Point-of-care neutrophil and monocyte surface markers differentiate bacterial from viral infections at the emergency department within 30 min

Rapid discrimination between viral and bacterial infections in a point-of-care setting will improve clinical outcome. Expression of CD64 on neutrophils (neuCD64) increases during bacterial infections, whereas expression of CD169 on classical monocytes (cmCD169) increases during viral infections. The diagnostic value of automated point-of-care neuCD64 and cmCD169 analysis was assessed for detecting bacterial and viral infections at the emergency department. Additionally, their value as input for machine learning models was studied. A prospective observational cohort study in patients suspected of infection was performed at an emergency department. A fully automated point-of-care flow cytometer measured neuCD64, cmCD169, and additional leukocyte surface markers. Flow cytometry data were gated using the FlowSOM algorithm. Bacterial and viral infections were assessed in standardized clinical care. The sole and combined diagnostic value of the markers was investigated. Clustering based on unsupervised machine learning identified unique patient clusters. Eighty-six patients were included. Thirty-five had a bacterial infection, 30 had a viral infection, and 21 had no infection. neuCD64 was increased in bacterial infections (P < 0.001), with an area under the receiver operating characteristic curve (AUROC) of 0.73. cmCD169 was higher in virally infected patients (P < 0.001; AUROC 0.79). Multivariate analyses incorporating additional markers increased the AUROC for bacterial and viral infections to 0.86 and 0.93, respectively. The additional clustering identified 4 distinctive patient clusters based on infection type and outcome. Automated neuCD64 and cmCD169 determination can discriminate between bacterial and viral infections. These markers can be determined within 30 min, allowing fast infection diagnostics in the acute clinical setting.

Development of an explainable AI system using routine clinical parameters for rapid differentiation of inflammatory conditions

Introduction

Inflammatory conditions in patients have various causes and require different treatments. Bacterial infections are treated with antibiotics, while these medications are ineffective against viral infections. Autoimmune diseases and graft-versus-host disease (GVHD) after allogeneic stem cell transplantation, require immunosuppressive therapies such as glucocorticoids, which may be contraindicated in other inflammatory states. In this study, we employ a combination of straightforward blood tests to devise an explainable artificial intelligence (XAI) for distinguishing between bacterial infections, viral infections, and autoimmune diseases/graft-versus-host disease.

Patients and methods

We analysed peripheral blood from 80 patients with inflammatory conditions and 38 controls. Complete blood count, CRP analysis, and a rapid flow cytometric test for myeloid activation markers CD169, CD64, and HLA-DR were utilized. A two-step XAI distinguished firstly with C5.0 rules pruned by ABC analysis between controls and inflammatory conditions and secondly between the types of inflammatory conditions with a new bivariate decision tree using the Simpson impurity function.

Results

Inflammatory conditions were distinguished using an XAI, achieving an overall accuracy of 81.0% (95%CI 72 - 87%). Bacterial infection (N = 30), viral infection (N = 26), and autoimmune diseases/GVHD (N = 24) were differentiated with accuracies of 90.3%, 80.0%, and 79.0%, respectively. The most critical parameter for distinguishing between controls and inflammatory conditions was the expression of CD64 on neutrophils. Monocyte count and expression of CD169 were most crucial for the classification within the inflammatory conditions.

Conclusion

Treatment decisions for inflammatory conditions can be effectively guided by XAI rules, straightforward to implement and based on promptly acquired blood parameters.

Elevated CD169 expressing monocyte/macrophage promotes systemic inflammation and disease progression in cirrhosis

Systemic inflammation is related to disease progression and prognosis in patients with advanced cirrhosis. However, the mechanisms underlying the initiation of inflammation are still not fully understood. The role of CD169+ monocyte/macrophage in cirrhotic systemic inflammation was undetected. Flow cytometry analysis was used to detect the percentage and phenotypes of CD169+ monocytes as well as their proinflammatory function in patient-derived cirrhotic tissue and blood. Transcriptome differences between CD169+ and CD169- monocytes were also compared. Additionally, a mouse model with specific depletion of CD169+ monocytes/macrophages was utilized to define their role in liver injury and fibrosis. We observed increased CD169 expression in monocytes from cirrhotic patients, which was correlated with inflammatory cytokine production and disease progression. CD169+ monocytes simultaneously highly expressed M1- and M2-like markers and presented immune-activated profiles. We also proved that CD169+ monocytes robustly prevented neutrophil apoptosis. Depletion of CD169+ monocytes/macrophages significantly inhibited inflammation and liver necrosis in acute liver injury, but the spontaneous fibrin resolution after repeated liver injury was impaired. Our results indicate that CD169 defines a subset of inflammation-associated monocyte that correlates with disease development in patients with cirrhosis. This provides a possible therapeutic target for alleviating inflammation and improving survival in cirrhosis.

Targeted delivery of herpes simplex virus glycoprotein D to CD169+ macrophages using ganglioside liposomes alleviates herpes simplex keratitis in mice

Herpes simplex keratitis (HSK) is a common blinding corneal disease caused by herpes simplex virus type 1 (HSV-1) infection. Antiviral drugs and corticosteroids haven't shown adequate therapeutic efficacy. During the early stage of HSV-1 infection, macrophages serve as the first line of defense. In particular, CD169+ macrophages play an important role in phagocytosis and antigen presentation. Therefore, we constructed GM-gD-lip, a ganglioside GM1 liposome vaccine encapsulating HSV-1 glycoprotein D and targeting CD169+ macrophages. After subconjunctival injection of the vaccine, we evaluated the survival rate and ocular surface lesions of the HSK mice, as well as the virus levels in the tear fluid, corneas, and trigeminal ganglia. We discovered that GM-gD-lip reduced HSV-1 viral load and alleviated the clinical severity of HSK. The GM-gD-lip also increased the number of corneal infiltrating macrophages, especially CD169+ macrophages, and polarized them toward M1. Furthermore, the number of dendritic cells (DCs) and CD8+ T cells in the ocular draining lymph nodes was significantly increased. These findings demonstrated that GM-gD-lip polarized CD169+ macrophages toward M1 to eliminate the virus while cross-presenting antigens to CD8+ T cells via DCs to activate adaptive immunity, ultimately attenuating the severity of HSK. The use of GM-gD-lip as an immunotherapeutic method for the treatment of HSK has significant implications.

Dysfunction of sinus macrophages in tumor-bearing host induces resistance to immunotherapy

Sinus macrophages in draining lymph nodes (DLNs) are involved in anti-tumor immune reactions. CD169 (Sialoadhesin, Siglec-1) is expressed on sinus macrophages and is considered a surrogate marker for the immunostimulatory phenotype of macrophages. In this study, the significance of sinus macrophages in immunotherapy was evaluated using mouse models. Treatment with anti-programmed death-ligand 1 (PD-L1) antibody suppressed the subcutaneous tumor growth of MC38 and E0771 cells but was not effective against MB49 and LLC tumors. Decreased cytotoxic T-lymphocyte (CTL) infiltration in tumor tissues and CD169 expression in sinus macrophages were observed in MB49 and LLC cells compared to corresponding parameters in MC38 and E0771 cells. The anti-tumor effects of the anti-PD-L1 antibody on MC38 and E0771 cells were abolished when sinus macrophages in DLNs were depleted, suggesting that sinus macrophages are involved in the therapeutic effect of the anti-PD-L1 antibody. Naringin activated sinus macrophages. Naringin inhibited tumor growth in MB49- and LLC-bearing mice but did not affect that in MC38- and E0771-bearing mice. The infiltration of CTLs in tumor tissues and their activation were increased by naringin, and this effect was impaired when sinus macrophages were depleted. Combination therapy with naringin and anti-PD-L1 antibody suppressed MB49 tumor growth. In conclusion, CD169-positive sinus macrophages in DLNs are critical for anti-tumor immune responses, and naringin suppresses tumor growth by activating CD169-positive sinus macrophages and anti-tumor CTL responses. The activation status of sinus macrophages has been suggested to differ among tumor models, and this should be investigated in future studies.

Persistence of circulating CD169+monocytes and HLA-DR downregulation underline the immune response impairment in PASC individuals: the potential contribution of different COVID-19 pandemic waves

The use of CD169 as a marker of viral infection has been widely discussed in the context of COVID-19, and in particular, its crucial role in the early detection of SARS-CoV-2 infection and its association with the severity and clinical outcome of COVID-19 were demonstrated. COVID-19 patients show relevant systemic alteration and immunological dysfunction that persists in individuals with post-acute sequelae of SARS-CoV-2 infection (PASC). It is critical to implement the characterization of the disease, focusing also on the possible impact of the different COVID-19 waves and the consequent effects found after infection. On this basis, we evaluated by flow cytometry the expression of CD169 and HLA-DR on monocytes from COVID-19 patients and PASC individuals to better elucidate their involvement in immunological dysfunction, also evaluating the possible impact of different pandemic waves. The results confirm CD169 RMFI is a good marker of viral infection. Moreover, COVID-19 patients and PASC individuals showed high percentage of CD169+ monocytes, but low percentage of HLA-DR+ monocytes and the alteration of systemic inflammatory indices. We have also observed alterations of CD169 and HLA-DR expression and indices of inflammation upon different COVID-19 waves. The persistence of specific myeloid subpopulations suggests a role of CD169+ monocytes and HLA-DR in COVID-19 disease and chronic post-infection inflammation, opening new opportunities to evaluate the impact of specific pandemic waves on the immune response impairment and systemic alterations with the perspective to provide new tools to monitoring new variants and diseases associated to emerging respiratory viruses.

Expression of macrophage/dendritic cell-related molecules in lymph node sinus macrophages

The role of sinus macrophages (SMs) in anticancer immune responses has received considerable interest in recent years, but the types of molecules that are expressed in human SMs have not yet been clarified in detail. We therefore sought to identify dendritic cell (DC)- or macrophage-related molecules in SMs in human lymph nodes (LNs). SMs are strongly positive for Iba-1, CD163, CD169, and CD209. CD169 (clone SP216) reacted with almost all SMs, mainly in the cell surface membrane, while CD169 (clone HSn 7D2) reacted with a subpopulation of SMs, mainly in the cytoplasm, with a significant increase observed after IFN-α stimulation. The immunoreactivity of clone HSn 7D2 was markedly reduced after transfection with small interfering RNA against CD169, while that of clone SP216 was slightly reduced. The induction of CCL8 and CXCL10 messenger RNA (mRNA) expression by IFN-α was confirmed using cultured macrophages and RT-qPCR, but fluorescence in situ hybridization did not detect CCL8 and CXCL10 mRNA expression in SMs. Single-cell RNA sequence data of LNs indicated that the highest level of CXCL10 gene expression occurred in monocytes. In conclusion, we found that CD209, also known as DC-related molecule, was expressed in human SMs. The heterogeneity observed in CD169 reacted with cone HSn 7D2 and SP216 was potentially due to the modification of CD169 protein by IFN stimulation. Further, no expression of CXCL10 mRNA in SMs suggested that SMs might be resident macrophages.

The interaction of placental micro-EVs with immune cells in vivo and in vitro

PROBLEM

Considerable evidence suggests that placental extracellular vesicles (EVs) interact with most types of leukocytes in vitro but in vivo biodistribution studies question whether these interactions are reflective of the situation in vivo.

METHOD OF STUDY

CellTracker Red CMTPX stained human placental micro-EVs were isolated from first trimester placental explant cultures. Equivalent amounts of micro-EVs were cultured with murine leukocytes in vitro or injected into pregnant or non-pregnant mice. After intravenous injection, on day 12.5 of gestation, major organs and blood samples were harvested 30 min or 24 h post injection.

RESULTS

We screened cryosections of the organs and confirmed that human placental EVs were specifically localised to the spleen, liver and the lungs 30 min or 24 h after injection. Immunohistochemistry showed that most of the EVs interacted with macrophages in those three organs and some of them also associated with T and B lymphocytes in the spleen or endothelial cells in the lungs and liver. Flow cytometry demonstrated that there was very little interaction between circulating leukocytes and EVs in vivo. While minimal, significantly more EVs interacted with leukocytes in pregnant than nonpregnant mice.

CONCLUSION

The major interaction between human placental micro-EVs and maternal leukocytes appear to be with macrophages predominantly in the splenic marginal zone, liver and lungs with little interaction between EVs and circulating leukocytes. Since marginal zone macrophages induce tolerance after phagocytosing apoptotic bodies it is likely that phagocytosis of placental EVs by marginal zone macrophages may also contribute to maternal immune tolerance.

Breast cancer associated CD169+ macrophages possess broad immunosuppressive functions but enhance antibody secretion by activated B cells

CD169⁺ resident macrophages in lymph nodes of breast cancer patients are for unknown reasons associated with a beneficial prognosis. This contrasts CD169⁺ macrophages present in primary breast tumors (CD169⁺ TAMs), that correlate with a worse prognosis. We recently showed that these CD169⁺ TAMs were associated with tertiary lymphoid structures (TLSs) and T_regs in breast cancer. Here, we show that CD169⁺ TAMs can be monocyte-derived and express a unique mediator profile characterized by type I IFNs, CXCL10, PGE₂ and inhibitory co-receptor expression pattern. The CD169⁺ monocyte-derived macrophages (CD169⁺ Mo-M) possessed an immunosuppressive function in vitro inhibiting NK, T and B cell proliferation, but enhanced antibody and IL6 secretion in activated B cells. Our findings indicate that CD169⁺ Mo-M in the primary breast tumor microenvironment are linked to both immunosuppression and TLS functions, with implications for future targeted Mo-M therapy.

Novel Histopathological Biomarkers in Prostate Cancer: Implications and Perspectives

Prostate cancer (PCa) is the second most frequently diagnosed cancer in men. Despite the significant progress in cancer diagnosis and treatment over the last few years, the approach to disease detection and therapy still does not include histopathological biomarkers. The dissemination of PCa is strictly related to the creation of a premetastatic niche, which can be detected by altered levels of specific biomarkers. To date, the risk factors for biochemical recurrence include lymph node status, prostate-specific antigen (PSA), PSA density (PSAD), body mass index (BMI), pathological Gleason score, seminal vesicle invasion, extraprostatic extension, and intraductal carcinoma. In the future, biomarkers might represent another prognostic factor, as discussed in many studies. In this review, we focus on histopathological biomarkers (particularly CD169 macrophages, neuropilin-1, cofilin-1, interleukin-17, signal transducer and activator of transcription protein 3 (STAT3), LIM domain kinase 1 (LIMK1), CD15, AMACR, prostate-specific membrane antigen (PSMA), Appl1, Sortilin, Syndecan-1, and p63) and their potential application in decision making regarding the prognosis and treatment of PCa patients. We refer to studies that found a correlation between the levels of biomarkers and tumor characteristics as well as clinical outcomes. We also hypothesize about the potential use of histopathological markers as a target for novel immunotherapeutic drugs or targeted radionuclide therapy, which may be used as adjuvant therapy in the future.

CD169 expression on monocytes as a marker for assessing type I interferon status in pediatric inflammatory diseases

BACKGROUND

Evaluation of type I interferons (IFNs) in inflammatory or autoimmune diseases is challenging because of their rapid clearance in peripheral blood. The IFN gene expression signature has recently been used to evaluate the IFN status; however, this is often a labor-intensive and time-consuming procedure. Therefore, we assessed the feasibility of measuring expression of an IFN-inducible protein, CD169 (Siglec-1), on monocytes and circulating levels of soluble CD169 as alternative markers for type I IFN status in various pediatric inflammatory diseases.

METHODS

Data from flow cytometric analysis of surface CD169 on monocytes and an enzyme-linked immunosorbent assay of soluble CD169 in peripheral blood were compared with serum IFN-α levels in 8 patients with viral infections, 5 with bacterial infections, 10 with systemic lupus erythematosus (SLE), 5 with Kikuchi-Fujimoto disease (KFD), 7 with Kawasaki disease (KD), and 8 with inflammatory bowel disease (IBD), and in 8 healthy controls.

RESULTS

Surface CD169 expression was detected mainly on CD14⁺ monocytes and was significantly increased in patients with viral infections, SLE, and KFD, but not in patients with bacterial infections, KD, and IBD. There were similar trends for circulating soluble CD169; however, there was a significant increase only in patients with viral infections. Surface CD169 levels were significantly correlated with serum levels of IFN-α and soluble CD169.

CONCLUSION

Analysis of CD169 expression on CD14⁺ monocytes may be useful for rapid assessment of type I IFN status for differentiation of pediatric inflammatory diseases from type 1 IFN-mediated diseases.

Elevated circulating monocytes and monocyte activation in COVID-19 convalescent individuals

Background

Monocytes and macrophages play a pivotal role in inflammation during acute SARS-CoV-2 infection. However, their contribution to the development of post-acute sequelae of SARS-CoV-2 infection (PASC) are not fully elucidated.

Methods

A cross-sectional study was conducted comparing plasma cytokine and monocyte levels among three groups: participants with pulmonary PASC (PPASC) with a reduced predicted diffusing capacity for carbon monoxide [DLCOc, <80%; (PG)]; fully recovered from SARS-CoV-2 with no residual symptoms (recovered group, RG); and negative for SARS-CoV-2 (negative group, NG). The expressions of cytokines were measured in plasma of study cohort by Luminex assay. The percentages and numbers of monocyte subsets (classical, intermediate, and non-classical monocytes) and monocyte activation (defined by CD169 expression) were analyzed using flow cytometry analysis of peripheral blood mononuclear cells.

Results

Plasma IL-1Ra levels were elevated but FGF levels were reduced in PG compared to NG. Circulating monocytes and three subsets were significantly higher in PG and RG compared to NG. PG and RG exhibited higher levels of CD169+ monocyte counts and higher CD169 expression was detected in intermediate and non-classical monocytes from RG and PG than that found in NG. Further correlation analysis with CD169+ monocyte subsets revealed that CD169+ intermediate monocytes negatively correlated with DLCOc%, and CD169+ non-classical monocytes positively correlated with IL-1α, IL-1β, MIP-1α, Eotaxin, and IFN-γ.

Conclusion

This study present evidence that COVID convalescents exhibit monocyte alteration beyond the acute COVID-19 infection period even in convalescents with no residual symptoms. Further, the results suggest that monocyte alteration and increased activated monocyte subsets may impact pulmonary function in COVID-19 convalescents. This observation will aid in understanding the immunopathologic feature of pulmonary PASC development, resolution, and subsequent therapeutic interventions.

CD169+ macrophage intrinsic IL-10 production regulates immune homeostasis during sepsis

Macrophages facilitate critical functions in regulating pathogen clearance and immune homeostasis in tissues. The remarkable functional diversity exhibited by macrophage subsets is dependent on tissue environment and the nature of the pathological insult. Our current knowledge of the mechanisms that regulate the multifaceted counter-inflammatory responses mediated by macrophages remains incomplete. Here, we report that CD169+ macrophage subsets are necessary for protection under excessive inflammatory conditions. We show that in the absence of these macrophages, even under mild septic conditions, mice fail to survive and exhibit increased production of inflammatory cytokines. Mechanistically, CD169+ macrophages control inflammatory responses via interleukin-10 (IL-10), as CD169+ macrophage-specific deletion of IL-10 was lethal during septic conditions, and recombinant IL-10 treatment reduced lipopolysaccharide (LPS)-induced lethality in mice lacking CD169+ macrophages. Collectively, our findings show a pivotal homeostatic role for CD169+ macrophages and suggest they may serve as an important target for therapy under damaging inflammatory conditions.

CD169+ sinus macrophages in regional lymph nodes do not predict mismatch-repair status of patients with colorectal cancer

AIMS

Mismatch-repair deficiency and microsatellite instability-high (dMMR/MSI-H) colorectal cancer (CRC) is treated with programmed death (PD)-1 antibody regardless of PD-ligand (L)1 expression in tumor cells. We previously found that abundant CD169⁺ macrophages in regional lymph node (RLN) sinuses and CD8⁺ tumor-infiltrating lymphocytes (TILs) positively correlated in CRC and were associated with a favorable prognosis. However, associations between dMMR/MSI-H CRC and CD8⁺ TILs or prognoses vary among studies. In this study, we attempted to compare the association between MMR status, CD169⁺ macrophages in RLNs, CD8⁺ TILs, PD-L1 scores, and prognoses in CRC.

METHODS AND RESULTS

We immunostained 83 surgically resected CRC tumors that we previously analyzed for MMR proteins, and identified 9 that were dMMR. The number of CD169⁺ macrophages in RLNs and CD8⁺ TILs significantly correlated with overall survival, whereas MMR status did not. The number of cells positive for the TIL markers CD3, CD4, CD8, and TIA-1, and macrophage markers CD68 and CD169 in RLNs did not significantly differ between groups according to MMR status. Furthermore, combined positive scores (CPS) for PD-L1 expression in five of nine dMMR CRCs were all <1. We found that dMMR in CRC did not correlate with numbers of CD169⁺ macrophages in RLNs or CD8⁺ TILs.

CONCLUSIONS

CRC with CD169⁺ macrophages in RLNs and abundant CD8⁺ TILs indicates a better prognosis and it should be immunologically classified as a different antitumor group from dMMR CRC.

CD169(+) Macrophages in Primary Breast Tumors Associate with Tertiary Lymphoid Structures, T(regs) and a Worse Prognosis for Patients with Advanced Breast Cancer

The presence of CD169⁺ macrophages in the draining lymph nodes of cancer patients is, for unknown reasons, associated with a beneficial prognosis. We here investigated the prognostic impact of tumor-infiltrating CD169⁺ macrophages in primary tumors (PTs) and their spatial relation to tumor-infiltrating B and T cells. Using two breast cancer patient cohorts, we show that CD169⁺ macrophages were spatially associated with the presence of B and T cell tertiary lymphoid-like structures (TLLSs) in both PTs and lymph node metastases (LNMs). While co-infiltration of CD169⁺/TLLS in PTs correlated with a worse prognosis, the opposite was found when present in LNMs. RNA sequencing of breast tumors further confirmed that SIGLEC1 (CD169) expression was associated with mature tertiary lymphoid structure (TLS), and T_reg and B_reg signatures. We propose that the negative prognostic value related to CD169⁺ macrophages in PTs is a consequence of an immunosuppressive tumor environment rich in TLSs, T_regs and B_regs.

Sialylation-dependent interaction between PD-L1 and CD169 promotes monocytes adhesion to endothelial cells

The monocyte adhesion to endothelial cells is an early step in chronic inflammation. Interferon-γ (IFN-γ) is regarded as a master regulator of inflammation development. However, the significance of IFN-γ in the monocyte adhesion to endothelial cells remains largely unknown. In this study, we found that IFN-γ increased PD-L1 transcription in endothelial cells through IRF-1 transcription factor, and subsequently enhanced the adhesion of monocyte to endothelial cells. PD-L1 in endothelial cells interacted with CD169/Siglec 1 in monocyte depending on the α2,3-sialylation of PD-L1. ST3Gal4 (ST3β-galactoside α-2,3-sialyltransferase 4) was the major glycosyltransferase responsible for the α2,3-sialylation of PD-L1. Down-regulation of α2,3-sialylation of PD-L1 by ST3Gal4 knockdown reduced the PD-L1-CD169 interaction. Purified PD-L1 protein with α2,3-sialylation, but not PD-L1 protein without α2,3-sialylation, reduced IFN-γ-induced monocytes adhesion to endothelial cells. Collectively, the interaction between PD-L1 and CD169 promoted monocytes adhesion to endothelial cells. Our findings provide a new mechanism of monocytes adhesion to endothelial cells.

CD169+ Macrophages Residing in the Draining Lymph Nodes and Infiltrating the Tumor Play Opposite Roles in the Pathogenesis of Bladder Cancer

Purpose

CD169⁺ macrophages are considered to enhance anti-tumor immunity by capturing lymph-borne dead tumor cells. The number of CD169⁺ macrophages in regional lymph nodes (RLNs) is positively correlated with prolonged cancer-free survival in various human cancers. However, a recent study argued against this dogma; that is, CD169⁺ macrophages infiltrating into the tumor were associated with poor prognosis in patients with breast cancer. To explain this discrepancy, we quantified the number of CD169⁺ macrophages located in the bladder tumor and RLNs of the same patients and examined their relationship with the 5-year survival rate.

Patients and Methods

Tumor and RLN specimens resected from 40 invasive bladder cancer patients (29 males and 11 females; median age, 70.7 years; range, 49-81 years) who underwent radical cystectomy were evaluated using immunostaining.

Results

The number of CD169⁺ macrophages in RLNs was associated with a good cancer prognosis, while CD169⁺ macrophages infiltrating the tumor strongly correlated with a higher incidence of lymphovascular invasion.

Conclusion

CD169⁺ macrophages play opposing roles in the induction of anti-tumor immunity based on their location in RLNs or tumors.

Nonclinical pharmacokinetics and biodistribution of VSV-GP using methods to decouple input drug disposition and viral replication

Viral replication places oncolytic viruses (OVs) in a unique niche in the field of drug pharmacokinetics (PK) as their self-amplification obscures exposure-response relationships. Moreover, standard bioanalytical techniques are unable to distinguish the input from replicated drug products. Here, we combine two novel approaches to characterize PK and biodistribution (BD) after systemic administration of vesicular stomatitis virus pseudotyped with lymphocytic choriomeningitis virus glycoprotein (VSV-GP) in healthy mice. First: to decouple input drug PK/BD versus replication PK/BD, we developed and fully characterized a replication-incompetent tool virus that retained all other critical attributes of the drug. We used this approach to quantify replication in blood and tissues and to determine its impact on PK and BD. Second: to discriminate the genomic and antigenomic viral RNA strands contributing to replication dynamics in tissues, we developed an in situ hybridization method using strand-specific probes and assessed their spatiotemporal distribution in tissues. This latter approach demonstrated that distribution, transcription, and replication localized to tissue-resident macrophages, indicating their role in PK and BD. Ultimately, our study results in a refined PK/BD profile for a replicating OV, new proposed PK parameters, and deeper understanding of OV PK/BD using unique approaches that could be applied to other replicating vectors.

A rapid, easy, and scalable whole blood monocyte CD169 assay for outpatient screening during SARS-CoV-2 outbreak, and potentially other emerging disease outbreaks

Objective:

The COVID-19 corona virus disease outbreak is globally challenging health systems and societies. Its diagnosis relies on molecular methods, with drawbacks revealed by mass screening. Upregulation of neutrophil CD64 or monocyte CD169 has been abundantly reported as markers of bacterial or acute viral infection, respectively. We evaluated the sensitivity of an easy, one-step whole blood flow cytometry assay to measure these markers within 10 min, as a potential screening test for COVID-19 patients.

Methods:

Patients (n = 177) with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were tested on 10 µL blood and results were compared with reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR).

Results:

We observed 98% and 100% sensitivity in early-stage (n = 52) and asymptomatic patients (n = 9), respectively. Late-stage patients, who presented for a second control RT-qPCR, were negative for both assays in most cases. Conversely, neutrophil CD64 expression was unchanged in 75% of cases, without significant differences between groups.

Conclusion:

Monocyte CD169 evaluation was highly sensitive for detecting SARS-CoV-2 infection in first-presentation patients; and it returns to basal level upon infection clearance. The potential ease of fingerprick collection, minimal time-to-result, and low cost rank this biomarker measurement as a potential viral disease screening tool, including COVID-19. When the virus prevalence in the tested population is usually low (1%−10%), such an approach could increase the testing capacity 10 to 100-fold, with the same limited molecular testing resources, which could focus on confirmation purposes only.

A Microbiota-Dependent Subset of Skin Macrophages Protects Against Cutaneous Bacterial Infection

Microbiota is essential to the development and functional maturation of the immune system. The effects of the gut microbiota on myeloid cells remote from the gut, especially the skin remain unclear. Transcriptomic analysis revealed that type I interferon (IFN) signaling was down-regulated in the skin of germ-free mice compared to that in specific pathogen-free mice. The decrease in type I IFN signaling was closely related to the presence of microbiota and macrophage-specific marker CD169. The absence of CD169⁺ macrophages resulted in increased bacterial burden and impaired immune responses against Staphylococcus aureus skin infection. CD169⁺ macrophages mediated the recruitment of γδ T cells as well as the activation of γδ T cells via interleukin (IL)-23. Our findings demonstrate the role of the microbiota in establishment of a specific myeloid cell subset expressing CD169 in the skin and provide evidence of a specific mechanism by which this subset protects against bacterial skin infection.

Type I IFNs repolarized a CD169+ macrophage population with anti-tumor potentials in hepatocellular carcinoma

Macrophages constitute a major component in human hepatocellular carcinoma (HCC) and perform various functions to facilitate disease progression. Reprogramming or reconstituting the tumor surveillance phenotypes of macrophages represents an attractive immunotherapeutic strategy in cancer treatments. The current study identified CD169 as a potential target for macrophage repolarization since it signified a population of macrophages positively correlated with an activated immune signature and better prognosis of patients with HCC. In vitro experiments revealed that a low dose of type I interferon (IFN) could effectively reprogram human monocyte-derived macrophages to upregulate CD169 expression, and such induced CD169⁺ macrophages exhibited significantly enhanced phagocytotic and CD8⁺ T cell-activating capacities compared to controls. A low dose of IFNα also inhibited hepatoma growth in mice in vivo, presumably through polarizing the CD169⁺ macrophage population and enhancing CD8⁺ T cell activities. Notably, IFNα also induced substantial PD-L1 expression on macrophages in vivo, and thus blockade of PD-L1 could further increase the anti-tumor efficacy of IFNα in the treatment of HCC. We propose a low dose of IFNα in combination with a PD-L1 blocking agent as a potential anti-tumor therapeutic strategy via its effects on macrophage polarization.

High CD169 Monocyte/Lymphocyte Ratio Reflects Immunophenotype Disruption and Oxygen Need in COVID-19 Patients

BACKGROUND

Sialoadhesin (CD169) has been found to be overexpressed in the blood of COVID-19 patients and identified as a biomarker in early disease. We analyzed CD169 in the blood cells of COVID-19 patients to assess its role as a predictive marker of disease progression and clinical outcomes.

METHODS

The ratio of the median fluorescence intensity of CD169 between monocytes and lymphocytes (CD169 RMFI) was analyzed by flow cytometry in blood samples of COVID-19 patients (COV) and healthy donors (HDs) and correlated with immunophenotyping, inflammatory markers, cytokine mRNA expression, pulmonary involvement, and disease progression.

RESULTS

CD169 RMFI was high in COV but not in HDs, and it correlated with CD8 T-cell senescence and exhaustion markers, as well as with B-cell maturation and differentiation in COV. CD169 RMFI correlated with blood cytokine mRNA levels, inflammatory markers, and pneumonia severity in patients who were untreated at sampling, and was associated with the respiratory outcome throughout hospitalization. Finally, we also report the first evidence of the specific ability of the spike protein of SARS-CoV-2 to trigger CD169 RMFI in a dose-dependent manner in parallel with IL-6 and IL-10 gene transcription in HD PBMCs stimulated in vitro.

CONCLUSION

CD169 is induced by the spike protein and should be considered as an early biomarker for evaluating immune dysfunction and respiratory outcomes in COVID-19 patients.

Evaluation of SIGLEC1 in the diagnosis of suspected systemic lupus erythematosus

OBJECTIVES

To evaluate and compare the diagnostic accuracy of SIGLEC1, a surrogate marker of type I IFN, with established biomarkers in an inception cohort of systemic lupus erythematosus (SLE).

METHODS

SIGLEC1 was analyzed by flow cytometry in 232 patients referred to our institution with suspected SLE between October 2015 and September 2020.

RESULTS

SLE was confirmed in 76 of 232 patients (32.8%) according to the 2019 EULAR/ACR classification criteria and their SIGLEC1 values were significantly higher compared with patients without SLE (p< 0.0001). A sensitivity of 98.7%, a specificity of 82.1%, a negative predictive value (NPV) of 99.2% and a positive predictive value (PPV) of 72.8% were calculated for SIGLEC1. Adjusted to the highest reported prevalence of SLE, the NPV and PPV were > 99.9% and 0.1%, respectively. Using ROC analysis and Delong testing, the area under the curve (AUC) for SIGLEC1 (AUC = 0.95) was significantly higher than for ANA (AUC = 0.88, p= 0.031), C3 (AUC = 0.83, p= 0.001) and C4 (AUC = 0.83, p= 0.002) but not for anti-dsDNA antibodies (AUC = 0.90, p= 0.163).

CONCLUSION

IFN-I pathway activation is detectable in almost all newly diagnosed SLE patients. Thus, a negative test result for SIGLEC1 is powerful to exclude SLE in suspected cases.

A Myeloid Signature-Based Nomogram Predicts the Postoperative Recurrence of Intrahepatic Cholangiocarcinoma

Intrahepatic cholangiocarcinoma (iCCA) is the second most common cancer in liver, with a high recurrence rate after surgery. Recently, we identified a CD11b-CD169-based myeloid response score (MRS), which showed remarkable prognostic potential in hepatocellular carcinoma (HCC). Here, we aimed to verify the prognostic value of the MRS in iCCA and establish an MRS-based nomogram to predict the postoperative prognosis of iCCA patients. From April 2005 to March 2017, a total of 84 patients from the Third Affiliated Hospital of Sun Yat-sen University were enrolled. Preoperative clinical information and surgical specimens of enrolled patients were collected. Among these, tissues from 75 patients passed the clinical data quality control and the staining quality control. The protein expression of CD11b and CD169 in iCCA samples were detected by immunohistochemistry (IHC). Kaplan-Meier analysis and receiver operating characteristic (ROC) curves revealed that the MRS had a high discriminatory ability for predicting the time to recurrence (TTR) of iCCA patients after surgery. Three independent risk factors selected by a Cox proportional hazards regression analysis, namely, the MRS, the tumor size and the status of vascular invasion, were included to construct a nomogram to predict the recurrence of iCCA after resection surgery. ROC curves, calibration analysis and decision curve analysis (DCA) suggested that this nomogram had notable discriminatory power, stability and clinical usefulness in predicting the postoperative recurrence. Together, we explored the prognostic value of the MRS in iCCA, and constructed an MRS-based nomogram which may help to predict postoperative recurrence and aid clinical decisions for iCCA patients.

Prognostic value of CD169-positive macrophages in various tumors: a meta-analysis

The study aimed to evaluate the prognostic value of CD169 expression in tumor-infiltrating macrophages from regional lymph nodes (RLN) in various tumors. In order to identify eligible articles, PubMed, EMBASE, Web of Science, and Cochrane Library were used to conduct a systematic search. Pooled hazard ratios (HRs) or odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were adopted to assess the relationship between CD169 expression and overall survival (OS) and clinicopathological characteristics. Ten studies, including eleven cohorts with 1699 patients, were enrolled. We found that high CD169⁺ expression in tumor-infiltrating macrophages from RLN was associated with a favorable OS (HR = 0.56, 95%CI: 0.39–0.79, P = 0.001). Subgroup analysis showed that high CD169+ expression had more predictive power in digestive system tumors (HR = 0.52, 95%CI: 0.42–0.67, <0.001). In addition, high CD169 expression was significantly linked with lymph node metastasis (OR = 0.66, 95%CI: 0.47–0.94, P = 0.020) and TNM stage (OR = 0.62, 95%CI: 0.48–0.80, P < 0.001). High CD169 expression in tumor-infiltrating macrophages from RLN was correlated with favorable survival outcome in patients with malignancies. CD169 may be a novel and effective prognostic marker, especially for digestive system tumors.

Direct freezing of whole blood enables analysis of leucocyte markers by flow cytometry: a proof-of-concept study

Aim: A new one-step flow cytometry procedure has been recently demonstrated for identifying subjects with infections, but only for fresh whole blood samples. The goal of this study was to assess its applicability on frozen samples, by proposing a new method to perform the sample freezing directly and easily. Methods: Fresh blood was tested, then frozen either directly or with dimethylsulfoxide and serum. Common markers of white blood cells as well as infection-related biomarkers were tested. Results: All percentages of leucocyte subsets and levels of infection-related biomarkers were significantly correlated between frozen and fresh samples. Conclusion: The direct freezing method enables an accurate assessment of common cellular sub-populations and of levels of important infectious biomarkers via flow cytometry.

Research progress on CD169-positive macrophages in tumors

CD169/Siglec1/sialoadhesin, a sialic acid-binding immunoglobulin-like lectin, is mainly expressed in metallophilic macrophages in the marginal zone of the spleen and in macrophages in the subcapsular sinus and medulla of lymph nodes. In addition to participating in anti-infectious immunity, recent studies have demonstrated that CD169⁺ macrophages are involved in tumor immunity and are associated with a favorable prognosis. The roles of CD169⁺ macrophages in tumors and the mechanisms of CD169⁺ macrophages and CD169 molecules involved in the tumor microenvironment and tumor immunity are described in this review.

CD169 Defines Activated CD14+ Monocytes With Enhanced CD8+ T Cell Activation Capacity

Monocytes are antigen-presenting cells (APCs) that play diverse roles in promoting or regulating inflammatory responses, but their role in T cell stimulation is not well defined. In inflammatory conditions, monocytes frequently show increased expression of CD169/Siglec-1, a type-I interferon (IFN-I)-regulated protein. However, little is known about the phenotype and function of these CD169⁺ monocytes. Here, we have investigated the phenotype of human CD169⁺ monocytes in different diseases, their capacity to activate CD8⁺ T cells, and the potential for a targeted-vaccination approach. Using spectral flow cytometry, we detected CD169 expression by CD14⁺ CD16^- classical and CD14⁺ CD16⁺ intermediate monocytes and unbiased analysis showed that they were distinct from dendritic cells, including the recently described CD14-expressing DC3. CD169⁺ monocytes expressed higher levels of co-stimulatory and HLA molecules, suggesting an increased activation state. IFNα treatment highly upregulated CD169 expression on CD14⁺ monocytes and boosted their capacity to cross-present antigen to CD8⁺ T cells. Furthermore, we observed CD169⁺ monocytes in virally-infected patients, including in the blood and bronchoalveolar lavage fluid of COVID-19 patients, as well as in the blood of patients with different types of cancers. Finally, we evaluated two CD169-targeting nanovaccine platforms, antibody-based and liposome-based, and we showed that CD169⁺ monocytes efficiently presented tumor-associated peptides gp100 and WT1 to antigen-specific CD8⁺ T cells. In conclusion, our data indicate that CD169⁺ monocytes are activated monocytes with enhanced CD8⁺ T cell stimulatory capacity and that they emerge as an interesting target in nanovaccine strategies, because of their presence in health and different diseases.

CD169/SIGLEC1 is expressed on circulating monocytes in COVID-19 and expression levels are associated with disease severity

Coronavirus disease 2019 (COVID-19) is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Type I interferons are important in the defense of viral infections. Recently, neutralizing IgG auto-antibodies against type I interferons were found in patients with severe COVID-19 infection. Here, we analyzed expression of CD169/SIGLEC1, a well described downstream molecule in interferon signaling, and found increased monocytic CD169/SIGLEC1 expression levels in patients with mild, acute COVID-19, compared to patients with severe disease. We recommend further clinical studies to evaluate the value of CD169/SIGLEC1 expression in patients with COVID-19 with or without auto-antibodies against type I interferons.

New Tools for Early Diagnosis in COVID-19 Pandemic

Objectives: Several parameters aid in deciphering between viral and bacterial infections; however, new tools should be investigated in order to reduce the time to results and proceed with an early target-therapy. Validation of a biomarker study, including CD64 and CD169 expression, was conducted.

Material and Methods: Patients with active SARS-CoV-2 infection (ACov-2), bacterial infection (ABI), healthy controls, and antiretroviral-controlled chronic HIV infection were assessed. Whole blood was stained and, after lysing no-wash protocol, acquired by flow cytometry. The median fluorescence intensity (MFI) of CD64 and CD169 was measured in granulocytes, monocytes, and lymphocytes. The CD64 MFI ratio granulocytes to lymphocytes (CD64N) and CD169 MFI ratio monocytes to lymphocytes (CD169Mo) were evaluated as biomarkers of acute bacterial and viral infection, respectively.

Results: A CD64N ratio higher than 3.3 identified patients with ABI with 83.3 and 85.9% sensitivity and specificity, with an area under the curve (AUC) of 83.5%. In contrast, other analytic or hematological parameters used in the clinic had lower AUC compared with the CD64N ratio. Moreover, a CD169Mo ratio higher than 3.3 was able to identify ACov-2 with 91.7 and 89.8 sensitivity and specificity, with the highest AUC (92.0%).

Conclusion: This work confirms the previous data of CD64N and CD169Mo ratios in an independent cohort, including controlled chronic viral HIV infection patients as biomarkers of acute bacterial and viral infections, respectively. Such an approach would benefit from quick pathogen identification for a direct-therapy with a clear application in different Health Care Units, especially during this COVID pandemic.

CD169 Expression on Lymph Node Macrophages Predicts in Patients With Gastric Cancer

The induction of an anti-cancer immune responses is potentially associated with the efficacy of anti-cancer therapy. Recent studies have indicated that sinus macrophages in regional lymph nodes are involved in anti-cancer immune responses in the cancer microenvironment. In the present study, we investigated the correlation between lymphocyte infiltration in cancer tissues and macrophage activation in regional lymph nodes. We retrospectively identified 294 patients with gastric cancer who underwent surgery from 2008 to 2012. Using immunohistochemistry, we evaluated CD169-expression on CD68-positive macrophages, and the density of CD8-postive lymphocytes in tumor microenvironment. We statistically examined the correlation between CD169 and CD8 expression, and performed Cox regression analysis of potential prognostic factors, including CD169 and CD8 expression, for cancer-specific survival (CSS) in patients with total and advanced gastric cancer. CD169 overexpression in lymph node sinus macrophages (LySMs) was positively correlated to the density of CD8-positive lymphocytes in primary cancer tissues (R = 0.367, p < 0.001). A high density of CD8-positive T lymphocytes in the primary site and a high level of CD169 expression in LySMs were independently associated with greater CSS in patients with total and advanced gastric cancer (p < 0.05 for all). The expression on CD169 in LySMs is a predictor of a favorable clinical course in patients with gastric cancer, and might be useful for evaluating anti-cancer immune responses.

Monocyte CD169 Expression as a Biomarker in the Early Diagnosis of Coronavirus Disease 2019

We assessed the expression of CD169, a type I interferon-inducible receptor, on monocytes (mCD169) in 53 adult patients admitted to the hospital during the COVID-19 outbreak for a suspicion of SARS-CoV-2 infection. mCD169 was strongly overexpressed in 30 out of 32 (93.7%) confirmed COVID-19 cases, compared to three out of 21 (14.3%) patients in whom the diagnosis of COVID-19 was finally ruled out. mCD169 was associated with the plasma interferon alpha level and thrombocytopenia. mCD169 testing may be helpful for the rapid triage of suspected COVID-19 patients during an outbreak.

Monocyte CD169 expression in COVID-19 patients upon intensive care unit admission

During the second surge of COVID‐19 in France (fall 2020), we assessed the expression of monocyte CD169 (i.e., Siglec‐1, one of the numerous IFN‐stimulated genes) upon admission to intensive care units of 45 patients with RT‐PCR‐confirmed SARS‐CoV2 pulmonary infection. Overall, CD169 expression was strongly induced on circulating monocytes of COVID‐19 patients compared with healthy donors and patients with bacterial sepsis. Beyond its contribution at the emergency department, CD169 testing may be also helpful for patients' triage at the ICU to rapidly reinforce suspicion of COVID‐19 etiology in patients with acute respiratory failure awaiting for PCR results for definitive diagnosis.

Liposome induction of CD8+ T cell responses depends on CD169+ macrophages and Batf3-dependent dendritic cells and is enhanced by GM3 inclusion

Cancer vaccines aim to efficiently prime cytotoxic CD8⁺ T cell responses which can be achieved by vaccine targeting to dendritic cells. CD169⁺ macrophages have been shown to transfer antigen to dendritic cells and could act as an alternative target for cancer vaccines. Here, we evaluated liposomes containing the CD169/Siglec-1 binding ligand, ganglioside GM3, and the non-binding ligand, ganglioside GM1, for their capacity to target antigens to CD169⁺ macrophages and to induce immune responses. CD169⁺ macrophages demonstrated specific uptake of GM3 liposomes in vitro and in vivo that was dependent on a functional CD169 receptor. Robust antigen-specific CD8⁺ and CD4⁺ T and B cell responses were observed upon intravenous administration of GM3 liposomes containing the model antigen ovalbumin in the presence of adjuvant. Immunization of B16-OVA tumor bearing mice with all liposomes resulted in delayed tumor growth and improved survival. The absence of CD169⁺ macrophages, functional CD169 molecules, and cross-presenting Batf3-dependent dendritic cells (cDC1s) significantly impaired CD8⁺ T cell responses, while B cell responses were less affected. In conclusion, we demonstrate that inclusion of GM3 in liposomes enhance immune responses and that splenic CD169⁺ macrophages and cDC1s are required for induction of CD8⁺ T cell immunity after liposomal vaccination.

A distinct innate immune signature marks progression from mild to severe COVID-19

Coronavirus disease 2019 (COVID-19) manifests with a range of severities, but immune signatures of mild and severe disease are still not fully understood. Here, we use mass cytometry and targeted proteomics to profile the innate immune response of patients with mild or severe COVID-19 and of healthy individuals. Sampling at different stages allows us to reconstruct a pseudo-temporal trajectory of the innate response. A surge of CD169+ monocytes associated with an IFN-γ+MCP-2+ signature rapidly follows symptom onset. At later stages, we observe a persistent inflammatory phenotype in patients with severe disease, dominated by high CCL3 and CCL4 abundance correlating with the re-appearance of CD16+ monocytes, whereas the response of mild COVID-19 patients normalizes. Our data provide insights into the dynamic nature of inflammatory responses in COVID-19 patients and identify sustained innate immune responses as a likely mechanism in severe patients, thus supporting the investigation of targeted interventions in severe COVID-19.

Development of Sentinel LN Imaging with a Combination of HAase Based on a Comprehensive Analysis of the Intra-lymphatic Kinetics of LPs

The sentinel lymph node (LN) is the first LN to which lymph fluid flows from tumor tissue. We identified the key parameters of liposomes (LPs) that affect their accumulation in regional (primary) LNs with minimum leakage to its connecting (secondary) LNs by a comprehensive analysis of the LN-to-LN trafficking of LPs with various surface charges and various sizes. We used a lymphatic flow-modified (LFM) mouse that allows for the chronological analysis of inguinal (primary) LN-to-axillary (secondary) LN at the body surface. As a result, the anionic medium-sized LPs (130 nm on average) exhibited the highest accumulation in the primary LNs. A mechanism-based analysis revealed that CD169-positive macrophages in LNs were the dominant cell population that captures anionic LPs. Sentinel LN imaging was also performed by the intratumoral injection of fluorescent medium-sized anionic LPs using a breast cancer orthotopic model. In comparison with the typically used contrast agent indocyanine green, the anionic LPs were detected in sentinel LNs with a high sensitivity. Additionally, the co-injection of hyaluronidase significantly improved the sensitivity of detection of the fluorescent LPs in sentinel LNs. In conclusion, medium-sized anionic LPs combined with hyaluronidase represents a potent strategy for investigating sentinel LNs.

Optimization of Liposomes for Antigen Targeting to Splenic CD169+ Macrophages

Despite promising progress in cancer vaccination, therapeutic effectiveness is often insufficient. Cancer vaccine effectiveness could be enhanced by targeting vaccine antigens to antigen-presenting cells, thereby increasing T-cell activation. CD169-expressing splenic macrophages efficiently capture particulate antigens from the blood and transfer these antigens to dendritic cells for the activation of CD8⁺ T cells. In this study, we incorporated a physiological ligand for CD169, the ganglioside GM3, into liposomes to enhance liposome uptake by CD169⁺ macrophages. We assessed how variation in the amount of GM3, surface-attached PEG and liposomal size affected the binding to, and uptake by, CD169⁺ macrophages in vitro and in vivo. As a proof of concept, we prepared GM3-targeted liposomes containing a long synthetic ovalbumin peptide and tested the capacity of these liposomes to induce CD8⁺ and CD4⁺ T-cell responses compared to control liposomes or soluble peptide. The data indicate that the delivery of liposomes to splenic CD169⁺ macrophages can be optimized by the selection of liposomal constituents and liposomal size. Moreover, optimized GM3-mediated liposomal targeting to CD169⁺ macrophages induces potent immune responses and therefore presents as an interesting delivery strategy for cancer vaccination.

Co-localization of CD169+ macrophages and cancer cells in lymph node metastases of breast cancer patients is linked to improved prognosis and PDL1 expression

Breast cancer is the most common form of cancer in women worldwide. Although the survival among breast cancer patients has improved, there is still a large group of patients with dismal prognosis. One of the most important prognostic factors for poor prognosis is lymph node metastasis. Increasing knowledge concerning the lymph nodes of breast cancer patients indicates that they are affected by the primary tumor. In this study we show that presence of CD169⁺ subcapsular sinus macrophages in contact with lymph node metastases in breast cancer patients, is related to better prognosis after adjuvant tamoxifen treatment, but only in patients with PDL1⁺ primary tumors. This is in contrast to the prognostic effect of CD169⁺ primary tumor-associated macrophages (TAMs). We further show that CD169⁺ macrophages were spatially associated with expression of PDL1 on nearby cells, both in primary tumors and metastatic lymph node, although PDL1 expression in metastatic lymph node as such did not have further prognostic impact. Our data suggest that CD169⁺ resident lymph node macrophages have a unique function in targeting immune responses against breast cancer and should be further investigated in detail.

Susceptibility of immortalized porcine kidney macrophages to porcine reproductive and respiratory syndrome virus-2 infection

Porcine reproductive and respiratory syndrome virus (PRRSV) displays restricted tropism to porcine alveolar macrophages in nature. Meanwhile, non-porcine cell lines derived from African green monkey kidney cell lines are permissive to PRRSV, resulting in their widespread use in PRRSV research. Furthermore, genetically modified cell lines expressing receptors targeted by PRRSV have been established. We previously established porcine immortalized kidney-derived macrophages (IPKMs) that maintained typical macrophage function. In the present study, we demonstrated the advantages of IPKMs for PRRSV research. IPKMs expressed receptors for PRRSV such as CD163 and CD169. The efficiency of virus isolation from field biological samples was higher for IPKMs than for MARC-145 cells. Five different clusters of North American type PRRSV were propagated in IPKMs. Four field strains continuously produced progeny viruses during 10 continuous passages. The efficiency of virus isolation from field biological samples and continuous progeny virus production in the sequential passages using IPKMs indicated that these cells are good vessels for PRRSV research.

Selective tumor antigen vaccine delivery to human CD169+ antigen-presenting cells using ganglioside-liposomes

Priming of CD8+ T cells by dendritic cells (DCs) is crucial for the generation of effective antitumor immune responses. Here, we describe a liposomal vaccine carrier that delivers tumor antigens to human CD169/Siglec-1+ antigen-presenting cells using gangliosides as targeting ligands. Ganglioside-liposomes specifically bound to CD169 and were internalized by in vitro-generated monocyte-derived DCs (moDCs) and macrophages and by ex vivo-isolated splenic macrophages in a CD169-dependent manner. In blood, high-dimensional reduction analysis revealed that ganglioside-liposomes specifically targeted CD14+ CD169+ monocytes and Axl+ CD169+ DCs. Liposomal codelivery of tumor antigen and Toll-like receptor ligand to CD169+ moDCs and Axl+ CD169+ DCs led to cytokine production and robust cross-presentation and activation of tumor antigen-specific CD8+ T cells. Finally, Axl+ CD169+ DCs were present in cancer patients and efficiently captured ganglioside-liposomes. Our findings demonstrate a nanovaccine platform targeting CD169+ DCs to drive antitumor T cell responses.

Interferon Alpha Favors Macrophage Infection by Visceral Leishmania Species Through Upregulation of Sialoadhesin Expression

Type I interferons (IFNs) induced by an endogenous Leishmania RNA virus or exogenous viral infections have been shown to exacerbate infections with New World Cutaneous Leishmania parasites, however, the impact of type I IFNs in visceral Leishmania infections and implicated mechanisms remain to be unraveled. This study assessed the impact of type I IFN on macrophage infection with L. infantum and L. donovani and the implication of sialoadhesin (Siglec-1/CD169, Sn) as an IFN-inducible surface receptor. Stimulation of bone marrow-derived macrophages with type I IFN (IFN-α) significantly enhanced susceptibility to infection of reference laboratory strains and a set of recent clinical isolates. IFN-α particularly enhanced promastigote uptake. Enhanced macrophage susceptibility was linked to upregulated Sn surface expression as a major contributing factor to the infection exacerbating effect of IFN-α. Stimulation experiments in Sn-deficient macrophages, macrophage pretreatment with a monoclonal anti-Sn antibody or a novel bivalent anti-Sn nanobody and blocking of parasites with soluble Sn restored normal susceptibility levels. Infection of Sn-deficient mice with bioluminescent L. infantum promastigotes revealed a moderate, strain-dependent role for Sn during visceral infection under the used experimental conditions. These data indicate that IFN-responsive Sn expression can enhance the susceptibility of macrophages to infection with visceral Leishmania promastigotes and that targeting of Sn may have some protective effects in early infection.

Role of the interferons in CD64 and CD169 expressions in whole blood: Relevance in the balance between viral- or bacterial-oriented immune responses

Introduction

CD64 expression increases on neutrophils during bacterial infections. Recently an increase in CD169 expression has been discovered on monocytes during viral infections. Generally, interferons α (IFNsα) and IFNsγ are key drivers of the infectious host immune response. The purpose of this study was to explore if a link exists between these IFNs and both biomarkers.

Methods

Whole blood samples from healthy volunteers were stimulated with either IFNs, interleukins, or infectious extracts, to mimic an infectious state. Expressions of CD64 and CD169 were assessed in these samples by multiple flow cytometry methods, over precise kinetics.

Results

The expression of CD64 was statistically higher in samples stimulated with IFNγ, and CD169 in those stimulated with IFNα (and all other type I IFNs). Surface expressions are directly induced by their respective IFNs via Janus kinase/signal transducer and activator of transduction pathways within 6 to 8 hours of incubation. Mixing both types of IFNs seemed to indicate that they partially inhibit each other.

Conclusions

The induction of CD169 on monocytes and CD164 on neutrophils by type I and type II IFNs confirms the relevance of these markers for assessing between a viral‐ vs bacterial‐oriented immune response.

Macrophage Depletion Mitigates Platelet Aggregate Formation in Splenic Marginal Zone and Alleviates LPS-Associated Thrombocytopenia in Rats

Sepsis is often accompanied with thrombocytopenia partly due to platelet sequestration in the lung and liver. The spleen can store up to one-third of circulating platelets and can also significantly affect platelet transfusion outcomes by accumulating platelets. However, in sepsis, it is not clear whether there are platelet changes in the spleen which could contribute to sepsis-associated thrombocytopenia and also influence platelet transfusion outcomes. By using confocal microscopy, we examined endogenous rat platelets and infused human platelets in the spleen of severe combined immune deficient Rag2 KO rats which were injected intraperitoneally with lipopolysaccharide (LPS). LPS-injected Rag2 KO rats developed sepsis as indicated by increased TNFa, IL-6, IL-1b, and IL-10 levels and thrombocytopenia. Large platelet aggregates were observed in the spleen with majority located in the marginal zone and closely associated with CD169+ macrophages. Depletion of macrophages by clodrosome resulted in reduction of LPS-induced cytokine generation and alleviated LPS-induced thrombocytopenia. Macrophage depletion also remarkedly diminished large platelet aggregate formation in the splenic marginal zone but had less effect on those in red pulp. Infusion of human platelets into LPS-injected rats failed to raise platelet counts in the peripheral blood. In LPS-injected rat spleen, human platelets interacted with aggregated rat platelets in the marginal zone. In contrast, human platelets infused into control rats were located outside of splenic marginal zone. This study provides morphological evidence of platelet aggregates in the splenic marginal zone in sepsis which can interact with infused platelets and thus can contribute to platelet infusion refractoriness in sepsis. It indicates that macrophages play an important role in LPS-associated thrombocytopenia. It also suggests that CD169+ macrophages support platelet aggregate formation in the splenic marginal zone.

Activation of sialoadhesin down-regulates the levels of innate antiviral cytokines in porcine alveolar macrophages in vitro

Porcine sialoadhesin (pSn) is a crucial porcine reproductive and respiratory syndrome virus (PRRSV) receptor mediating the attachment and internalization of virus into its major target cells, porcine alveolar macrophages (PAMs). However, the role of pSn in innate antiviral immune response has not yet been investigated. In this study, our results showed that PRRSV down-regulated significantly the mRNA levels of IFN-α, IFN-β, IFN-γ, IFN-λ1, IFN-λ3 and IFN-λ4 and up-regulated significantly the mRNA levels of IL-10 and pSn in infected PAMs in vitro, suggesting that PRRSV infection inhibited the transcription of innate antiviral cytokines in host cells. Our results also showed that selective activation of pSn down-regulated significantly the mRNA levels of IFN-α, IFN-β, IFN-γ, IFN-λ1, IFN-λ3, IFN-λ4 and TNF-α and up-regulated significantly the mRNA level of IL-10 in PAMs in vitro, suggesting that pSn signaling inhibited the transcription of innate antiviral cytokines. Further results showed that pSn1, pSn2, pSn3, pSn4 and pSn5 domains of pSn were responsible for the inhibition of levels of innate antiviral cytokines. In conclusion, our results suggested that pSn suppressed innate antiviral immune response by down-regulating the levels of innate antiviral cytokines in PAMs. It was possible that PRRSV-pSn interaction may suppress innate antiviral immune response to PRRSV infection by repressing the production of innate antiviral cytokines.

Clinical research assessment by flow cytometry of biomarkers for infectious stratification in an Emergency Department

Aim: Management of patients with infections within the Emergency Department (ED) is challenging for practitioners, as the identification of infectious causes remains difficult with current techniques. A new combination of two biomarkers was tested with a new rapid flow cytometry technique. Materials & methods: Subjects from the ED were tested for their CD64 on neutrophils (nCD64) and CD169 on monocytes (mCD169) levels and results were compared to their clinical records. Results: Among 139 patients, 29% had confirmed bacterial infections and 5% viral infections. nCD64 and mCD169 respectively showed 88 and 86% sensitivity and 90 and 100% specificity for identifying subjects in bacterial or viral conditions. Conclusion: This point-of-care technique could allow better management of patients in the ED.

Tissue-Resident Macrophages Limit Pulmonary CD8 Resident Memory T Cell Establishment

Tissue resident memory CD8 T cells (T_RM) serve as potent local sentinels and contribute significantly to protective immunity against intracellular mucosal pathogens. While the molecular and transcriptional underpinnings of T_RM differentiation are emerging, how T_RM establishment is regulated by other leukocytes in vivo is largely unclear. Here, we observed that expression of PPAR-γ in the myeloid compartment was a negative regulator of CD8 T_RM establishment following influenza virus infection. Interestingly, myeloid deficiency of PPAR-γ resulted in selective impairment of the tissue-resident alveolar macrophage (AM) compartment during primary influenza infection, suggesting that AM are likely negative regulators of CD8 T_RM differentiation. Indeed, influenza-specific CD8 T_RM cell numbers were increased following early, but not late ablation of AM using the CD169-DTR model. Importantly, these findings were specific to the parenchyma of infected tissue as circulating memory T cell frequencies in lung and T_CM and T_EM in spleen were largely unaltered following macrophage ablation. Further, the magnitude of the effector response could not explain these observations. These data indicate local regulation of pulmonary T_RM differentiation is alveolar macrophage dependent. These, findings could aid in vaccine design aimed at increasing T_RM density to enhance protective immunity, or deflating their numbers in conditions where they cause overt or veiled chronic pathologies.

Maf expression in human macrophages and lymph node sinus macrophages in patients with esophageal cancer

The large Maf transcription factors are expressed in immune cells including macrophages and lymphocytes. To investigate the distribution of Maf expression in human organs, immunostaining for Maf was performed using sections of several human organs. High Maf expression was seen in the nucleus of macrophages in the gastrointestinal tract and lymph node sinus macrophages (LySMs). Then, we assessed whether Maf expression in LySMs was correlated with CD169 expression and the clinical prognosis in patients with esophageal cancer. Maf expression was associated with CD169 expression, but Maf expression in LySMs was not associated with the clinical course in patients with esophageal cancer. We determined which cytokines stimulate Maf expression using cultured macrophages. Immunocytochemistry showed that Maf expression was significantly elevated by interferon-γ. These results are the first report of Maf expression in human samples. Maf expression may be a marker for the macrophage population in humans.

Functional CD169 on Macrophages Mediates Interaction with Dendritic Cells for CD8+ T Cell Cross-Priming

Splenic CD169⁺ macrophages are located in the marginal zone to efficiently capture blood-borne pathogens. Here, we investigate the requirements for the induction of CD8⁺ T cell responses by antigens (Ags) bound by CD169⁺ macrophages. Upon Ag targeting to CD169⁺ macrophages, we show that BATF3-dependent CD8α⁺ dendritic cells (DCs) are crucial for DNGR-1-mediated cross-priming of CD8⁺ T cell responses. In addition, we demonstrate that CD169, a sialic acid binding lectin involved in cell-cell contact, preferentially binds to CD8α⁺ DCs and that Ag transfer to CD8α⁺ DCs and subsequent T cell activation is dependent on the sialic acid-binding capacity of CD169. Finally, functional CD169 mediates optimal CD8⁺ T cell responses to modified vaccinia Ankara virus infection. Together, these data indicate that the collaboration of CD169⁺ macrophages and CD8α⁺ DCs for the initiation of effective CD8⁺ T cell responses is facilitated by binding of CD169 to sialic acid containing ligands on CD8α⁺ DCs.

Lymph Node Subcapsular Sinus Macrophages as the Frontline of Lymphatic Immune Defense

Lymphatic vessels collect and transport lymph and pathogens to the draining lymph node (LN) to generate proper immune protection. A layer of macrophages that strategically line the LN subcapsular sinus (SCS) is directly exposed to the afferent lymph and are denoted as SCS macrophages. These macrophages are the frontline of immune defense that interact with lymph-borne antigens. The importance of these macrophages in limiting the spread of pathogens has been demonstrated in both viral and bacterial infection. In anti-microbial responses, these macrophages can directly or indirectly activate other LN innate immune cells to fight against pathogens, as well as activate T cells or B cells for adaptive immunity. As the first layer of immune cells embracing the tumor-derived antigens, SCS macrophages also actively participate in cancer immune regulation. Recent studies have shown that the LNs' SCS macrophage layer is interrupted in disease models. Despite their importance in fighting the spread of pathogens and in activating anti-tumor immunity, the mechanism and the immunological functional consequences for their disruption are not well-understood. Understanding the mechanism of these macrophages will enhance their capability for therapeutic targeting.