Accelerated Clearance and Degradation of Cell-Free HIV by Neutralizing Antibodies Occurs via FcγRIIb on Liver Sinusoidal Endothelial Cells by Endocytosis.

Neutralizing Abs suppress HIV infection by accelerating viral clearance from blood circulation in addition to neutralization. The elimination mechanism is largely unknown. We determined that human liver sinusoidal endothelial cells (LSEC) express FcγRIIb as the lone Fcγ receptor, and using humanized FcγRIIb mouse, we found that Ab-opsonized HIV pseudoviruses were cleared considerably faster from circulation than HIV by LSEC FcγRIIb. Compared with humanized FcγRIIb-expressing mice, HIV clearance was significantly slower in FcγRIIb knockout mice. Interestingly, a pentamix of neutralizing Abs cleared HIV faster compared with hyperimmune anti-HIV Ig (HIVIG), although the HIV Ab/Ag ratio was higher in immune complexes made of HIVIG and HIV than pentamix and HIV. The effector mechanism of LSEC FcγRIIb was identified to be endocytosis. Once endocytosed, both Ab-opsonized HIV pseudoviruses and HIV localized to lysosomes. This suggests that clearance of HIV, endocytosis, and lysosomal trafficking within LSEC occur sequentially and that the clearance rate may influence downstream events. Most importantly, we have identified LSEC FcγRIIb-mediated endocytosis to be the Fc effector mechanism to eliminate cell-free HIV by Abs, which could inform development of HIV vaccine and Ab therapy.

Chronic Active Antibody-Mediated Rejection with Linear IgG Deposition on Glomerular Capillaries in a Kidney Transplant Recipient.

Glomerular IgG deposition is rarely observed in antibody-mediated rejection. Here, we report chronic active antibody-mediated rejection with linear IgG deposition on glomerular capillary walls in a pediatric kidney transplant recipient. A 6-year-old boy with bilateral renal hypoplasia underwent preemptive deceased-donor kidney transplantation. Five years after the transplantation, an allograft biopsy revealed chronic active antibody-mediated rejection with diffuse linear IgG deposition on glomerular capillaries. Anti-glomerular basement membrane antibody, donor-specific anti-human leukocyte antigen (HLA) antibodies, and anti-angiotensin II type 1 receptor antibody were negative. A multiplex antibody assay identified anti-major histocompatibility complex class I chain-related molecule A antibody. Additionally, a single-antigen bead assay identified autoantibodies to 12 non-HLA antigens, including vimentin and glutathione S-transferase theta-1. To investigate whether IgG autoantibodies in the patient's serum bind to antigens on glomerular capillaries, we incubated the patient's serum with 0-h biopsy specimens of tissue donated to the patient and a control subject, both obtained immediately after nephrectomy from respective donors. IgG signals were observed in neither patient nor control samples. Nevertheless, linear IgG deposition may be explained by the binding of autoantibodies to non-HLA antigens that are usually hidden and only exposed via severe endothelial cell injury. Further studies are needed to confirm the significance of non-HLA antibodies in glomerular IgG deposition.

Liver sinusoidal endothelial cell ICAM-1 mediated tumor/endothelial crosstalk drives the development of liver metastasis by initiating inflammatory and angiogenic responses.

The prometastatic stroma generated through tumor cells/host cells interaction is critical for metastatic growth. To elucidate the role of ICAM-1 on the crosstalk between tumor and primary liver sinusoidal endothelial cells (LSECs) and hepatic stellate cells (HSCs), implicated in tumor adhesion and angiogenesis, we performed in vitro cocultures and an in vivo model of liver metastasis of colorectal cancer (CRC). ICAM-1 blockade in the LSECs decreased the adhesion and transmigration of tumor cells through an LSEC in vitro and vivo. Cocultures of C26 cells and LSECs contained higher amounts of IL-1ß, IL-6, PGE-2, TNF-α and ICAM-1 than monocultures. C26 cells incubated with sICAM-1 secreted higher amounts of PGE-2, IL-6, VEGF, and MMPs, while enhanced the migration of LSECs and HSCs. HSCs cultures activated by media from C26 cells pretreated with sICAM-1 contained the largest amounts of VEGF and MMPs. C26 cell activation with sICAM-1 enhanced their metastasizing potential in vivo, while tumor LFA-1 blockade reduced tumor burden and LSECs and HSC-derived myofibroblasts recruitment. In vivo ICAM-1 silencing produced similar results. These findings uncover LSEC ICAM-1 as a mediator of the CRC metastatic cascade in the liver and identifies it as target for the inhibition of liver colonization and metastatic progression.

Critical role for PI3Kγ-dependent neutrophil reactive oxygen species in WKYMVm-induced microvascular hyperpermeability.

PI3K has been indicated in regulating microvascular permeability changes during inflammation. However, its role in neutrophil-driven microvascular leakage in acute inflammation remains unclear. Using intravital microscopy in mice, we examined the role of PI3Kγ and PI3Kδ in formyl peptide WKYMVm- and chemokine CXCL2-induced permeability changes and assessed simultaneously neutrophil adhesion and emigration in post-capillary venules of murine cremaster muscle. We found a PI3Kγ-specific mechanism in WKYMVm-induced but not CXCL2-induced microvascular hyperpermeability. The increased microvascular permeability triggered by WKYMVm was not entirely due to neutrophil adhesion and emigration in cremasteric microvasculature in different PI3K transgenic mouse strains. The PI3Kγ-specific hyperpermeability was neutrophil-mediated as this was reduced after depletion of neutrophils in mouse circulation. Chimeric mice with PI3Kγ-deficient neutrophils but wild-type endothelium also showed reduced hyperpermeability. Furthermore, we found that the catalytic function of PI3Kγ was required for reactive oxygen species (ROS) generation in neutrophils stimulated with WKYMVm. Pharmacological scavenging PI3Kγ-dependent ROS in the tissue eliminated the discrepancy in hyperpermeability between different PI3K transgenic mice and alleviated WKYMVm-induced microvascular leakage in all mouse strains tested. In conclusion, our study uncovers the critical role for PI3Kγ-dependent ROS generation by neutrophils in formyl peptide-induced microvascular hyperpermeability during neutrophil recruitment.

The CD40-ATP-P2X 7 Receptor Pathway: Cell to Cell Cross-Talk to Promote Inflammation and Programmed Cell Death of Endothelial Cells.

Extracellular adenosine 5'-triphosphate (ATP) functions not only as a neurotransmitter but is also released by non-excitable cells and mediates cell-cell communication involving glia. In pathological conditions, extracellular ATP released by astrocytes may act as a "danger" signal that activates microglia and promotes neuroinflammation. This review summarizes in vitro and in vivo studies that identified CD40 as a novel trigger of ATP release and purinergic-induced inflammation. The use of transgenic mice with expression of CD40 restricted to retinal Müller glia and a model of diabetic retinopathy (a disease where the CD40 pathway is activated) established that CD40 induces release of ATP in Müller glia and triggers in microglia/macrophages purinergic receptor-dependent inflammatory responses that drive the development of retinopathy. The CD40-ATP-P2X7 pathway not only amplifies inflammation but also induces death of retinal endothelial cells, an event key to the development of capillary degeneration and retinal ischemia. Taken together, CD40 expressed in non-hematopoietic cells is sufficient to mediate inflammation and tissue pathology as well as cause death of retinal endothelial cells. This process likely contributes to development of degenerate capillaries, a hallmark of diabetic and ischemic retinopathies. Blockade of signaling pathways downstream of CD40 operative in non-hematopoietic cells may offer a novel means of treating diabetic and ischemic retinopathies.

Platelet retention in inflamed glomeruli occurs via selective prolongation of interactions with immune cells.

Platelet-leukocyte interactions promote acute glomerulonephritis. However, neither the nature of the interactions between platelets and immune cells nor the capacity of platelets to promote leukocyte activation has been characterized in this condition. We used confocal intravital microscopy to define the interactions of platelets with neutrophils, monocytes, and endothelial cells in glomerular capillaries in mice. In the absence of inflammation, platelets underwent rapid on/off interactions with immune cells. During glomerulonephritis induced by in situ immune complex formation, platelets that interacted with neutrophils or monocytes, but not with other intraglomerular cells, were retained in the glomerulus for prolonged durations. Depletion of platelets inhibited both neutrophil recruitment and activation. Inhibition of platelet activating factor reduced neutrophil recruitment without impacting reactive oxygen species generation, while blocking CXC chemokine ligand 7 (CXCL7) reduced both responses. In contrast, inhibition of the adenosine diphosphate and thromboxane A2 pathways inhibited neutrophil reactive oxygen species generation without affecting neutrophil adhesion. Thus, platelet retention in glomerular capillaries following immune complex deposition stems from prolongation of platelet interactions with immune cells but not other substrates. Pro-inflammatory mediators play divergent roles in promoting neutrophil retention and activation in glomerular capillaries.

Thrombotic microangiopathy with intraglomerular IgM pseudothrombi in Waldenström macroglobulinemia and IgM monoclonal gammopathy.

IgM secreting myelomas or lymphomas, including Waldenström macroglobulinemia, are associated with a varied spectrum of renal pathology, including intracapillary hyaline deposits, cryoglobulin, membranoproliferative glomerulonephritis, amyloid, monoclonal immunoglobulin deposition disease, cast nephropathy, and lymphoma infiltration. We report our single institution experience, and describe five cases with distinctive glomerular pathology: intracapillary IgM pseudothrombi and thrombotic microangiopathic change, with glomerular intracellular crystals in two biopsies. Two patients were hypocomplementemic at presentation. This series adds to the recent literature on paraprotein associated thrombotic microangiopathy.

Intracapillary immune complexes recruit and activate slan-expressing CD16+ monocytes in human lupus nephritis.

Lupus nephritis is a major cause of morbidity in patients with systemic lupus erythematosus. Among the different types of lupus nephritis, intracapillary immune complex (IC) deposition and accumulation of monocytes are hallmarks of lupus nephritis class III and IV. The relevance of intracapillary ICs in terms of monocyte recruitment and activation, as well as the nature and function of these monocytes are not well understood. For the early focal form of lupus nephritis (class III) we demonstrate a selective accumulation of the proinflammatory population of 6-sulfo LacNAc+ (slan) monocytes (slanMo), which locally expressed TNF-α. Immobilized ICs induced a direct recruitment of slanMo from the microcirculation via interaction with Fc γ receptor IIIA (CD16). Interestingly, intravenous immunoglobulins blocked CD16 and prevented cell recruitment. Engagement of immobilized ICs by slanMo induced the production of neutrophil-attracting chemokine CXCL2 as well as TNF-α, which in a forward feedback loop stimulated endothelial cells to produce the slanMo-recruiting chemokine CX3CL1 (fractalkine). In conclusion, we observed that expression of CD16 equips slanMo with a unique capacity to orchestrate early IC-induced inflammatory responses in glomeruli and identified slanMo as a pathogenic proinflammatory cell type in lupus nephritis.

Antibody-mediated rejection in pediatric small bowel transplantation: Capillaritis is a major determinant of C4d positivity in intestinal transplant biopsies.

The diagnostic criteria for antibody-mediated rejection (ABMR) after small bowel transplantation (SBT) are not clearly defined, although the presence of donor-specific antibodies (DSAs) has been reported to be deleterious for graft survival. We aimed to determine the incidence and prognostic value of DSAs and C4d in pediatric SBT and to identify the histopathologic features associated with C4d positivity. We studied all intestinal biopsies (IBx) obtained in the first year posttransplantation (N = 345) in a prospective cohort of 23 children. DSAs and their capacity to fix C1q were identified by using Luminex technology. Eighteen patients (78%) had DSAs, and 9 had the capacity to fix C1q. Seventy-eight IBx (22.6%) were C4d positive. The independent determinants of C4d positivity were capillaritis grades 2 and 3 (odds ratio [OR] 4.02, P = .047 and OR 5.17, P = .003, respectively), mucosal erosion/ulceration (OR 2.8, P = .019), lamina propria inflammation grades 1 and 2/3 (OR 1.95, P = .043 and OR 3.1, P = .016, respectively), and chorion edema (OR 2.16, P = .028). Complement-fixing DSAs and repeated C4d-positive IBx were associated with poor outcome (P = .021 and P = .001, respectively). Our results support that capillaritis should be considered as a feature of ABMR in SBT and identify C1q-fixing DSAs and repeated C4d positivity as potential markers of poor outcome.

Expression of CD34 and CD146 vascular markers contributes to the immunological function of the human palatine tonsil.

The fundamental function of the palatine tonsil is the immune response to airborne and foodborne pathogenic agents. Small blood vessels have an important role in the provision of a special microenvironment in which the immune response occurs. In this study, we investigated the expression of vascular markers CD34 and CD146 and basal lamina marker - type IV collagen - in the small blood vessels of the human palatine tonsil in the context of their role in the immunological function of the tonsil. The tonsils were collected after tonsillectomy from ten patients with chronic tonsillitis, aged 18-28 years. Five-µm-thick paraffin sections were routinely stained with haematoxylin and eosin, while the studied markers (CD34, CD146 and type IV collagen) were detected immunohistochemically using LSAB2/HRP method. CD34 was expressed equally in the capillaries within and below the crypt epithelium, in lymphoid follicles and in high endothelial venules localized para- and interfollicularly. CD146 molecule was expressed on the luminal surface of endothelial cells in the capillaries of the crypt epithelium, while its expression in high endothelial venules was seen on the luminal and lateral surfaces of the cuboidal endothelial cells. In contrast to the basal lamina of intraepithelial capillaries, where collagen IV-immunopositivity is mostly seen as a continuing line, the basal lamina of high endothelial venules was seen as a two- or three-layered structure beneath the cuboidal endothelial cells. The specifics of expression of CD34, CD146, and type IV collagen confirm the morphofunctional specialization of endothelium in crypt epithelium capillaries, and also in endothelium of high endothelial venules, which is directly associated with the role of these vessels in the immune function of the tonsil.

Liver Sinusoidal Endothelial Cell: An Update.

This update focuses on two main topics. First, recent developments in our understanding of liver sinusoidal endothelial cell (LSEC) function will be reviewed, specifically elimination of blood-borne waste, immunological function of LSECs, interaction of LSECs with liver metastases, LSECs and liver regeneration, and LSECs and hepatic fibrosis. Second, given the current emphasis on rigor and transparency in biomedical research, the update discusses the need for standardization of methods to demonstrate identity and purity of isolated LSECs, pitfalls in methods that might lead to a selection bias in the types of LSECs isolated, and questions about long-term culture of LSECs. Various surface markers used for immunomagnetic selection are reviewed.

Neutrophil FcγRIIA promotes IgG-mediated glomerular neutrophil capture via Abl/Src kinases.

The kidney glomerular capillaries are frequent sites of immune complex deposition and subsequent neutrophil accumulation in post-infectious and rapidly progressive glomerulonephritis. However, the mechanisms of neutrophil recruitment remain enigmatic, and there is no targeted therapeutic to avert this proximal event in glomerular inflammation. The uniquely human activating Fc receptor FcγRIIA promotes glomerular neutrophil accumulation and damage in anti-glomerular basement membrane-induced (anti-GBM-induced) glomerulonephritis when expressed on murine neutrophils. Here, we found that neutrophils are directly captured by immobilized IgG antibodies under physiological flow conditions in vitro through FcγRIIA-dependent, Abl/Src tyrosine kinase-mediated F-actin polymerization. Biophysical measurements showed that the lifetime of FcγRIIA-IgG bonds increased under mechanical force in an F-actin-dependent manner, which could enable the capture of neutrophils under physiological flow. Kidney intravital microscopy revealed that circulating neutrophils, which were similar in diameter to glomerular capillaries, abruptly arrested following anti-GBM antibody deposition via neutrophil FcγRIIA and Abl/Src kinases. Accordingly, inhibition of Abl/Src with bosutinib reduced FcγRIIA-mediated glomerular neutrophil accumulation and renal injury in experimental, crescentic anti-GBM nephritis. These data identify a pathway of neutrophil recruitment within glomerular capillaries following IgG deposition that may be targeted by bosutinib to avert glomerular injury.

Diffuse Extent of Peritubular Capillaritis in Late Antibody-Mediated Rejection: Associations With Levels of Donor-Specific Antibodies and Chronic Allograft Injury.

BACKGROUND: Recently, diffuse peritubular capillaritis (ptc) has been suggested to independently predict chronic transplant injury and loss, and although the ptc score is a diagnostic criterion for antibody-mediated rejection, the utility of diffuse ptc is under debate. METHODS: We evaluated the diagnostic value of ptc characteristics in this cross-sectional study including 85 biopsies of patients with donor-specific antibodies (DSA). Biopsies were reevaluated for the extent (diffuse vs focal), score and leukocytic composition in relation to DSA binding strength (mean fluorescence intensity [MFI]_max). Chronic allograft injury (transplant chronic glomerulopathy [cg] or chronic lesion score CLS]) were associated with ptc features. RESULTS: Peritubular capillaritis was detected in 50% (76% mononuclear ptc). Peritubular capillaritis scores 1, 2, and 3 were present in 36%, 55%, and 9%, and focal or diffuse ptc in 36% or 64%. Diffuse ptc was associated with DSA MFI_max (median: 4407 vs 2419 [focal ptc; P = 0.04] or 1946 [no ptc; P = 0.004]), cg (58% vs no ptc 24% [P = 0.02]), and higher CLS (mean: 6.81 vs 4.67 [focal ptc, P = 0.01] or 5.18 [no ptc, P = 0.001]), respectively. The association of ptc score of 2 or greater with cg was slightly better than with diffuse ptc. Diffuse ptc and ptc score of 2 or greater remained independently related to cg after adjusting for DSA_MFI_max, C4d, or previous rejection episodes, however lost their independent relation after adjusting for total microcirculation scores. Diffuse ptc was the only ptc characteristic independently related to CLS. CONCLUSIONS: Our results emphasize the clinical relevance of reporting diffuse ptc, which may relate to DSA binding strength and potentially to chronic graft injury.

Antineutrophil cytoplasmic antibody-associated glomerulonephritis with immunoglobulin deposition.

BACKGROUND: Antineutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis is commonly classified as pauci-immune glomerulonephritis; however, some cases have granular immunoglobulin deposition along the glomerular capillary. The pathogenesis of immune deposits is poorly studied. METHODS: Of 66 patients diagnosed with ANCA-associated glomerulonephritis on renal biopsy, cases with immunoglobulin deposition along the glomerular capillary were identified and their clinicopathological characteristics were analyzed. We also performed myeloperoxidase (MPO) and double immunofluorescence (IF) stainings to determine the presence of immune complex antigens. RESULTS: Granular IgG deposition, IgG plus IgM deposition, and IgM deposition were observed in 15 (22.1%), 8 (11.2%), and 17 (25.0%) cases, respectively. In cases with granular IgG deposition, MPO-IgG double IF staining revealed co-localization of MPO and IgG. In cases with granular IgM deposition, MPO-IgM double IF staining did not co-localize. By electron microscopy, subepithelial deposition as well as intramembranous, subendothelial, and mesangial deposition was detected in the patients with IgG deposition. In addition, renal survival curves were not significantly different between the immunoglobulin deposition and non-deposition groups. CONCLUSIONS: Granular IgG and/or IgM deposition was observed in 60.6% of patients with ANCA-associated glomerulonephritis. In cases with IgG deposition, electron-dense deposits (EDDs) were observed at various sites in the glomerulus, and MPO and IgG immunocomplex deposition was frequently observed along the glomerular capillary. With IgM deposition, EDDs were not obvious in the glomerular basement membrane, and MPO and IgM immunocomplex was not detected. These data suggest differential mechanism between IgG deposition and IgM deposition.

Patrolling monocytes promote intravascular neutrophil activation and glomerular injury in the acutely inflamed glomerulus.

Nonclassical monocytes undergo intravascular patrolling in blood vessels, positioning them ideally to coordinate responses to inflammatory stimuli. Under some circumstances, the actions of monocytes have been shown to involve promotion of neutrophil recruitment. However, the mechanisms whereby patrolling monocytes control the actions of neutrophils in the circulation are unclear. Here, we examined the contributions of monocytes to antibody- and neutrophil-dependent inflammation in a model of in situ immune complex-mediated glomerulonephritis. Multiphoton and spinning disk confocal intravital microscopy revealed that monocytes patrol both uninflamed and inflamed glomeruli using ß2 and α4 integrins and CX3CR1. Monocyte depletion reduced glomerular injury, demonstrating that these cells promote inappropriate inflammation in this setting. Monocyte depletion also resulted in reductions in neutrophil recruitment and dwell time in glomerular capillaries and in reactive oxygen species (ROS) generation by neutrophils, suggesting a role for cross-talk between monocytes and neutrophils in induction of glomerulonephritis. Consistent with this hypothesis, patrolling monocytes and neutrophils underwent prolonged interactions in glomerular capillaries, with the duration of these interactions increasing during inflammation. Moreover, neutrophils that interacted with monocytes showed increased retention and a greater propensity for ROS generation in the glomerulus. Also, renal patrolling monocytes, but not neutrophils, produced TNF during inflammation, and TNF inhibition reduced neutrophil dwell time and ROS production, as well as renal injury. These findings show that monocytes and neutrophils undergo interactions within the glomerular microvasculature. Moreover, evidence indicates that, in response to an inflammatory stimulus, these interactions allow monocytes to promote neutrophil recruitment and activation within the glomerular microvasculature, leading to neutrophil-dependent tissue injury.

Does asymptomatic recurrent diffuse capillary C4d complement deposition impair cardiac allograft function?

BACKGROUND: The aim of this study was to evaluate whether asymptomatic recurrent (≥2) antibody-mediated rejection (pAMR 1+), defined as diffuse capillary C4d immunostaining (rAMR) on endomyocardial biopsies (EMBs), during the first year after heart transplantation impairs left ventricular (LV) function. METHODS: Fifty-four consecutive heart transplant patients who survived well (New York Heart Association ≤2 and EF≥55%) the first month after transplantation were enrolled and prospectively underwent 490 echocardiographies and EMB. Asymptomatic rAMR without histopathologic findings was evaluated as a risk factor for deterioration of graft function. Primary endpoint, assessed 1 year after transplantation, was development of LV dysfunction and/or adverse remodeling according to pre-specified echo parameters. RESULTS: During the first year from transplantation, rAMR occurred in five patients. Recurrent AMR was associated with a significant higher risk to develop LV concentric hypertrophy (OR 3.6, 95% CI: 1.8-7.0, P=.02) or reduced lateral S' peak velocity (OR 2.3, 95% CI: 1.5-3.6, P=.03). Patients with rAMR showed significative adverse graft remodeling (ΔLV end-diastolic volume: +16±12.3 vs -0.2±14.4 mL; P=.02) and deterioration of graft function (Δlateral S' peak velocity: -3.3±3 vs -0.4±2.9 cm/s; P=.03). CONCLUSIONS: Recurrent asymptomatic diffuse capillary C4d immunostaining may play a role in the early development of cardiac allograft adverse remodeling and dysfunction.

The prognostic values of caveolin-1 immunoreactivity in peritubular capillaries in patients with kidney transplantation.

The low sensitivity of C4d immunoreactivity in peritubular capillaries (PTCs) hinders its use in the diagnosis of chronic active antibody-mediated rejection (CAAMR). C4d-negative CAAMR was defined in the 2013 Banff classification, which included the expression of endothelial-associated transcripts (ENDATs). We previously showed that the ENDAT caveolin-1 (CAV-1) is a distinct feature of CAAMR. In this study, we investigated the prognostic value of CAV-1 immunoreactivity in PTCs in kidney transplant patients. Ninety-eight kidney transplant recipients were included in this study. The prognostic value of CAV-1 immunoreactivity in PTCs was evaluated by double immunostaining for CAV-1 and pathologische Anatomie Leiden endothelium (PAL-E, a PTC marker) in the PTCs of kidney allograft biopsy samples. The patients were divided into two groups: CAV-1/PAL-E<50% and CAV-1/PAL-E≥50%. Kaplan-Meier curves showed that CAV-1/PAL-E≥50% patients had a significantly worse prognosis than that of CAV-1/PAL-E<50% patients (log-rank; P<.001). C4d staining of PTCs was not associated with the development of graft failure (log-rank; P=.345), whereas in a multivariate Cox regression analysis, CAV-1 immunoreactivity in PTCs was independently associated with graft failure (hazard ratio: 11.1; P=.0324). CAV-1 immunoreactivity in PTCs may serve as a prognostic marker for kidney allograft survival.

Pathological implications of linear immunoglobulin G staining on the glomerular capillary walls in a case of infection-related glomerulonephritis.

We report a 32-year-old man with nephrotic syndrome and preceding symptom of infection. He had renal insufficiency, hypocomplementemia, and elevated titer of anti-streptolysin O. Renal biopsy showed mesangial hypercellularity and focal segmental endocapillary hypercellularity with double contour of the glomerular basement membrane (GBM). Immunofluorescence study showed granular C3 staining on the mesangial areas and glomerular capillary walls (GCWs) and linear immunoglobulin G (IgG) staining on GCWs. Electron microscopy revealed sporadic subepithelial humps, discontinuous small and thin deposits in the endothelial side of the GBM and mesangial deposits. He was diagnosed with infection-related glomerulonephritis (IRGN) with the striking finding of linear IgG staining, which is unusual in IRGN. The patient did not have diabetes mellitus or anti-GBM disease. The patient's serum seemed not to contain IgG, which can bind to GCW. He showed normalization of complement within two months after relief from infection symptoms and a trend toward improvement in proteinuria, hematuria and renal function over 14 months. We discuss the possible mechanisms of linear IgG staining in our case based on clinical and experimental studies on IRGN with cationic bacterial protein as antigen.

Reviewing the pathogenesis of antibody-mediated rejection and renal graft pathology after kidney transplantation.

The clinicopathological context of rejection after kidney transplantation was well recognized. Banff conferences greatly contributed to elucidate the pathogenesis and to establish the pathologic criteria of rejection after kidney transplantation. The most important current problem of renal transplantation is de novo donor-specific antibody (DSA) production leading chronic rejection and graft loss. Microvascular inflammation is considered as a reliable pathological marker for antibody-mediated rejection (AMR) in the presence of DSA. Electron microscopic study allowed us to evaluate early changes in peritubular capillaries in T-lymphocyte mediated rejection and transition to antibody-mediated rejection. Severe endothelial injuries with edema and activated lymphocyte invaded into subendothelial space with early multi-layering of peritubular capillary basement membrane suggest T-lymphocyte mediated rejection induce an unbounded chain of antibody-mediated rejection. The risk factors of AMR after ABO-incompatible kidney transplantation are important issues. Anti-ABO blood type antibody titre of IgG excess 32-fold before transplant operation is the only predictable factor for acute AMR. Characteristics of chronic active antibody-mediated rejection (CAAMR) are one of the most important problems. Light microscopic findings and C4d stain of peritubular capillary and glomerular capillary are useful diagnostic criteria of CAAMR. Microvascular inflammation, double contour of glomerular capillary and thickening of peritubular capillary basement are good predictive factors of the presence of de novo DSA. C4d stain of linear glomerular capillary is a more sensitive marker for CAAMR than positive C4d of peritubular capillary. Early and sensitive diagnostic attempts of diagnosing CAAMR are pivotal to prevent chronic graft failure.

Capillary Thrombosis in the Skin: A Pathologic Hallmark of Severe/Chronic Rejection of Human Vascularized Composite Tissue Allografts?

BACKGROUND: Vascularized composite tissue allografts (VCA) can undergo rejection, manifesting pathologically with skin changes that form the basis of the Banff 2007 classification of VCA rejection. METHODS: We have followed 10 human VCA recipients (7 with hand allografts, 3 with face allografts) for pathological signs of rejection. All of them developed episodes of acute rejection. Two patients with hand allografts presented in some of their skin biopsies an as yet unreported pathological finding in human VCA, consisting of capillary thromboses (CT) in the upper dermis. RESULTS: Capillary thrombosis was associated with other typical changes of grade II to III VCA rejection, namely, perivascular T cell infiltrates, but not with vascular C4d deposits (in formalin-fixed tissue). Clinically, the lesions presented as red or violaceous (lichenoid) cutaneous maculopapules. The first patient had several episodes of acute rejection during the 7-year follow-up. The second patient developed donor-specific antibodies; some months after CT were first observed, he developed chronic rejection leading to partial amputation of the allograft. Pathological examination of the skin showed graft vasculopathy and occasional C4d deposits in cutaneous capillaries. CONCLUSIONS: Capillary thrombosis seems to be a novel pathologic finding associated with human VCA rejection. Although its mechanism (immunologic vs nonimmunologic) remains unclear, this finding could carry an unfavorable prognostic significance, prompting close monitoring of the patients for severe/chronic rejection.