Epitope mapping of SARS-CoV-2 RBDs by hydroxyl radical protein footprinting reveals the importance of including negative antibody controls.

Understanding protein-protein interactions is crucial for drug design and investigating biological processes. Various techniques, such as CryoEM, X-ray spectroscopy, linear epitope mapping, and mass spectrometry-based methods, can be employed to map binding regions on proteins. Commonly used mass spectrometry-based techniques are cross-linking and hydrogen­deuterium exchange (HDX). Another approach, hydroxyl radical protein footprinting (HRPF), identifies binding residues on proteins but faces challenges due to high initial costs and complex setups. This study introduces a generally applicable method using Fenton chemistry for epitope mapping in a standard mass spectrometry laboratory. It emphasizes the importance of controls, particularly the inclusion of a negative antibody control, not widely utilized in HRPF epitope mapping. Quantification by TMT labelling is introduced to reduce false positives, enabling direct comparison between sample conditions and biological triplicates. Additionally, six technical replicates were incorporated to enhance the depth of analysis. Observations on the receptor-binding domain (RBD) of SARS-CoV-2 Spike Protein, Alpha and Delta variants, revealed both binding and opening regions. Significantly changed peptides upon mixing with a negative control antibody suggested structural alterations or nonspecific binding induced by the antibody alone. Integration of negative control antibody experiments and high overlap between biological triplicates led to the exclusion of 40% of significantly changed regions. The final identified binding region correlated with existing literature on neutralizing antibodies against RBD. The presented method offers a straightforward implementation for HRPF analysis in a generic mass spectrometry-based laboratory. Enhanced data reliability was achieved through increased technical and biological replicates alongside negative antibody controls.

Trypanosoma brucei Invariant Surface Glycoprotein 75 Is an Immunoglobulin Fc Receptor Inhibiting Complement Activation and Antibody-Mediated Cellular Phagocytosis.

Various subspecies of the unicellular parasite Trypanosoma brucei cause sleeping sickness, a neglected tropical disease affecting millions of individuals and domestic animals. Immune evasion mechanisms play a pivotal role in parasite survival within the host and enable the parasite to establish a chronic infection. In particular, the rapid switching of variant surface glycoproteins covering a large proportion of the parasite's surface enables the parasite to avoid clearance by the adaptive immune system of the host. In this article, we present the crystal structure and discover an immune-evasive function of the extracellular region of the T. brucei invariant surface gp75 (ISG75). Structural analysis determined that the ISG75 ectodomain is organized as a globular head domain and a long slender coiled-coil domain. Subsequent ligand screening and binding analysis determined that the head domain of ISG75 confers interaction with the Fc region of all subclasses of human IgG. Importantly, the ISG75-IgG interaction strongly inhibits both activation of the classical complement pathway and Ab-dependent cellular phagocytosis by competing with C1q and host cell FcγR CD32. Our data reveal a novel immune evasion mechanism of T. brucei, with ISG75 able to inactivate the activities of Abs recognizing the parasite surface proteins.

CD163+ macrophages monitor enhanced permeability at the blood-dorsal root ganglion barrier.

In dorsal root ganglia (DRG), macrophages reside close to sensory neurons and have largely been explored in the context of pain, nerve injury, and repair. However, we discovered that most DRG macrophages interact with and monitor the vasculature by sampling macromolecules from the blood. Characterization of the DRG vasculature revealed a specialized endothelial bed that transformed in molecular, structural, and permeability properties along the arteriovenous axis and was covered by macrophage-interacting pericytes and fibroblasts. Macrophage phagocytosis spatially aligned with peak endothelial permeability, a process regulated by enhanced caveolar transcytosis in endothelial cells. Profiling the DRG immune landscape revealed two subsets of perivascular macrophages with distinct transcriptome, turnover, and function. CD163+ macrophages self-maintained locally, specifically participated in vasculature monitoring, displayed distinct responses during peripheral inflammation, and were conserved in mouse and man. Our work provides a molecular explanation for the permeability of the blood-DRG barrier and identifies an unappreciated role of macrophages as integral components of the DRG-neurovascular unit.

Circulating TREM2 as a noninvasive diagnostic biomarker for NASH in patients with elevated liver stiffness.

BACKGROUND AND AIMS: Reliable noninvasive biomarkers are an unmet clinical need for the diagnosis of NASH. This study investigates the diagnostic accuracy of the circulating triggering receptor expressed on myeloid cells 2 (plasma TREM2) as a biomarker for NASH in patients with NAFLD and elevated liver stiffness. APPROACH AND RESULTS: We collected cross-sectional, clinical data including liver biopsies from a derivation ( n = 48) and a validation cohort ( n = 170) of patients with elevated liver stiffness measurement (LSM ≥ 8.0 kPa). Patients with NAFLD activity scores (NAS) ≥4 were defined as having NASH. Plasma TREM2 levels were significantly elevated in patients with NASH of the derivation cohort, with an area under the receiver operating characteristics curve (AUROC) of 0.92 (95% confidence interval [CI], 0.84-0.99). In the validation cohort, plasma TREM2 level increased approximately two-fold in patients with NASH, and a strong diagnostic accuracy was confirmed (AUROC, 0.83; 95% CI, 0.77-0.89; p < 0.0001). Plasma TREM2 levels were associated with the individual histologic features of NAS: steatosis, lobular inflammation, and ballooning ( p < 0.0001), but only weakly with fibrosis stages. Dual cutoffs for rule-in and rule-out were explored: a plasma TREM2 level of ≤38 ng/ml was found to be an optimal NASH rule-out cutoff (sensitivity 90%; specificity 52%), whereas a plasma TREM2 level of ≥65 ng/ml was an optimal NASH rule-in cutoff (specificity 89%; sensitivity 54%). CONCLUSIONS: Plasma TREM2 is a plausible individual biomarker that can rule-in or rule-out the presence of NASH with high accuracy and thus has the potential to reduce the need for liver biopsies and to identify patients who are eligible for clinical trials in NASH.

Obese Patients With Nonalcoholic Fatty Liver Disease Have an Increase in Soluble Plasma CD163 and a Concurrent Decrease in Hepatic Expression of CD163.

Background and Aims: Macrophages play an important role in the development of nonalcoholic fatty liver disease (NAFLD) and its progression to nonalcoholic steatohepatitis (NASH). In this study, we investigated the hepatic expression of the macrophage scavenger receptor CD163 and the plasma level of its shed soluble form (sCD163) in patients with obesity and NASH, non-NASH NAFLD (NAFL), or healthy livers (no NAFLD). Methods: Paired liver biopsies and plasma samples were collected from 61 patients with obesity (body mass index ≥35). Hepatic expression of CD163 was analyzed by immunohistochemistry and data-independent acquisition mass spectrometry, whilst plasma levels of sCD163 were determined by enzyme-linked immunosorbent assay and data-independent acquisition mass spectrometry. NAFLD stage and activity were assessed using the Kleiner fibrosis and NASH Clinical Research Network (NAS-CRN) scoring system. Results: sCD163 turned out as a promising predictor of NASH with an area under the receiver-operating characteristic curve of 0.78 [0.65;0.92] (P = .0008). sCD163 increased with more severe NAFLD both in univariate (odds ratio [OR] = 3.31[1.80;6.11], P < .001) and multivariable ordinal logistic regression adjusting for NAFLD risk factors (OR = 2.02 [1.03;3.97], P = .042). On the other hand, hepatic expression of CD163 was negatively associated with more severe NAFLD in univariate ordinal logistic regression determined by immunohistochemistry (OR = 0.91[0.84;0.98], P = .015) and proteomics (OR = 0.13[0.02;0.80], P = .028). Taking NAFLD risk factors into account, hepatic expression of CD163 was only associated with the fibrosis stage (OR = 0.01 [0.0003;0.21], P = .004). Accordingly, hepatic CD163 surface expression and sCD163 were negatively correlated (rho = -0.478, P = .0001). Conclusion: An increased plasma sCD163 and a concurrent decreased hepatic expression of CD163 are strongly associated with NAFLD in obese patients.

Haptoglobin-related protein in human plasma correlates to haptoglobin concentrations and phenotypes.

Haptoglobin-related protein (Hpr) is a plasma protein with high sequence similarity to haptoglobin (Hp). Like Hp, Hpr also binds hemoglobin (Hb) with high affinity, but it does not bind to the Hb-Hp receptor CD163 on macrophages. The Hpr concentration is markedly lower than Hp in plasma and its regulation is not understood. In the present study, we have developed non-crossreactive antibodies to Hpr to analyze the Hpr concentration in 112 plasma samples from anonymized individuals and compared it to Hp. The results show that plasma Hpr correlated with Hp concentrations (rho = 0.46, p = .0001). Hpr accounts for on average 0.35% of the Hp/Hpr pool but up to 29% at low Hp levels. Furthermore, the Hpr concentrations were significantly lower in individuals with the Hp2-2 phenotype compared to those with the Hp2-1 or Hp1-1 phenotypes. Experimental binding analysis did not provide evidence that Hpr associates with Hp and in this way is removed via CD163. In conclusion, the Hpr concentration correlates to Hp concentrations and Hp-phenotypes by yet unknown mechanisms independent of CD163-mediated removal of Hb-Hp complexes.

Re-evalution of the measurement of haptoglobin in human plasma samples.

Haptoglobin (Hp) is an abundant plasma protein scavenging hemoglobin (Hb) via CD163 on macrophages. This process consumes Hp, which therefore negatively correlates to hemolysis. However, exact measurements of Hp plasma levels are complicated by different phenotypes (Hp1-1, Hp2-1, and Hp2-2) forming different oligomeric states with differences in immunoreactivity. In addition, humans have an immune-cross-reactive Hp-related protein. In the present study, we developed Hp-specific monoclonal antibodies for an accurate Hp analysis of the different Hp phenotypes in a panel of 112 anonymous samples from hospitalized individuals subjected to routine Hp immunoturbidimetric measurements. The data revealed immunoturbidimetry as a reliable method in most cases but also that the use of non-phenotype-specific calibrators leads to substantial bias in the measurement of the Hp-concentration, non at least in Hp1-1 individuals. Furthermore, analysis of the Hb-dependence of the CD163 interaction with Hp1-1 and Hp2-2 showed that a higher 'cost-effectiveness' in the consumption of dimeric Hp1-1 versus multimeric Hp phenotypes is a likely contribution to the observed differences in the plasma levels of the Hp phenotypes. In conclusion, the determination of Hp phenotype and the use of phenotype-specific calibrators are essential to obtain a precise estimate of the Hp level in healthy and diseased individuals.

Retroviral glycoprotein-mediated immune suppression via the potassium channel KCa3.1 - A new strategy for amelioration of inflammatory bowel diseases.

Peptides derived from retroviral envelope proteins have been shown to possess a wide range of immunosuppressive and anti-inflammatory activities. We have previously reported identification of such a peptide derived from the envelope protein coded by a human endogenous retrovirus (HERV). In this study, we identify that in vitro the peptide inhibits the KCa3.1 potassium channel, a potential target for therapy of immune diseases. We describe in vitro ENV59-GP3 effects with respect to potency of inhibition on KCa3.1 channels and calcium influx. Furthermore, we asses in vivo the effect of blocking KCa3.1 with ENV59-GP3 peptide or KCa3.1-blocker NS6180 on protection against DSS-induced acute colitis. ENV59-GP3 peptide treatment showed reduction of the disease score in the DSS-induced acute colitis mice model, which was comparable to effects of the KCa3.1 channel blocker NS6180. Analysis of cytokine production from DSS-mice model treated animals revealed equipotent inhibitory effects of the ENV59-GP3 and NS6180 compounds on the production of IL-6, TNF-α, IL-1ß. These findings altogether suggest that ENV59-GP3 functions as a KCa3.1 channel inhibitor and underline the implications of using virus derived channel blockers for treatment of autoimmune diseases. Additionally, they open the possibilities whether KCa3.1 inhibition is efficacious in patients with inflammatory bowel diseases.

Plasma Kallikrein Cleaved H-kininogen: An End-Point Marker for Contact Activation in vitro and ex vivo.

Objectives: The contact system consists of coagulation factor XII (FXII), prekallikrein, and H-kininogen (HK) and plays important roles in many diseases. Plasma kallikrein (PKa) cleaved HK (cHK) is a marker of contact activation. Presently, we developed a specific and precise enzyme-linked immunosorbent assay (ELISA) for determination of cHK in vitro and ex vivo. Methods: Cleaved HK specific mouse monoclonal antibodies (mAbs) were generated using a peptide corresponding to the PKa cleavage site on HK as immunogen. ELISA, surface plasmon resonance analysis, and immunoprecipitation established the specificity of the antibody, which subsequently was used in a sandwich ELISA. The analytical imprecision and the concentration of cHK in a reference population and in women receiving oral contraceptives (OC) were determined. cHK was assessed in vitro in plasma exposed to polytetrafluoroethylene, silicone, and glass tubes. Results: The selected mAb showed excellent specificity towards cHK. The intra-assay and inter-assay CV of the ELISA were 3.6 and 6.0%, respectively. The reference population (60 women, 60 men) displayed a median cHK plasma concentration of 1.38 µg/mL and a reference interval of 0.82 - 2.56 µg/mL. Women receiving OC had significantly higher concentrations, p < 0.001. cHK was significantly elevated in plasma exposed to polytetrafluoroethylene, p = 0.001, and glass, p < 0.0001. Conclusion: The ELISA showed excellent precision and specificity. cHK assessment ex vivo demonstrated ongoing contact activation in healthy individuals, augmented by OC. The cHK antibody and the ELISA could be promising tools in contact activation related diseases and in vitro investigations of the plasma compatibility of blood contacting biomaterials.

Soluble CD163 Changes Indicate Monocyte Association With Cognitive Deficits in Parkinson's Disease.

BACKGROUND: Parkinson's disease (PD) is a neurodegenerative disorder with a significant immune component, as demonstrated by changes in immune biomarkers in patients' biofluids. However, which specific cells are responsible for those changes is unclear because most immune biomarkers can be produced by various cell types. OBJECTIVES: The aim of this study was to explore monocyte involvement in PD. METHODS: We investigated the monocyte-specific biomarker sCD163, the soluble form of the receptor CD163, in cerebrospinal fluid (CSF) and serum in two experiments, and compared it with other biomarkers and clinical data. Potential connections between CD163 and alpha-synuclein were studied in vitro. RESULTS: CSF-sCD163 increased in late-stage PD and correlated with the PD biomarkers alpha-synuclein, Tau, and phosphorylated Tau, whereas it inversely correlated with the patients' cognitive scores, supporting monocyte involvement in neurodegeneration and cognition in PD. Serum-sCD163 increased only in female patients, suggesting a sex-distinctive monocyte response. CSF-sCD163 also correlated with molecules associated with adaptive and innate immune system activation and with immune cell recruitment to the brain. Serum-sCD163 correlated with proinflammatory cytokines and acute-phase proteins, suggesting a relation to chronic systemic inflammation. Our in vitro study showed that alpha-synuclein activates macrophages and induces shedding of sCD163, which in turn enhances alpha-synuclein uptake by myeloid cells, potentially participating in its clearance. CONCLUSIONS: Our data present sCD163 as a potential cognition-related biomarker in PD and suggest a role for monocytes in both peripheral and brain immune responses. This may be directly related to alpha-synuclein's proinflammatory capacity but could also have consequences for alpha-synuclein processing. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Complement activation in human autoimmune diseases and mouse models; employing a sandwich immunoassay specific for C3dg.

In human autoimmune diseases, low plasma levels of complement factors C3 and C4 are commonly used as a proxy for complement activation. The measurements of C3 and C4 concentrations (the result of synthesis and consumption) however, show low sensitivity in patient follow-up. We find that the estimation of the C3dg fragment released during complement activation is a better parameter for complement activation. Available techniques for measuring the activation fragment C3dg, e.g. immune-electrophoresis or involving PEG-precipitation, are time-consuming and difficult to standardize. Here we examine the specificity and use of an antibody with mono-specificity for a neoepitope at the N-terminus of C3dg, which is only exposed after cleavage of C3. We present a stable, reproducible, and easy-to-use, time-resolved immunoassay with specificity for C3dg that can be used to directly evaluate ongoing complement activation. We demonstrate that the assay can be applied to clinical samples with a high specificity (95%) and a positive likelihood ratio of 10. It can also differentiate the complement related disease Systemic Lupus Erythematosus from controls and other immune-mediatedimmune mediated diseases like Rheumatoid Arthritis (86% specificity) and Spondyloarthritis (91% specificity). Further, we establish how the assay may also be used for experimental research in in vivo mouse models.

Targeting of CD163+ Macrophages in Inflammatory and Malignant Diseases.

The macrophage is a key cell in the pro- and anti-inflammatory response including that of the inflammatory microenvironment of malignant tumors. Much current drug development in chronic inflammatory diseases and cancer therefore focuses on the macrophage as a target for immunotherapy. However, this strategy is complicated by the pleiotropic phenotype of the macrophage that is highly responsive to its microenvironment. The plasticity leads to numerous types of macrophages with rather different and, to some extent, opposing functionalities, as evident by the existence of macrophages with either stimulating or down-regulating effect on inflammation and tumor growth. The phenotypes are characterized by different surface markers and the present review describes recent progress in drug-targeting of the surface marker CD163 expressed in a subpopulation of macrophages. CD163 is an abundant endocytic receptor for multiple ligands, quantitatively important being the haptoglobin-hemoglobin complex. The microenvironment of inflammation and tumorigenesis is particular rich in CD163+ macrophages. The use of antibodies for directing anti-inflammatory (e.g., glucocorticoids) or tumoricidal (e.g., doxorubicin) drugs to CD163+ macrophages in animal models of inflammation and cancer has demonstrated a high efficacy of the conjugate drugs. This macrophage-targeting approach has a low toxicity profile that may highly improve the therapeutic window of many current drugs and drug candidates.

Contact activation-induced complex formation between complement factor H and coagulation factor XIIa.

BACKGROUND: The complement and coagulation systems share an evolutionary origin with many components showing structural homology. Certain components, including complement factor H (FH) and coagulation factor XII (FXII), have separately been shown to have auxiliary activities across the two systems. OBJECTIVES: The interaction between FXII and FH was investigated. METHODS: Using enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR) complex formation between different FXII forms and FH was investigated. The presence of α-FXIIa:FH complexes upon contact activation in plasma was evaluated by ELISA and immunoprecipitation. RESULTS: We identified and characterized a direct interaction between the components and demonstrated that among different forms of FXII, only the activated α-FXIIa formed complexes with FH, with an apparent binding strength Kd of 34 ± 9 nmol/L. The complex formation involved the kringle domain of the heavy chain of FXII. C1-inhibitor induced inhibition of α-FXIIa did not alter the binding of α-FXIIa toward FH. We further demonstrated the presence of α-FXIIa:FH complexes in normal human plasma upon contact activation, indicating formation of α-FXIIa:FH complexes as a consequence of α-FXIIa generation. Complex formation between α-FXIIa and FH was also assessed in hereditary angioedema (HAE) patients with C1-inhibitor deficiency as well as rheumatoid arthritis (RA) patients with high levels of anti-cyclic citrullinated peptide (anti-CCP) upon contact activation. We observed elevated levels of α-FXIIa:FH complexes in HAE patients, and equal levels of complexes in RA patients and healthy individuals upon contact activation. CONCLUSION: A direct interaction between α-FXIIa and FH is demonstrated. Our findings represent a new crosstalk between these systems, potentially important in the onset and pathology of inflammatory vascular diseases.

Specific targeting of CD163+ TAMs mobilizes inflammatory monocytes and promotes T cell-mediated tumor regression.

Tumor-associated macrophages (TAMs) play critical roles in tumor progression but are also capable of contributing to antitumor immunity. Recent studies have revealed an unprecedented heterogeneity among TAMs in both human cancer and experimental models. Nevertheless, we still understand little about the contribution of different TAM subsets to tumor progression. Here, we demonstrate that CD163-expressing TAMs specifically maintain immune suppression in an experimental model of melanoma that is resistant to anti-PD-1 checkpoint therapy. Specific depletion of the CD163+ macrophages results in a massive infiltration of activated T cells and tumor regression. Importantly, the infiltration of cytotoxic T cells was accompanied by the mobilization of inflammatory monocytes that significantly contributed to tumor regression. Thus, the specific targeting of CD163+ TAMs reeducates the tumor immune microenvironment and promotes both myeloid and T cell-mediated antitumor immunity, illustrating the importance of selective targeting of tumor-associated myeloid cells in a therapeutic context.

Using the hemoglobin-binding Staphylococcus aureus protein IsdH to enable plasma analysis of hemolyzed blood samples.

Background Intravascular hemolysis and in vitro hemolysis are prevalent contributors to failed blood sample analysis in the routine hospital laboratory. Interferences by hemoglobin in spectrophotometric and certain enzyme activity assays is the major causative factor. Methods By exploiting the hemoglobin-binding properties of the iron-regulated surface determinant H (IsdH) protein from Staphylococcus aureus we have developed a new method to instantly remove hemoglobin and hemoglobin-haptoglobin complexes from plasma in vitro thereby enabling the measurement of hemoglobin-sensitive analytes in hemolyzed plasma. In the present study we used an engineered IsdH mutant form conjugated to Sepharose for the efficient removal of plasma hemoglobin in concentrations up to 15 mg/mL. The high abundance of haptoglobin, which forms a tight complex with hemoglobin in plasma, did not affect the hemoglobin removal by IsdH Sepharose. Results Applying the method on plasma samples that beforehand were spiked with blood hemolysate re-enabled measurement of the hemolysis sensitive parameters: alkaline phosphatase, conjugated bilirubin, iron, ferritin, γ-glutamyltransferase, total thyroxine and troponin T. IsdH Sepharose-mediated hemoglobin removal also enabled measurement of hemolysis sensitive parameters in hemolyzed samples from anonymized patients. Conclusions In conclusion, IsdH Sepharose is a simple cost-effective pretreatment of hemolyzed samples correcting and enabling the measurement of several important hemoglobin-sensitive parameters in a way compatible with standard procedures in routine laboratories.

Immunomodulating peptides derived from different human endogenous retroviruses (HERVs) show dissimilar impact on pathogenesis of a multiple sclerosis animal disease model.

Retroviruses including Human Endogenous Retroviruses (HERVs), contain a conserved region with highly immunomodulatory functions in the transmembrane proteins in envelope gene (env) named immunosuppressive domain (ISU). In this report, we demonstrate that Env59-GP3 peptide holds therapeutic potential in a mouse model of myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE). The results show that this specific HERV-H derived ISU peptide, but not peptide derived from another env gene HERV-K, decreased the development of EAE in C57BL/6 mice, accompanied by reduced demyelination and inhibition of inflammatory cells. Moreover, here we tested the effect of peptides on macrophages differentiation. The treatment with Env59-GPS peptide modulate the pro-inflammatory M1 profile and anti-inflammatory M2 macrophages, being shown by inhibiting inflammatory M1 hallmark genes/cytokines expression and enhancing expression of M2 associated markers. These results demonstrate that Env59-GP3 ISU peptide has therapeutic potential in EAE possibly through inducing the polarization of M2 macrophages and inhibiting inflammatory responses.

The Staphylococcus aureus Protein IsdH Inhibits Host Hemoglobin Scavenging to Promote Heme Acquisition by the Pathogen.

Hemolysis is a complication in septic infections with Staphylococcus aureus, which utilizes the released Hb as an iron source. S. aureus can acquire heme in vitro from hemoglobin (Hb) by a heme-sequestering mechanism that involves proteins from the S. aureus iron-regulated surface determinant (Isd) system. However, the host has its own mechanism to recapture the free Hb via haptoglobin (Hp) binding and uptake of Hb-Hp by the CD163 receptor in macrophages. It has so far remained unclear how the Isd system competes with this host iron recycling system in situ to obtain the important nutrient. By binding and uptake studies, we now show that the IsdH protein, which serves as an Hb receptor in the Isd system, directly interferes with the CD163-mediated clearance by binding the Hb-Hp complex and inhibiting CD163 recognition. Analysis of truncated IsdH variants including one or more of three near iron transporter domains, IsdHN1, IsdHN2, and IsdHN3, revealed that Hb binding of IsdHN1 and IsdHN2 accounted for the high affinity for Hb-Hp complexes. The third near iron transporter domain, IsdHN3, exhibited redox-dependent heme extraction, when Hb in the Hb-Hp complex was in the oxidized met form but not in the reduced oxy form. IsdB, the other S. aureus Hb receptor, failed to extract heme from Hb-Hp, and it was a poor competitor for Hb-Hp binding to CD163. This indicates that Hb recognition by IsdH, but not by IsdB, sterically inhibits the receptor recognition of Hb-Hp. This function of IsdH may have an overall stimulatory effect on S. aureus heme acquisition and growth.

Anti-CD163-dexamethasone conjugate inhibits the acute phase response to lipopolysaccharide in rats.

AIM: To study the effect of a new anti-CD163-dexamethasone conjugate targeting activated macrophages on the hepatic acute phase response in rats. METHODS: Wistar rats were injected intravenous with either the CD163 targeted dexamethasone-conjugate (0.02 mg/kg) or free dexamethasone (0.02 or 1 mg/kg) 24 h prior to lipopolysaccharide (LPS) (2.5 mg/kg intraperitoneal). We measured plasma concentrations of tumour necrosis factor-α (TNF-α) and interleukin 6 (IL-6) 2 h post-LPS and liver mRNAs and serum concentrations of the rat acute phase protein α-2-macroglobulin (α-2-M) 24 h after LPS. Also, plasma concentrations of alanine aminotransferase and bilirubin were measured at termination of the study. Spleen weight served as an indicator of systemic steroid effects. RESULTS: The conjugate halved the α-2-M liver mRNA (3.3 ± 0.6 vs 6.8 ± 1.1, P < 0.01) and serum protein (201 ± 48 µg/mL vs 389 ± 67 µg/mL, P = 0.04) after LPS compared to low dose dexamethasone treated animals, while none of the free dexamethasone doses had an effect on liver mRNA or serum levels of α-2-M. Also, the conjugate reduced TNF-α (7208 ± 1977 pg/mL vs 21583 ± 7117 pg/mL, P = 0.03) and IL-6 (15685 ± 3779 pg/mL vs 25715 ± 4036 pg/mL, P = 0.03) compared to the low dose dexamethasone. The high dose dexamethasone dose decreased the spleen weight (421 ± 11 mg vs 465 ± 12 mg, P < 0.05) compared to controls, an effect not seen in any other group. CONCLUSION: Low-dose anti-CD163-dexamethasone conjugate effectively decreased the hepatic acute phase response to LPS. This indicates an anti-inflammatory potential of the conjugate in vivo.

Anti-CD163-dexamethasone protects against apoptosis after ischemia/reperfusion injuries in the rat liver.

AIM: The Pringle maneuver is a way to reduce blood loss during liver surgery. However, this may result in ischemia/reperfusion injury in the development of which Kupffer cells play a central role. Corticosteroids are known to have anti-inflammatory effects. Our aim was to investigate whether a conjugate of dexamethasone and antibody against the CD163 macrophage cell surface receptor could reduce ischemia/reperfusion injury in the rat liver. METHODS: Thirty-six male Wistar rats were used for the experiments. Animals were randomly divided into four groups of eight receiving anti-CD163-dexamethasone, high dose dexamethasone, low dose dexamethasone or placebo intravenously 18 h before laparotomy with subsequent 60 min of liver ischemia. After reperfusion for 24 h the animals had their liver removed. Bloods were drawn 30 min and 24 h post ischemia induction. Liver cell apoptosis and necrosis were analyzed by stereological quantification. RESULTS: After 24 h' reperfusion, the fraction of cell in non-necrotic tissues exhibiting apoptotic profiles was significantly lower in the high dose dexamethasone (p = 0.03) and anti-CD163-dex (p = 0.03) groups compared with the low dose dexamethasone and placebo groups. There was no difference in necrotic cell volume between groups. After 30 min of reperfusion, levels of haptoglobin were significantly higher in the anti-CD163-dex and high dose dexamethasone groups. Alanine aminotransferase and alkaline phosphatase were significantly higher in the high dose dexamethasone group compared to controls after 24 h' reperfusion. CONCLUSIONS: We show that pharmacological preconditioning with anti-CD163-dex and high dose dexamethasone reduces the number of apoptotic cells following ischemia/reperfusion injury.

Drug Trafficking into Macrophages via the Endocytotic Receptor CD163.

In inflammatory diseases, macrophages are a main producer of a range of cytokines regulating the inflammatory state. This also includes inflammation induced by tumor growth, which recruits so-called tumor-associated macrophages supporting tumor growth. Macrophages are therefore relevant targets for cytotoxic or phenotype-modulating drugs in the treatment of inflammatory and cancerous diseases. Such targeting of macrophages has been tried using the natural propensity of macrophages to non-specifically phagocytose circulating foreign particulate material. In addition, the specific targeting of macrophage-expressed receptors has been used in order to obtain a selective uptake in macrophages and reduce adverse effects of off-target delivery of drugs. CD163 is a highly expressed macrophage-specific endocytic receptor that has been studied for intracellular delivery of small molecule drugs to macrophages using targeted liposomes or antibody drug conjugates. This review will focus on the biology of CD163 and its potential role as a target for selective macrophage targeting compared with other macrophage targeting approaches.