2 of 46 low-AbMR transcript patients. In multivariate logistic regression analysis, elevated transcript levels in a C4d+ WER biopsy were associated with increased odds for biopsy-proven AbMR on follow-up (P = 0.032, odds ratio 16.318), whereas factors including donor-specific antibody (DSA) status and time since transplantation were not.

Conclusion

Gene expression analysis in C4d+ WER samples has the potential to identify patients at higher risk of developing AbMR.

Plasma Levels of Complement Factor I and C4b Peptides Are Associated with HIV Suppression

Individuals who exhibit long-term HIV suppression and CD4 T-cell preservation without antiretroviral therapy are of great interest for HIV research. There is currently no robust method for rapid identification of these “HIV controller” subjects; however, HLA-B*57 (human leukocyte antigen (major histocompatibility complex), class I, B*57) genotype exhibits modest sensitivity for this phenotype. Complement C3b and C4b can influence HIV infection and replication, but studies have not examined their possible link to HIV controller status. We analyzed HLA-B*57 genotype and complement levels in HIV-positive patients receiving suppressive antiretroviral therapy, untreated HIV controllers, and HIV-negative subjects to identify factors associated with HIV controller status. Our results revealed that the plasma levels of three C4b-derived peptides and complement factor I outperformed all other assayed biomarkers for HIV controller identification, although we could not analyze the predictive value of biomarker combinations with the current sample size. We believe this rapid screening approach may prove useful for improved identification of HIV controllers.

Circulating complement component 4d (C4d) correlates with tumor volume, chemotherapeutic response and survival in patients with malignant pleural mesothelioma

Only limited information is available on the role of complement activation in malignant pleural mesothelioma (MPM). Thus, we investigated the circulating and tissue levels of the complement component 4d (C4d) in MPM. Plasma samples from 55 MPM patients, 21 healthy volunteers (HV) and 14 patients with non-malignant pleural diseases (NMPD) were measured by ELISA for C4d levels. Tissue specimens from 32 patients were analyzed by C4d immunohistochemistry. Tumor volumetry was measured in 20 patients. We found no C4d labeling on tumor cells, but on ectopic lymphoid structures within the tumor stroma. Plasma C4d levels did not significantly differ between MPM, HV or NMPD. Late-stage MPM patients had higher plasma C4d levels compared to early-stage (p = 0.079). High circulating C4d was associated with a higher tumor volume (p = 0.047). Plasma C4d levels following induction chemotherapy were significantly higher in patients with stable/progressive disease compared to those with partial/major response (p = 0.005). Strikingly, patients with low C4d levels at diagnosis had a significantly better overall survival, confirmed in a multivariate cox regression model (hazard ratio 0.263, p = 0.01). Our findings suggest that circulating plasma C4d is a promising new prognostic biomarker in patients with MPM and, moreover, helps to select patients for surgery following induction chemotherapy.

Impact of complement component 3/4/5 single nucleotide polymorphisms on renal transplant recipients with antibody-mediated rejection

Antibody-mediated rejection (ABMR) is an important risk of allograft dysfunction in kidney transplantation. The complement system is considered to be associated with the generation of alloreative antibodies and donor-specific antibodies. However, the association of complement single nucleotide polymorphisms (SNPs) with ABMR still remained unclear. Blood samples of 199 renal transplant recipients containing 68 with ABMR and 131 with stable graft function were collected, and analyzed by next-generation sequencing with an established gene panel. High quality readout was obtained in 18 C3 SNPs, 9 C4 SNPs and 22 C5 SNPs. Concerning C3 gene polymorphisms, after being adjusted with age, sex and immunosuppressive protocols, rs10411506 and rs2230205 were found to be statistically associated with ABMR in dominant model (rs10411506: OR=2.73, 95% CIs: 1.16, 6.68, P=0.028; rs2230205: OR=2.52, 95% CIs: 1.07, 5.92, P=0.034); rs10411506, rs2230205 and rs2230201 were found different in HET model (rs10411506: OR=3.05, 95% CIs: 1.22, 7.64, P=0.017; rs2230205: OR=2.90, 95% CIs: 1.20, 7.00, P=0.018; rs2230201: OR=2.41, 95% CIs: 1.03, 5.64, P=0.042). The linkage analysis showed relatively high linkage disequilibrium among these SNPs. In addition, no significant correlation was found between C4 SNPs, or C5 SNPs, and the development of ABMR. Our study firstly identified the two SNPs (rs10411506 and rs2230205) in C3 gene were statistically correlated with ABMR in kidney transplantation. These findings may have implications for the diagnosis and prevention of ABMR.

Detection of T and B cells specific complement-fixing alloantibodies using flow cytometry: A diagnostic approach for a resource limited laboratory

BACKGROUND AND OBJECTIVES

Various methods have been reported for the detection of antibodies in recipient sera, which can be human leukocyte antigens (HLAs) or non-HLA specific, complement- or noncomplement fixing, as well as donor T (HLA-Class-I) and/or B cell (HLA-Class-I and II) specific. These alloantibodies play a pivotal role in antibody-mediated renal transplantation rejection. Deposition of C4d in peritubular capillaries of a kidney biopsy is a marker of antibody-mediated rejection. The C4d flow-panel reactive antibodies (PRAs) are a screening method for HLA-specific and complement fixing antibodies. However, the method is limited by the lack of donor specificity.

DESIGN AND SETTINGS

Here, we present a new and simple flow cytometric method referred to as C4d-flow cytometry crossmatch (C4d-FCXM) for the detection of donor-specific (T and/or B cell) and C4d-fixing alloantibodies.

RESULTS

The method was applied in a series of clinical cases and judged to be useful. The method may limit unwanted deferral of the donor due to positivity in C4d Flow-PRA and/or FCXM and may be helpful in prediction of antibody mediated rejections. Furthermore, this method can provide information pretransplant in contrast to kidney biopsy and C4d evaluation done posttransplant.

CONCLUSIONS

We postulate that this method incorporates most of the features of all the available modalities (i.e., National Institute of Health-complement dependent lymphocytotoxicity, FCXM, cytotoxic FCXM and C4d-flowPRA) yet cost-effective and best suited for resource-limited laboratory/ies which is a common scenario in developing countries.

Post-transplant Recurrent Bile Salt Export Pump Disease: A Form of Antibody-mediated Graft Dysfunction and Utilization of C4d

Recurrent bile salt export pump (rBSEP) disease has been reported in progressive familial intrahepatic cholestasis type 2 (PFIC2) patients following liver transplantation (LT) and is often refractory to standard anti-cellular rejection immunosuppressants. The mechanism of rBSEP disease is proposed to be a form of type II hypersensitivity reaction with de novo anti-BSEP antibodies blocking the function of allograft BSEP. Utilization of C4d has not been evaluated in rBSEP. We describe a girl with 3 episodes of rBSEP with severe pruritus at 8.9, 10.3, and 11.0 years post-LT, respectively. Patient's serum reacted with normal liver canaliculi by indirect immunofluorescence (IF), whereas patient's liver showed canalicular immunoglobulin G deposition. The histologic features of all 3 liver biopsies recapitulate PFIC2 with cholestatic giant cell hepatitis. Canalicular BSEP expression was not detected in areas of feathery degeneration by immunohistochemistry, but was retained in morphologically normal liver. By direct IF, C4d showed diffuse sinusoidal staining in the third biopsy. Patient responded well to rituximab with or without intravenous immunoglobulin with subsiding symptoms and normalization of serum bile acid levels. In conclusion, rBSEP disease should be considered in the differential diagnosis when evaluating for rejection in a PFIC2 patient post-LT presenting with pruritus. A portion of liver core may be snap frozen in OCT medium for possible direct IF for C4d, that can serve as a surrogate marker for complement activation and antibody-mediated graft dysfunction.

Classical complement pathway activation in the nasal tissue of patients with chronic rhinosinusitis

BACKGROUND

Complement plays a major role in inflammatory diseases, but its involvement and mechanisms of activation in patients with chronic rhinosinusitis (CRS) are not known.

OBJECTIVES

After earlier studies discovering autoantibodies in patients with CRS, we sought to investigate the nature, extent, and location of complement activation in nasal tissue of patients with CRS. Specifically, we were interested in whether antibody-mediated activation through the classical pathway was a major mechanism for complement activation in patients with CRS.

METHODS

Nasal tissue was obtained from patients with CRS and control subjects. Tissue homogenates were analyzed for complement activation products (ELISA-C5b-9, C4d, activated C1, and C5a) and major complement-fixing antibodies (Luminex). Tissue sections were stained for C5b-9, C4d, and laminin. Antibodies were purified with protein A/G columns from nasal polyps (NP), matching patient serum, and control serum and assayed for basement membrane binding by means of ELISA.

RESULTS

C5b-9 levels were significantly increased in NP tissue compared with uncinate tissue (UT) of patients with chronic rhinosinusitis with nasal polyps (CRSwNP) and those with chronic rhinosinusitis without nasal polyps (CRSsNP; P < .01). Similarly, C4d levels were increased in NPs compared with UT of patients with CRSwNP, patients with CRSsNP, and control subjects (P < .05). Activated C1 levels were also increased in NP tissue compared with UT of patients with CRSsNP and control subjects (P < .05) and correlated with levels of C5a (P < .01), local immunoglobulins (especially IgM, P < .0001), and anti-double-stranded DNA IgG (P < .05). Immunofluorescence showed that C5b-9 and C4d deposition occurred linearly along the epithelial basement membrane. NP tissue extracts had significantly more anti-basement membrane antibodies than sera from patients with CRSwNP and control subjects (P < .0001).

CONCLUSION

Levels of C5b-9, C4d, and activated C1 were significantly increased locally in NP tissue. C5b-9 and C4d were almost universally deposited linearly along the basement membrane of NP tissue. Furthermore, activated C1 levels were best correlated with local immunoglobulin and C5a levels. Together, these data suggest that the classical pathway plays a major role in complement activation in patients with CRS.

Donor-specific anti-HLA antibodies with antibody-mediated rejection and long-term outcomes following heart transplantation

BACKGROUND

Donor-specific anti-HLA antibodies (DSA) are common after heart transplantation and are associated with rejection, cardiac allograft vasculopathy, and mortality. A noninvasive diagnostic test for pathologic antibody-mediated rejection (pAMR) does not exist.

METHODS

From January 1, 2010, through August 31, 2013, 221 consecutive adult patients underwent heart transplantation and were followed through October 1, 2015. The primary objective was to determine whether the presence of DSA could detect AMR at the time of pathologic diagnosis. Secondary analyses included association of DSA (stratified by major histocompatibility complex class and de novo status) during AMR with new graft dysfunction, graft loss (mortality or retransplantation), and development of cardiac allograft vasculopathy.

RESULTS

During the study period, 69 patients (31.2%) had DSA (24% had de novo DSA), and there were 74 episodes of pAMR in 38 patients. Sensitivity of DSA at any mean fluorescence intensity to detect concurrent pAMR was only 54.3%. The presence of any DSA during pAMR increased the odds of graft dysfunction (odds ratio = 5.37; 95% confidence interval [CI], 1.34-21.47; p = 0.018), adjusting for age, sex, and timing of AMR. Circulating class II DSA after transplantation increased risk of future pAMR (hazard ratio = 2.97; 95% CI, 1.31-6.73; p = 0.009). Patients who developed de novo class II DSA had 151% increased risk of graft loss (contingent on 30-day survival) compared with patients who did not have DSA (95% CI, 1.11-5.69; p = 0.027).

CONCLUSIONS

DSA were inadequate to diagnose pAMR. Class II DSA provided prognostic information regarding future pAMR, graft dysfunction with pAMR, and graft loss.

Unraveling the Role of Allo-Antibodies and Transplant Injury

Alloimmunity driving rejection in the context of solid organ transplantation can be grossly divided into mechanisms predominantly driven by either T cell-mediated rejection (TCMR) and antibody-mediated rejection (ABMR), though the co-existence of both types of rejections can be seen in a variable number of sampled grafts. Acute TCMR can generally be well controlled by the establishment of effective immunosuppression (1, 2). Acute ABMR is a low frequency finding in the current era of blood group and HLA donor/recipient matching and the avoidance of engraftment in the context of high-titer, preformed donor-specific antibodies. However, chronic ABMR remains a major complication resulting in the untimely loss of transplanted organs (3-10). The close relationship between donor-specific antibodies and ABMR has been revealed by the highly sensitive detection of human leukocyte antigen (HLA) antibodies (7, 11-15). Injury to transplanted organs by activation of humoral immune reaction in the context of HLA identical transplants and the absence of donor specific antibodies (17-24), strongly suggest the participation of non-HLA (nHLA) antibodies in ABMR (25). In this review, we discuss the genesis of ABMR in the context of HLA and nHLA antibodies and summarize strategies for ABMR management.

Desensitization strategies in adult heart transplantation-Will persistence pay off?

Strategies are needed to enable successful heart transplantation in highly sensitized patients. Immunologic challenges from sensitization to human leukocyte antigen (HLA) reduce access to compatible donors, extend waiting times to transplant, and increase the risks of antibody-mediated rejection and cardiac allograft vasculopathy after transplant. The prime goal of desensitization is to increase access to transplantation through expansion of the donor organ pool. Existing therapies are directed at key components of the humoral immune response with newer biologically based regimens able to target plasma cells as the source of antibody production, as well as complement activation that has a central role in antibody-mediated injury. Despite the emergence of early promising results for these agents, a significant knowledge gap remains with the current data for desensitization, extrapolated mostly from non-heart solid-organ transplants and small observational studies. Notably, no approach has demonstrated significant and sustainable reductions in HLA antibody pre-transplant, and the ideal desensitization strategy remains elusive. In addition, clinical tools to evaluate the humoral response and efficacy of therapy are limited, focusing almost exclusively on HLA antibody detection. Importantly, desensitization is associated with significant costs and potential risks, and overall long-term outcomes and cost-effectiveness have not been sufficiently evaluated. Investigation is ongoing into the development of a clinically effective desensitization strategy in heart transplantation.

Antibody-mediated rejection of the lung: A consensus report of the International Society for Heart and Lung Transplantation

Antibody-mediated rejection (AMR) is a recognized cause of allograft dysfunction in lung transplant recipients. Unlike AMR in other solid-organ transplant recipients, there are no standardized diagnostic criteria or an agreed-upon definition. Hence, a working group was created by the International Society for Heart and Lung Transplantation with the aim of determining criteria for pulmonary AMR and establishing a definition. Diagnostic criteria and a working consensus definition were established. Key diagnostic criteria include the presence of antibodies directed toward donor human leukocyte antigens and characteristic lung histology with or without evidence of complement 4d within the graft. Exclusion of other causes of allograft dysfunction increases confidence in the diagnosis but is not essential. Pulmonary AMR may be clinical (allograft dysfunction which can be asymptomatic) or sub-clinical (normal allograft function). This consensus definition will have clinical, therapeutic and research implications.

Tolerogenic Dendritic Cells on Transplantation: Immunotherapy Based on Second Signal Blockage

Dendritic cells (DCs), the most important professional antigen-presenting cells (APC), play crucial role in both immunity and tolerance. It is well known that DCs are able to mount immune responses against foreign antigens and simultaneously tolerate self-antigens. Since DCs can be modulated depending on the surrounding microenvironment, they can act as a bridge between innate and adaptive immunity. However, the mechanisms that support this dual role are not entirely clear. Recent studies have shown that DCs can be manipulated ex vivo in order to trigger their tolerogenic profile, what can be a tool to be used in clinical trials aiming the treatment of various diseases and the prevention of transplant rejection. In this sense, the blockage of costimulatory molecules on DC, in the attempt of inhibiting the second signal in the immunological synapse, can be considered as one of the main strategies under development. This review brings an update on current therapies using tolerogenic dendritic cells modulated with costimulatory blockers with the aim of reducing transplant rejection. However, although there are current clinical trials using tolerogenic DC to treat allograft rejection, the actual challenge is to modulate these cells in order to maintain a permanent tolerogenic profile.

Early decreased plasma levels of factor B and C5a are important biomarkers in children with Kawasaki disease

BACKGROUND

The mechanisms underpinning Kawasaki disease (KD) are incompletely understood. There is an unmet need for specific biomarkers for the early diagnosis of KD.

METHODS

Eighty-five KD patients suffering from acute-phase and subacute-phase KD, 40 healthy children, and 40 febrile children comprised the study cohort. An enzyme-linked immunosorbent assay was used to measure plasma levels of C1q, C1q-circulating immune complex (C1q-CIC), mannan-binding lectin-associated serine protease (MASP)-1, factor B, C4d, C3d, C5a, C5b-9 and CD59.

RESULTS

Plasma concentrations of factor B and C5a in the acute phase were lower than those in healthy and febrile control groups (all P < 0.05). Compared with acute-phase KD patients, plasma concentrations of C1q, factor B, and C3d in KD patients were increased significantly (P < 0.05), but those of C4d, MASP-1 and CD59 decreased significantly (P < 0.05), in patients with sub-acute KD.

CONCLUSION

These data suggest that more than one pathway in the complement system is activated in KD. Importantly, decreased plasma concentrations of factor B and C5a in the acute phase (6-10 d) could be employed as biomarkers for the early diagnosis of KD.

An Anti-C1s Monoclonal, TNT003, Inhibits Complement Activation Induced by Antibodies Against HLA

Antibody-mediated rejection (AMR) of solid organ transplants (SOT) is characterized by damage triggered by donor-specific antibodies (DSA) binding donor Class I and II HLA (HLA-I and HLA-II) expressed on endothelial cells. While F(ab')2 portions of DSA cause cellular activation and proliferation, Fc regions activate the classical complement cascade, resulting in complement deposition and leukocyte recruitment, both hallmark features of AMR. We characterized the ability of an anti-C1s monoclonal antibody, TNT003, to inhibit HLA antibody (HLA-Ab)-induced complement activation. Complement deposition induced by HLA-Ab was evaluated using novel cell- and bead-based assays. Human aortic endothelial cells (HAEC) were cultured with HLA-Ab and human complement; production of activated complement proteins was measured by flow cytometry. Additionally, C3d deposition was measured on single antigen beads (SAB) mixed with HLA-Ab and human complement. TNT003 inhibited HLA-Ab mediated complement deposition on HAEC in a concentration-dependent manner; C3a, C4a and C5a anaphylatoxin production was also diminished by TNT003. Finally, TNT003 blocked C3d deposition induced by Class I (HLAI-Ab)- and Class II (HLAII-Ab)-specific antibodies on SAB. These data suggest TNT003 may be useful for modulating the effects of DSA, as TNT003 inhibits complement deposition and split product formation generated by HLA-I/II-Ab in vitro.