Complement Receptors and Their Role in Leukocyte Recruitment and Phagocytosis

Mac-1 regulates disease stage-specific immunosuppression via the nitric oxide pathway in autoimmune disease

Integrin Mac-1 plays a critical role in the development of multiple sclerosis (MS); however, the underlying mechanism is not fully understood. Here, we developed a myeloid-specific Mac-1-deficient mouse. Using an experimental autoimmune encephalomyelitis (EAE) mouse model of MS, we report that Mac-1 on myeloid cells is key to disease development. Our data reveal that myeloid-specific Mac-1 significantly increases EAE severity and hinders disease regression. Loss of Mac-1 increases Gr-1+ cells in peripheral tissues and the CNS and preferably accelerates the transition of Ly6Chi monocytes from a pro-inflammatory to an immunosuppressive phenotype in a disease stage-dependent manner. Mechanistically, our results demonstrate that Mac-1 suppresses interferon-γ production and prevents monocytes from acquiring immunosuppressive functions by reducing the expression of iNOS, IDO, and CD84. Administration of a NOS-specific inhibitor in Mac-1-deficient EAE mice abolishes disease regression. These insights could help develop Mac-1-targeting strategies for better treatment of MS.

Genetic and Epigenetic Dysregulation of CR1 is Associated with Catastrophic Antiphospholipid Syndrome (CAPS)

Objective

Catastrophic antiphospholipid syndrome (CAPS), characterized by widespread thrombosis and multi-organ failure, is associated with high morbidity and mortality. We previously established complement activation as a pathogenic driver of CAPS and identified rare germline variants in complement-regulatory genes including Complement Receptor 1 (CR1) in 50% of CAPS.

Methods

We quantified CR1 expression by flow cytometry across hematopoietic cell types. CRISPR/Cas9 genome editing of TF-1 (erythroleukemia) cells was performed to generate CR1 "knock-out" and "knock-in" lines with patient-specific CR1 variants. Multiomics analysis was performed to investigate the role of methylation in CR1 expression in patients with reduced CR1 expression. Functional impact of low CR1 expression was assessed by complement-mediated cell killing using modified Ham (mHam) assay, cell-bound complement degradation products through flow cytometry and circulatory immune complexes (CIC) in serum samples through ELISA.

Results

CR1 expression in erythrocytes was markedly reduced on CAPS erythrocytes (n=9, 21.80%) compared to healthy controls (HC; n=32, 82.40%), with promoter hypermethylation emerging as a plausible epigenetic mechanism for CR1 downregulation. A novel germline variant (CR1-V2125L; rs202148801) mitigated CR1 expression and increased complement-mediated cell death of knock-in cell lines. Erythrocytes from the patient with the CR1-V2125L variant had low CR1 expression. Levels of CIC, which are bound and cleared by CR1 on erythrocytes, were higher in acute CAPS (n=3, 25.55 μg Eq/ml) than healthy controls (n=3, 7.445 μg Eq/ml). Five patients were treated with C5 inhibition which mitigated thrombosis.

Conclusion

Genetic or epigenetic-mediated CR1 deficiency is a potential hallmark of CAPS and predicts response to C5 inhibition.

Engineering the Immune Response to Biomaterials

Biomaterials are increasingly used as implants in the body, but they often elicit tissue reactions due to the immune system recognizing them as foreign bodies. These reactions typically involve the activation of innate immunity and the initiation of an inflammatory response, which can persist as chronic inflammation, causing implant failure. To reduce these risks, various strategies have been developed to modify the material composition, surface characteristics, or mechanical properties of biomaterials. Moreover, bioactive materials have emerged as a new class of biomaterials that can induce desirable tissue responses and form a strong bond between the implant and the host tissue. In recent years, different immunomodulatory strategies have been incorporated into biomaterials as drug delivery systems. Furthermore, more advanced molecule and cell-based immunomodulators have been developed and integrated with biomaterials. These emerging strategies will enable better control of the immune response to biomaterials and improve the function and longevity of implants and, ultimately, the outcome of biomaterial-based therapies.

Inhibition of Alternative and Terminal Complement Pathway Components Modulate the Immune Response Against Bacteria and Fungi in Whole Blood

Complement activation plays a critical role in the inflammatory response to Escherichia coli and Aspergillus fumigatus conidia. However, the specific contributions of complement components, including anaphylatoxin receptors, remain unclear. Using an ex vivo lepirudin whole blood model, we examined the activation of all three complement pathways (C4c, C3bc, and sC5b-9) induced by these microbes. We also assessed granulocyte and monocyte receptor expression of CD11b, CD64, C3aR, C5aR1, and C5aR2, along with phagocytosis, leukocyte activation (MPO), and cytokine release. Additionally, we investigated selective inhibition of complement components FD, C3, C5, and C5aR1. Both microbes increased complement activation products (C3bc and sC5-9), CD11b and CD64 expression, MPO release, and proinflammatory cytokines (IL-1β, IL-6, IL-8, and TNF), while decreasing C3aR, C5aR1, and C5aR2 expression. Complement inhibition reduced CD11b and CD64 expression and partially restored C3aR and C5aR1 levels, with minimal effects on C5aR2. FD, C3, and C5 inhibition reduced downstream complement markers, with FD and C3 inhibition also reducing phagocytosis, and only C3 inhibition reducing MPO release. The cytokine response varied by microbe: E. coli triggered higher proinflammatory cytokines, and FD and C3 inhibition generally reduced cytokine release, while C5 inhibition was less effective. Interestingly, A. fumigatus-induced cytokines significantly increased with C5aR1 inhibition, highlighting immune response differences related to C5aR1 signalling in bacterial versus fungal infections. In conclusion, regulation of inflammation through FD, C3, C5, and C5aR1 underscores the immunoregulatory role of the complement system in anti-microbial immune responses.

Complement in Antibody-Mediated Rejection of the Kidney Graft: From Pathophysiology to Clinical Practice

Antibody-mediated rejection (AMR) is a leading cause of kidney graft failure. Complement activation is involved in the AMR process. Our aim is to provide the current understanding of the pathophysiology related to complement-mediated injury in AMR, to present the current evidence regarding complement blockade in AMR management, and to point out emerging therapies and future directions in this area. The complement system plays an important role in the onset and progression of AMR. There is a balance between complement-dependent and -independent mechanisms in the development of rejection lesions. Classic and leptin pathways are involved in this process. C4d positivity is no longer a mandatory feature for AMR diagnosis but remains an independent predictor of negative outcomes. The current evidence regarding AMR treatment is limited. Terminal and proximal complement blockade has gained recognition in clinical practice. Eculizumab and C1 inhibitors are effective in the treatment of AMR as adjuvant therapies to the standard of care. The availability of novel complement inhibitors will lead to more effective and tailored treatment strategies.

Adenosine 2B Receptor Signaling Impairs Vaccine-Mediated Protection Against Pneumococcal Infection in Young Hosts by Blunting Neutrophil Killing of Antibody-Opsonized Bacteria

Background/Objective: Neutrophils are essential for vaccine-mediated protection against pneumococcal infection and impairment in their antibacterial function contributes to reduced vaccine efficacy during aging. However, the signaling pathways that control the neutrophil responses in vaccinated hosts are not fully understood. The extracellular adenosine pathway is a known regulator of neutrophils in naïve hosts. The aim of this study was to test the role of this pathway in the function of neutrophils and their protection against infection upon vaccination as a function of the host's age. Methods: To test the role of adenosine in the antimicrobial activity of neutrophils against antibody-opsonized pneumococci, we used bone marrow-derived neutrophils isolated from wild-type or specific-adenosine-receptors knock-out mice. To measure the effect of adenosine receptor signaling in vivo, we treated vaccinated mice with agonists or antagonists that were specific to the different adenosine receptors prior to pulmonary challenge with pneumococci and assessed the bacterial burden and clinical score post-infection. Results: We found that signaling via the adenosine 2B (A2BR) receptor but not the A2A or A1 receptors diminished the intracellular pneumococcal killing following antibody-mediated uptake in young hosts. In vivo, the agonism of the A2BR receptor significantly worsened the pneumococcal infection outcomes in young, vaccinated mice. In contrast, A2BR signaling had no effect on the intracellular bacterial killing by neutrophils from aged mice. Further, in vivo A2BR inhibition had no effect on the pneumococcal disease progression in aged, vaccinated mice. Conclusions: A2BR signaling reduced pneumococcal vaccine-mediated protection by impairing the antimicrobial activity of neutrophils against antibody-opsonized bacteria in young hosts. However, inhibiting this pathway was not sufficient to boost responses in aged hosts.

Mechanism and regulation of the complement activity in kidney xenotransplantation

Xenotransplantation is emerging as one of several potential solutions for addressing organ donor shortages, with significant progress bringing it closer to clinical application. However, challenges remain, particularly concerning complement system dysregulation caused by species differences, as well as xenoantigens and coagulopathy. Complement regulatory proteins expressed on endothelial cells of donor xenografts are less compatible with complement components in recipients. These difficulties contribute to hyperacute rejection, characterized by antibody-mediated complement activation that destroys the graft within 24 h. Moreover, because molecules are incompatible across different species, ischemia-reperfusion injury or infection can easily elicit complement activity via all three pathways, resulting in xenograft loss via complement-mediated vascular injury. Complement activity also stimulate innate and adaptive immune cells. To address this issue, genetic modifications in donor pigs and the development of novel medicines have been tested in preclinical models with promising results. Pigs modified to express human complement-regulating molecules such as CD46, CD55, and CD59 have shown longer kidney xenograft survivals over years in preclinical models with nonhuman primates, paving the way for clinical trials. Anti-complement component agents such as C1 esterase and C5 inhibitors have also been shown to increase xenograft survivals. This review examines the role of the complement system in kidney xenotransplantation, emphasizing new research and clinical trial advancements.

The specific contributions of factor H and factor I in controlling fluid phase activation of the alternative complement pathway

The immediate defense provided by the alternative complement pathway (AP) is under constant control by fluid phase regulators, factor H (FH) and factor I (FI), to prevent nonessential activation. Removal of either FI or FH from serum results in spontaneous AP activation, although the extent of activation caused by separate removal of each regulator has not been compared. In purified protein reactions with < 25% normal FH levels, additions of 6-100% normal FI levels, did not reduce C3a, Ba or FB cleavage. In reactions with 100% FH: C3a was not generated; Ba and FB cleavage was 3-fold lower; and C3 inactivation increased 2-fold as FI concentrations doubled. In reactions with 100% FI, FH levels ≥ 25% reduced C3a and Ba levels. AP activation levels were also compared in FI-depleted and FH-depleted serum. After magnesium addition to FI-depleted serum, C3a remained unchanged and Ba increased 3-fold, whereas in FH-depleted serum, C3a increased 13-fold and Ba increased 20-fold. Addition of 100% FI protein to FI-depleted serum did not change C3a and Ba, whereas, 100% FH added to FH-depleted serum prevented all activation. We conclude that normal levels of FH are sufficient to compensate for FI deficiencies and prevent unnecessary fluid phase AP activation.

Action of the Terminal Complement Pathway on Cell Membranes

The complement pathway is one of the most ancient elements of the host's innate response and includes a set of protein effectors that rapidly react against pathogens. The late stages of the complement reaction are broadly categorised into two major outcomes. Firstly, C5a receptors, expressed on membranes of host cells, are activated by C5a to generate pro-inflammatory responses. Secondly, target cells are lysed by a hetero-oligomeric pore known as the membrane attack complex (MAC) that punctures the cellular membrane, causing ion and osmotic flux. Generally, several membrane-bound and soluble inhibitors protect the host membrane from complement damage. This includes inhibitors against the MAC, such as clusterin and CD59. This review addresses the most recent molecular and structural insights behind the activation and modulation of the integral membrane proteins, the C5a receptors (C5aR1 and C5aR2), as well as the regulation of MAC assembly. The second aspect of the review focuses on the molecular basis behind inflammatory diseases that are reflective of failure to regulate the terminal complement effectors. Although each arm is unique in its function, both pathways may share similar outcomes in these diseases. As such, the review outlines potential synergy and crosstalk between C5a receptor activation and MAC-mediated cellular responses.

Adenosine 2B receptor signaling impairs vaccine-mediated protection against pneumococcal infection in young hosts by blunting neutrophil killing of antibody opsonized bacteria

Background/Objective

Neutrophils are essential for vaccine-mediated protection against pneumococcal infection and impairment in their antibacterial function contributes to reduced vaccine efficacy during aging. However, the signaling pathways controlling neutrophil responses in vaccinated hosts are not fully understood. The extracellular adenosine pathway is a known regulator of neutrophils in naïve hosts. The aim of this study was to test the role of this pathway in neutrophil function and protection against infection upon vaccination across host age.

Methods

To test the role of adenosine in the antimicrobial activity of neutrophils against antibody-opsonized pneumococci, we used bone marrow derived neutrophils isolated from wild type or specific adenosine receptors knock-out mice. To measure the effect of adenosine receptor signaling in vivo , we treated vaccinated mice with agonists or antagonists specific to the different adenosine receptors prior to pulmonary challenge with pneumococci and assessed bacterial burden and clinical score post infection.

Results

We found that signaling via the adenosine 2B (A2BR) but not A2A or A1 receptor diminished intracellular pneumococcal killing following antibody-mediated uptake in young hosts. In vivo , agonism of A2BR significantly worsened pneumococcal infection outcome in young, vaccinated mice. In contrast, A2BR signaling had no effect on intracellular bacterial killing by neutrophils from aged mice. Further, in vivo A2BR inhibition had no effect on pneumococcal disease progression in aged, vaccinated mice.

Conclusions

A2BR signaling reduced pneumococcal vaccine-mediated protection by impairing neutrophil antimicrobial activity against antibody-opsonized bacteria in young hosts. However, inhibiting this pathway was not sufficient to boost responses in aged hosts.

Complement activation as a biomarker for platelet-activating antibodies in heparin-induced thrombocytopenia

BACKGROUND

Immunoglobulin G antibodies (Abs) to platelet factor 4 (PF4) complexed to heparin (PF4/H) commonly occur after H exposure but cause life-threatening complications of H-induced thrombocytopenia (HIT) in only a few patients. Presently, only platelet activation assays reliably distinguish anti-PF4/H Abs that cause disease (HIT Abs) from those likely to be asymptomatic (AAbs).

OBJECTIVES

Recent studies indicate that complement activation is an important serologic property of HIT Abs and is essential for IgG Fc receptor IIA-mediated cellular activation. As platelet activation by HIT Abs also relies on IgG Fc receptor IIA activation, we correlated the complement- and platelet-activating properties of anti-PF4/H Abs in a clinically annotated patient cohort.

METHODS

Clinical and laboratory features of patients with HIT (n = 8) and AAbs+ (n = 14) were correlated with properties of complement, platelet, and monocyte/neutrophil activation.

RESULTS

Expected clinical and laboratory differences were seen between HIT and AAb+ patients, with HIT patients having lower mean platelet counts, greater percentage drop in platelet counts, higher 4T and HIT expert probability scores, higher anti-PF4 polyclonal and immunoglobulin G Ab levels, and serotonin release assay positivity. Ex vivo assays revealed significant differences in complement activation by HIT vs AAb+ patients, with the extent of complement activation closely correlated with percent serotonin release by anti-PF4/H Abs and matrix metalloproteinase-9 and interleukin-8 release in whole blood.

CONCLUSION

These findings suggest that complement activation strongly correlates with cellular activation endpoints, including platelet and monocyte/neutrophil activation, and if confirmed in a larger prospective study, may serve as a "functional" biomarker for pathogenic HIT Abs.

Neutrophils in colorectal cancer: mechanisms, prognostic value, and therapeutic implications

Neutrophils, the most abundant myeloid cells in human peripheral blood, serve as the first defense line against infection and are also significantly involved in the initiation and progression of cancer. In colorectal cancer (CRC), neutrophils exhibit a dual function by promoting tumor events and exerting antitumor activity, which is related to the heterogeneity of neutrophils. The neutrophil extracellular traps (NETs), gut microbiota, and various cells within the tumor microenvironment (TME) are involved in shaping the heterogeneous function of neutrophils. This article provides an updated overview of the complex functions and underlying mechanisms of neutrophils in CRC and their pivotal role in guiding prognosis assessment and therapeutic strategies, aiming to offer novel insights into neutrophil-associated treatment approaches for CRC.

An in vitro nanocarrier-based B cell antigen loading system; tumor growth suppression via transfusion of the antigen-loaded B cells in vivo

B cell-based vaccines are expected to provide an alternative to DC-based vaccines. However, the efficacy of antigen uptake by B cells in vitro is relatively low, and efficient antigen-loading methods must be established before B cell-based vaccines are viable in clinical settings. We recently developed an in vitro system that efficiently loads antigens into isolated splenic B cells via liposomes decorated with hydroxyl PEG (HO-PEG-Lips). Therefore, the purpose of this study was to expand this system in order to achieve another approach to in vivo tumor growth suppression. By using HO-PEG-Lips as a carrier for model antigen OVA along with an adjuvant, α-galactosylceramide (GC), the amount of antigen loading to the B cells in vitro was increased compared with that of both free OVA and free GC. Transfusion of B cells treated with HO-PEG-Lips that encapsulated OVA and GC suppressed the growth of OVA-expressing murine thymoma (E.G7-OVA) tumors in vivo through strong induction of OVA-specific T cells. Under fluorescence microscopic observation, migration of the transfused B cells in the spleens of recipient mice were confirmed. Our results indicate that our novel antigen-loading system could become a promising approach to facilitate the development of cell-based therapeutic cancer vaccines utilizing B cells as alternative APCs.

In Vitro Infection of Human Macrophages with Porphyromonas gingivalis W83

This study aimed to investigate the innate immune response of human macrophages to Porphyromonas gingivalis W83 using a novel in vitro infection model. The growth kinetics of P. gingivalis W83 were analyzed, revealing an exponential growth phase at 8 h (optical density = 0.70). To establish a reliable macrophage model, the differentiation of THP-1 monocytes into macrophages was optimized using low concentrations of phorbol 12-myristate 13-acetate (PMA). This approach induced enhanced adherence and morphological changes, with full differentiation achieved after 48 h of PMA treatment followed by 24 h of rest. Polarization towards the pro-inflammatory M1 phenotype was successfully induced with interferon-γ (IFN-γ) and lipopolysaccharide (LPS), as confirmed using cytokine profiling. Cytokine analysis using Luminex® technology demonstrated significant increases in interleukin (IL)-1β, tumor necrosis factor-α (TNF-α), and IL-6, indicating the effective activation of macrophages towards a pro-inflammatory phenotype. Building upon this macrophage model, this study investigated the interactions between macrophages and P. gingivalis W83 during its exponential growth phase. After a one-hour infection period, bacterial DNA quantification in supernatants and lysed macrophages revealed minimal levels of internalized or adherent bacteria, supporting the hypothesis that P. gingivalis effectively evades immune detection. These findings emphasize the utility of this model in uncovering the sophisticated immune evasion strategies employed by P. gingivalis, with significant implications for the development of targeted therapeutic interventions.

The Therapeutic Efficacy and Molecular Mechanisms of Artemisia argyi Essential Oil in Treating Feline Herpesvirus Infection via Nasal Drops

This study aimed to explore the therapeutic potential and mechanisms of Artemisia argyi essential oil (AAEO) in managing feline herpesvirus type 1 (FeHV-1) infections. FeHV-1, the causative agent of feline viral rhinotracheitis (FVR), leads to severe respiratory and systemic complications in cats. In this study, 35 cats were divided into blank, FeHV-1 infection, and AAEO treatment groups (high, medium, and low doses). In vivo experiments demonstrated that AAEO alleviated clinical symptoms, reduced tissue damage, and modulated immune responses. The AAEO-treated groups showed higher survival rates, stabilized body temperatures, and less severe weight loss compared to the FeHV-1 group. Histopathological analysis revealed improved integrity in nasal, tracheal, and bronchial tissues. Transcriptomic and proteomic analyses identified critical pathways, such as IL-17 signaling, influenced by AAEO treatment, highlighting its role in suppressing inflammation and protecting tissue integrity. In vitro assays revealed that AAEO has concentration-dependent cytotoxicity in feline kidney cells (F81) and provides protective effects when used as a pre-treatment. These findings suggest that AAEO enhances host immune defenses and mitigates FeHV-1-induced damage through immune modulation and tissue protection.

N-terminomics profiling of host proteins targeted by excretory-secretory proteases of the nematode Angiostrongylus vasorum identifies points of interaction with canine coagulation and complement cascade

The cardiopulmonary nematode Angiostrongylus vasorum can cause severe disease in dogs, including coagulopathies manifesting with bleeding. We analysed A. vasorum excretory/secretory protein (ESP)-treated dog plasma and serum by N-terminome analysis using Terminal Amine Isotopic Labelling of Substrates (TAILS) to identify cleaved host substrates. In plasma and serum samples 430 and 475 dog proteins were identified, respectively. A total of eight dog proteins were significantly cleaved at higher levels upon exposure to A. vasorum ESP: of these, three were coagulation factors (factor II, V and IX) and three were complement proteins (complement C3, C4-A and C5). Comparison with human motif sequence orthologues revealed known cleavage sites in coagulation factor IX and II (prothrombin). These and further identified cleavage sites suggest direct or indirect activation or proteolysis of complement and coagulation components through A. vasorum ESP, which contains several proteases. Further studies are needed to validate their substrate specificity.

Complement activation drives the phagocytosis of necrotic cell debris and resolution of liver injury

Cells die by necrosis due to excessive chemical or thermal stress, leading to plasma membrane rupture, release of intracellular components and severe inflammation. The clearance of necrotic cell debris is crucial for tissue recovery and injury resolution, however, the underlying mechanisms are still poorly understood, especially in vivo. This study examined the role of complement proteins in promoting clearance of necrotic cell debris by leukocytes and their influence on liver regeneration. We found that independently of the type of necrotic liver injury, either acetaminophen (APAP) overdose or thermal injury, complement proteins C1q and (i)C3b were deposited specifically on necrotic lesions via the activation of the classical pathway. Importantly, C3 deficiency led to a significant accumulation of necrotic debris and impairment of liver recovery in mice, which was attributed to decreased phagocytosis of debris by recruited neutrophils in vivo. Monocytes and macrophages also took part in debris clearance, although the necessity of C3 and CD11b was dependent on the specific type of necrotic liver injury. Using human neutrophils, we showed that absence of C3 or C1q caused a reduction in the volume of necrotic debris that is phagocytosed, indicating that complement promotes effective debris uptake in mice and humans. Moreover, internalization of opsonized debris induced the expression of pro-resolving genes in a C3-dependent manner, supporting the notion that debris clearance favors the resolution of inflammation. In summary, complement activation at injury sites is a pivotal event for necrotic debris clearance by phagocytes and determinant for efficient recovery from tissue injury.

Neutrophil diversity and function in health and disease

Neutrophils, the most abundant type of granulocyte, are widely recognized as one of the pivotal contributors to the acute inflammatory response. Initially, neutrophils were considered the mobile infantry of the innate immune system, tasked with the immediate response to invading pathogens. However, recent studies have demonstrated that neutrophils are versatile cells, capable of regulating various biological processes and impacting both human health and disease. Cytokines and other active mediators regulate the functional activity of neutrophils by activating multiple receptors on these cells, thereby initiating downstream signal transduction pathways. Dysfunctions in neutrophils and disruptions in neutrophil homeostasis have been implicated in the pathogenesis of numerous diseases, including cancer and inflammatory disorders, often due to aberrant intracellular signaling. This review provides a comprehensive synthesis of neutrophil biological functions, integrating recent advancements in this field. Moreover, it examines the biological roles of receptors on neutrophils and downstream signaling pathways involved in the regulation of neutrophil activity. The pathophysiology of neutrophils in numerous human diseases and emerging therapeutic approaches targeting them are also elaborated. This review also addresses the current limitations within the field of neutrophil research, highlighting critical gaps in knowledge that warrant further investigation. In summary, this review seeks to establish a comprehensive and multidimensional model of neutrophil regulation, providing new perspectives for potential clinical applications and further research.

Complement component 5a receptor 1 and leukotriene B4 receptor 1 regulate neutrophil extracellular trap (NET) formation through Rap1a/B-Raf/ERK signaling pathway and their deficiency in term low birth weight newborns leads to deficient NETosis

BACKGROUND

Neutrophil extracellular traps (NETs) being one of the predominant activities of neutrophils has become its key defense mechanism owing to its extensive role in inflammation and infection. However, the mechanisms regulating NET formation or NETosis still remains to be better understood. Our earlier whole genome transcriptomic data revealed two G-protein couple receptors (GPCRs) - complement component 5a receptor 1 (C5aR1) and leukotriene B4 receptor 1 (LTB4R1) were downregulated in term low birth weight (tLBW) newborns with deficient NET formation abilities. Neutrophils employ C5aR1 and LTB4R1 for mediating their immune responses, inflammation and antimicrobial activity. Hence, this study was aimed to explore the role of two GPCRs, C5aR1 and LTB4R1 including their downstream signaling molecules in NETs induction and regulation.

METHODS

The validation of the transcriptomic data for C5aR1 and LTB4R1 was done using quantitative real time PCR. Pharmacological inhibition of C5aR1 and LTB4R1 using W-54011 and LY223982 on neutrophils of adults and newborns' was done to study their impact on NETosis. Extracellular DNA release, Reactive oxygen species (ROS) generation, expression of NET proteins, and signaling molecules downstream to C5aR1 and LTB4R1 were quantified using plate reader based assay, immunofluorescence, and western blotting. Myeloperoxidase (MPO)-DNA quantified by flow cytometry. Knockdown studies using siRNA against C5aR1 and LTB4R1 were done in HL-60 cells derived surrogate neutrophils and expression of downstream molecules of the two GPCRs, C5aR1 and LTB4R1 signaling axis along with NET proteins was quantified by western blotting.

RESULTS

The expression of C5aR1 and LTB4R1, extracellular DNA, ROS and NET associated proteins (NE, CitH3, PAD4 and MPO) was notably increased upon NET induction in healthy adults and normal birth weight (NBW) newborns' neutrophils. Pharmacological inhibition of these two GPCRs led to substantial reduction in NETosis, extracellular DNA, ROS generation, and expression of NET associated proteins like CitH3, NE, PAD4, MPO along with downstream signaling molecules Rap1a, B-Raf and pERK. Our observations suggest a precise role of C5aR1 and LTB4R1 on induction of NETs via Rap1a/B-Raf/ERK signaling axis.

CONCLUSION

The C5aR1 and LTB4R1 signaling via Rap1a/B-Raf/ERK axis acts as a signal-relay mechanism to regulate NET formation in neutrophils. Further, C5aR1 and LTB4R1 signaling cascade along with NET-associated proteins are remarkably downregulated in tLBW newborns' neutrophils leading to impaired NETosis in them. Therefore, C5aR1 and LTB4R1 and their signaling molecules could provide an effective therapeutic target for compromised NETosis like tLBW newborns.

Proteogenomic analysis of human cerebrospinal fluid identifies neurologically relevant regulation and implicates causal proteins for Alzheimer's disease

The integration of quantitative trait loci (QTLs) with disease genome-wide association studies (GWASs) has proven successful in prioritizing candidate genes at disease-associated loci. QTL mapping has been focused on multi-tissue expression QTLs or plasma protein QTLs (pQTLs). We generated a cerebrospinal fluid (CSF) pQTL atlas by measuring 6,361 proteins in 3,506 samples. We identified 3,885 associations for 1,883 proteins, including 2,885 new pQTLs, demonstrating unique genetic regulation in CSF. We identified CSF-enriched pleiotropic regions on chromosome (chr)3q28 near OSTN and chr19q13.32 near APOE that were enriched for neuron specificity and neurological development. We integrated our associations with Alzheimer's disease (AD) through proteome-wide association study (PWAS), colocalization and Mendelian randomization and identified 38 putative causal proteins, 15 of which have drugs available. Finally, we developed a proteomics-based AD prediction model that outperforms genetics-based models. These findings will be instrumental to further understand the biology and identify causal and druggable proteins for brain and neurological traits.

Specific surface-modified iron oxide nanoparticles trigger complement-dependent innate and adaptive antileukaemia immunity

Considerable advances have been achieved in the application of nanomaterials for immunotherapies, yet the precise immune effects induced by protein corona remain elusive. Here, we explore the formation mechanism and immune regulation process of protein corona in acute myeloid leukaemia (AML) mouse models using commercialized iron oxide nanoparticles (IONPs), with different surface modifications, including an FDA-approved variant. Using macrophages depleted or Complement Component 3 (C3) knockout mice, we demonstrate that carboxymethyl dextran-coated IONP (IONP-COOH) reduces leukaemia burden. Mechanistically, IONP-COOH indirectly binds to C3b after activating the complement alternative pathway, subsequently enhancing phagocytosis of macrophages and activating adaptive immunity mediated by complement corona. While aminated dextran-coated IONPs directly absorb C3b and activate the lectin pathway, leading to immune cell exhaustion. Our findings suggest that IONP-COOH may serve as an immune activator for AML treatment, offering a promising approach to developing therapeutic nanomaterials by leveraging surface chemistry to enhance immunotherapy.

Modulation of Monocyte Effector Functions and Gene Expression by Human Cytomegalovirus Infection

Monocytes are crucial players in innate immunity. The human cytomegalovirus (CMV) infection has significant impacts on monocyte effector functions and gene expression. CMV, a β-herpesvirus, disrupts key monocyte roles, including phagocytosis, antigen presentation, cytokine production, and migration, impairing their ability to combat pathogens and activate adaptive immune responses. CMV modulates monocyte gene expression, decreasing their capacity for antigen presentation and phagocytosis while increasing pro-inflammatory cytokine production, which can contribute to tissue damage and chronic inflammation. CMV also alters monocyte migration to sites of infection while promoting trans-endothelial migration, thus aiding viral dissemination. Additionally, the virus affects reactive oxygen species (ROS) production, thereby contributing to end-organ disease associated with CMV infection. Overall, these changes enhance viral persistence during acute infection and facilitate immune evasion during latency. We highlight the clinical significance of these disruptions, particularly in immunocompromised patients such as transplant recipients, where the modulation of monocyte function by CMV exacerbates risks for infection, inflammation, and graft rejection. An understanding of these mechanisms will inform therapeutic strategies to mitigate CMV-related complications in vulnerable populations.

Revealing the molecular landscape of calcium oxalate renal calculi utilizing a tree shrew model: a transcriptomic analysis of the kidney

Our comprehensive genomic investigation employing tree shrew calcium oxalate stone models unveils intricate links between kidney stone formation and diverse physiological systems. We identify a constellation of genes whose expression patterns point to multifaceted interactions among cardiovascular health, renal fibrosis, and bone homeostasis in the pathogenesis of renal calculi. Key players include CHIT1, TNFRSF18, CLEC4E, RGS1, DCSTAMP, and SLC37A2, which emerge as pivotal actors in arteriosclerosis, renal fibrosis, and osteoclastogenesis respectively, showcasing the complexity of stone disease. The downregulation of ADRA1D, LVRN, and ABCG8 underscores roles in urodynamics, epithelial-mesenchymal transition, and vitamin D metabolism, linking these to nephrolithiasis. Comparative genomics across tree shrew, human (Randall's plaque), rat, and mouse identifies shared KEGG pathways including Calcium signaling, Actin cytoskeleton regulation, Neuroactive ligand-receptor interactions, Complement and coagulation cascades, TRP channel regulation by inflammatory mediators, p53 signaling, and Fc gamma R-mediated phagocytosis. These pathways underscore the interconnectedness of immune, inflammatory, and metabolic processes in stone development. Our findings suggest novel targets for future therapeutics and prevention strategies against nephrolithiasis, highlighting the need for a holistic view of the disease encompassing multiple pathogenic factors.

Collagen binding adhesin restricts Staphylococcus aureus skin infection

Staphylococcus aureus causes approximately 80% of skin and soft tissue infections (SSTIs). Collagen is the most abundant human extracellular matrix protein with critical roles in wound healing, and S. aureus encodes a collagen binding adhesin (Cna). The role of this protein during skin infections is unknown. Here we report that inability to bind collagen results in worsened pathology of intradermal Δcna S. aureus infection. WT/Cna+ S. aureus showed reduced infection severity, aggregate formation, and significantly improved clearance of bacteria. Cna binds to the collagen-like domain of serum C1q protein to reduce its opsonophagocytic functions. We demonstrate that infection of C1qKO mice with WT bacteria show results similar to the Δcna group. Conversely, inability to bind collagen resulted in an amplified inflammatory response caused in part by macrophage and neutrophil small molecule mediators released at the infection site (MMP-9, MMP-12, LTB4), resulting in increased immune cell infiltration and death.

C3 glomerulopathy: a kidney disease mediated by alternative pathway deregulation

C3 glomerulopathy (C3G) is an ultra-rare complement-mediated kidney disease caused by to the deregulation of the alternative pathway (AP) of proximal complement. Consequently, all effector loops of the complement are active and can lead to pathologies, such as C3a- and C5a-mediated inflammation, C3b opsonization, surface C3b-mediated AP C3 convertase assembly, C3 cleavage product deposition in the glomerulus, and lytic C5b-9/MAC cell damage. The most common pathologic mechanisms are defective chronic alternative pathway deregulation, mostly occurring in the plasma, often causing C3 consumption, and chronic complement-mediated glomerular damage. C3G develops over several years, and loss of renal function occurs in more than 50% of patients. C3G is triggered by both genetic and autoimmune alterations. Genetic causes include mutations in individual complement genes and chromosomal variations in the form of deletions and duplications affecting genes encoding complement modulators. Many genetic aberrations result in increased AP C3 convertase activity, either due to decreased activity of regulators, increased activity of modulators, or gain-of-function mutations in genes encoding components of the convertase. Autoimmune forms of C3G do also exist. Autoantibodies target individual complement components and regulators or bind to neoepitopes exposed in the central alternative pathway C3 convertase, thereby increasing enzyme activity. Overactive AP C3 convertase is common in C3G patients. Given that C3G is a complement disease mediated by defective alternative pathway action, complement blockade is an emerging concept for therapy. Here, we summarize both the causes of C3G and the rationale for complement inhibition and list the inhibitors that are being used in the most advanced clinical trials for C3G. With several inhibitors in phase II and III trials, it is expected that effectice treatment for C3G will become availabe in the near future.

Complement C3 deficient mice show more severe imiquimod-induced psoriasiform dermatitis than wild-type mice regardless of the commensal microbiota

The complement active product, C3a, and the receptor C3aR comprise an axis that exerts various biological functions, such as protection against infection. C3a is highly expressed in the inflamed skin and blood from patients with psoriasiform dermatitis. However, the role of the C3a/C3aR axis in psoriasiform dermatitis remains unclear because conflicting results using C3-/- mice have been published. In this study, to elucidate the contribution of commensal microbiota in C3-/- and wild-type (WT) mice were subjected to imiquimod-induced psoriasiform dermatitis under different housing conditions. C3-/- mice showed increased epidermal thickness and keratinocyte proliferation markers in the inflamed ear compared to WT mice upon treatment with IMQ. These inflamed phenotypes were observed in both cohoused and separately housed conditions, and antibiotic treatment did not abolish the aggravation of IMQ-induced psoriasiform dermatitis in C3-/- mice. These results suggested that the difference of commensal microbiota is not important for the C3-involved psoriasiform dermatitis. Keratinocyte hyperproliferation is a major feature of the inflamed skin in patients with psoriasiform dermatitis. In vitro experiments showed that C3a and C3aR agonists inhibited keratinocyte proliferation, which was abolished by introduction of a C3aR antagonist. Collectively, these results suggest that the C3a/C3aR axis plays a critical role in psoriasiform dermatitis development by inhibiting keratinocyte proliferation, regardless of the regulation of the commensal microbiota.

Immunity and Coagulation in COVID-19

Discovered in late 2019, the SARS-CoV-2 coronavirus has caused the largest pandemic of the 21st century, claiming more than seven million lives. In most cases, the COVID-19 disease caused by the SARS-CoV-2 virus is relatively mild and affects only the upper respiratory tract; it most often manifests itself with fever, chills, cough, and sore throat, but also has less-common mild symptoms. In most cases, patients do not require hospitalization, and fully recover. However, in some cases, infection with the SARS-CoV-2 virus leads to the development of a severe form of COVID-19, which is characterized by the development of life-threatening complications affecting not only the lungs, but also other organs and systems. In particular, various forms of thrombotic complications are common among patients with a severe form of COVID-19. The mechanisms for the development of thrombotic complications in COVID-19 remain unclear. Accumulated data indicate that the pathogenesis of severe COVID-19 is based on disruptions in the functioning of various innate immune systems. The key role in the primary response to a viral infection is assigned to two systems. These are the pattern recognition receptors, primarily members of the toll-like receptor (TLR) family, and the complement system. Both systems are the first to engage in the fight against the virus and launch a whole range of mechanisms aimed at its rapid elimination. Normally, their joint activity leads to the destruction of the pathogen and recovery. However, disruptions in the functioning of these innate immune systems in COVID-19 can cause the development of an excessive inflammatory response that is dangerous for the body. In turn, excessive inflammation entails activation of and damage to the vascular endothelium, as well as the development of the hypercoagulable state observed in patients seriously ill with COVID-19. Activation of the endothelium and hypercoagulation lead to the development of thrombosis and, as a result, damage to organs and tissues. Immune-mediated thrombotic complications are termed "immunothrombosis". In this review, we discuss in detail the features of immunothrombosis associated with SARS-CoV-2 infection and its potential underlying mechanisms.

Chitosan/hesperidin nanoparticles formulation: a promising approach against ethanol-induced gastric ulcers via Sirt1/FOXO1/PGC-1α/HO-1 pathway

Hesperidin (Hes) protects different organs from damage by acting as a potent antioxidant and anti-inflammatory. This study aims to evaluate the gastroprotective effects of free hesperidin and its chitosan nanoparticles (HNPs) against ethanol-induced gastric ulcers in rats, hypothesizing that HNPs will enhance bioavailability and therapeutic efficacy due to improved solubility and targeted delivery. HNPs were synthesized via ion gelation and characterized using TEM, SEM, and zeta potential analyses. Key assessments included gastric acidity, histological analysis, and markers of inflammation, oxidative stress, and apoptosis. HNPs significantly decreased gastric acidity, reduced inflammatory and apoptotic markers, and enhanced antioxidant enzyme activities compared to free hesperidin and esomeprazole. Furthermore, Sirt-1, PGC-1α, HO-1, and FOXO1 gene expression were also evaluated. HNPs raised Sirt-1, PGC-1α, HO-1, and downregulated FOXO1, and they suppressed the activities of NF-κB p65, COX-2, IL-1β, CD86, FOXO1 P53, and caspase-3 and increased Sirt-1 activity. HNPs treatment notably restored antioxidant enzyme activity, reduced oxidative stress and inflammatory markers, and improved histological outcomes more effectively than free hesperidin and esomeprazole. These results indicate that chitosan nanoparticles significantly enhance the gastroprotective effects of hesperidin against ethanol-induced gastric ulcers, potentially offering a more effective therapeutic strategy. Further research should explore the clinical applications of HNPs in human subjects.

The Promise of Complement Therapeutics in Solid Organ Transplantation

Transplantation is the ideal therapy for end-stage organ failure, but outcomes for all transplant organs are suboptimal, underscoring the need to develop novel approaches to improve graft survival and function. The complement system, traditionally considered a component of innate immunity, is now known to broadly control inflammation and crucially contribute to induction and function of adaptive T-cell and B-cell immune responses, including those induced by alloantigens. Interest of pharmaceutical industries in complement therapeutics for nontransplant indications and the understanding that the complement system contributes to solid organ transplantation injury through multiple mechanisms raise the possibility that targeting specific complement components could improve transplant outcomes and patient health. Here, we provide an overview of complement biology and review the roles and mechanisms through which the complement system is pathogenically linked to solid organ transplant injury. We then discuss how this knowledge has been translated into novel therapeutic strategies to improve organ transplant outcomes and identify areas for future investigation. Although the clinical application of complement-targeted therapies in transplantation remains in its infancy, the increasing availability of new agents in this arena provides a rich environment for potentially transformative translational transplant research.

Disturbed Complement Receptor Expression Pattern of B Cells Is Enhanced by Toll-like Receptor CD180 Ligation in Diffuse Cutaneous Systemic Sclerosis

Autoantibody production is a hallmark of systemic sclerosis (SSc) and the most extensively studied role of B cells in the pathogenesis of the disease. However, the potential involvement of innate immune molecules in B-cell dysfunction in SSc is less understood. B-cell activation is an early event in the pathogenesis of SSc and is influenced by complement receptors (CRs) and Toll-like receptors (TLRs), shaping antibody responses. CR2 and CR1 modulate B-cell activation, and the roles of CR3 and CR4 are associated with autoimmune conditions. We investigated the expression of CRs in B cells from patients with the more severe form of the disease, diffuse cutaneous SSc (dcSSc), and the effect of TLR CD180 ligation on their expression. We found no significant difference in the basal expression of CD21 and CD11c in B cells between dcSSc and healthy controls (HCs). However, reduced basal CD11b expression in B cells in dcSSc compared to HCs, accompanied by a decrease in CD35 and an increase in CD11c expression following CD180 ligation may promote plasma cell formation and autoantibody production. Additionally, we searched for correlations between dcSSc-associated anti-DNA topoisomerase I (Scl-70) autoantibody, anti-citrate synthase (CS) natural autoantibody and complement component 3 (C3) levels and found a negative correlation between C3 and anti-CS autoantibody in dcSSc but not in HCs, supporting the hypothesis that natural autoantibodies could activate the complement system contributing to tissue injury in SSc.

Hydrogel crosslinking modulates macrophages, fibroblasts, and their communication, during wound healing

Biomaterial wound dressings, such as hydrogels, interact with host cells to regulate tissue repair. This study investigates how crosslinking of gelatin-based hydrogels influences immune and stromal cell behavior and wound healing in female mice. We observe that softer, lightly crosslinked hydrogels promote greater cellular infiltration and result in smaller scars compared to stiffer, heavily crosslinked hydrogels. Using single-cell RNA sequencing, we further show that heavily crosslinked hydrogels increase inflammation and lead to the formation of a distinct macrophage subpopulation exhibiting signs of oxidative activity and cell fusion. Conversely, lightly crosslinked hydrogels are more readily taken up by macrophages and integrated within the tissue. The physical properties differentially affect macrophage and fibroblast interactions, with heavily crosslinked hydrogels promoting pro-fibrotic fibroblast activity that drives macrophage fusion through RANKL signaling. These findings suggest that tuning the physical properties of hydrogels can guide cellular responses and improve healing, offering insights for designing better biomaterials for wound treatment.

Microglia undergo sex-dimorphic transcriptional and metabolic rewiring during aging

Microglia, the brain's resident macrophages, maintain brain homeostasis and respond to injury and infection. During aging they undergo functional changes, but the underlying mechanisms and their contributions to neuroprotection versus neurodegeneration are unclear. Previous studies suggested that microglia are sex dimorphic, so we compared microglial aging in mice of both sexes. RNA-sequencing of hippocampal microglia revealed more aging-associated changes in female microglia than male microglia, and more sex differences in old microglia than young microglia. Pathway analyses and subsequent validation assays revealed a stronger AKT-mTOR-HIF1α-driven shift to glycolysis among old female microglia and indicated that C3a production and detection was elevated in old microglia, especially in females. Recombinant C3a induced AKT-mTOR-HIF1α signaling and increased the glycolytic and phagocytic activity of young microglia. Single cell analyses attributed the aging-associated sex dimorphism to more abundant disease-associated microglia (DAM) in old female mice than old male mice, and evaluation of an Alzheimer's Disease mouse model revealed that the metabolic and complement changes are also apparent in the context of neurodegenerative disease and are strongest in the neuroprotective DAM2 subset. Collectively, our data implicate autocrine C3a-C3aR signaling in metabolic reprogramming of microglia to neuroprotective DAM during aging, especially in females, and also in Alzheimer's Disease.

Defective interferon signaling in the circulating monocytes of type 2 diabetic mice

Type 2 diabetes mellitus (T2DM) is associated with poor outcome after stroke. Peripheral monocytes play a critical role in the secondary injury and recovery of damaged brain tissue after stroke, but the underlying mechanisms are largely unclear. To investigate transcriptome changes and molecular networks across monocyte subsets in response to T2DM and stroke, we performed single-cell RNA-sequencing (scRNAseq) from peripheral blood mononuclear cells and bulk RNA-sequencing from blood monocytes from four groups of adult mice, consisting of T2DM model db/db and normoglycemic control db/+ mice with or without ischemic stroke. Via scRNAseq we found that T2DM expands the monocyte population at the expense of lymphocytes, which was validated by flow cytometry. Among the monocytes, T2DM also disproportionally increased the inflammatory subsets with Ly6C+ and negative MHC class II expression (MO.6C+II-). Conversely, monocytes from control mice without stroke are enriched with steady-state classical monocyte subset of MO.6C+II+ but with the least percentage of MO.6C+II- subtype. Apart from enhancing inflammation and coagulation, enrichment analysis from both scRNAseq and bulk RNAseq revealed that T2DM specifically suppressed type-1 and type-2 interferon signaling pathways crucial for antigen presentation and the induction of ischemia tolerance. Preconditioning by lipopolysaccharide conferred neuroprotection against ischemic brain injury in db/+ but not in db/db mice and coincided with a lesser induction of brain Interferon-regulatory-factor-3 in the brains of the latter mice. Our results suggest that the increased diversity and altered transcriptome in the monocytes of T2DM mice underlie the worse stroke outcome by exacerbating secondary injury and potentiating stroke-induced immunosuppression.

Significance Statement

The mechanisms involved in the detrimental diabetic effect on stroke are largely unclear. We show here, for the first time, that peripheral monocytes have disproportionally altered the subsets and changed transcriptome under diabetes and/or stroke conditions. Moreover, genes in the IFN-related signaling pathways are suppressed in the diabetic monocytes, which underscores the immunosuppression and impaired ischemic tolerance under the T2DM condition. Our data raise a possibility that malfunctioned monocytes may systemically and focally affect the host, leading to the poor outcome of diabetes in the setting of stroke. The results yield important clues to molecular mechanisms involved in the detrimental diabetic effect on stroke outcome.

Efferocytosis: Unveiling its potential in autoimmune disease and treatment strategies

Efferocytosis is a crucial process whereby phagocytes engulf and eliminate apoptotic cells (ACs). This intricate process can be categorized into four steps: (1) ACs release "find me" signals to attract phagocytes, (2) phagocytosis is directed by "eat me" signals emitted by ACs, (3) phagocytes engulf and internalize ACs, and (4) degradation of ACs occurs. Maintaining immune homeostasis heavily relies on the efficient clearance of ACs, which eliminates self-antigens and facilitates the generation of anti-inflammatory and immunosuppressive signals that maintain immune tolerance. However, any disruptions occurring at any of the efferocytosis steps during apoptosis can lead to a diminished efficacy in removing apoptotic cells. Factors contributing to this inefficiency encompass dysregulation in the release and recognition of "find me" or "eat me" signals, defects in phagocyte surface receptors, bridging molecules, and other signaling pathways. The inadequate clearance of ACs can result in their rupture and subsequent release of self-antigens, thereby promoting immune responses and precipitating the onset of autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, type 1 diabetes, and multiple sclerosis. A comprehensive understanding of the efferocytosis process and its implications can provide valuable insights for developing novel therapeutic strategies that target this process to prevent or treat autoimmune diseases.

Challenges of mesenchymal stem cells in the clinical treatment of COVID-19

The 2019 coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has brought an enormous public health burden to the global society. The duration of the epidemic, the number of infected people, and the widespread of the epidemic are extremely rare in modern society. In the initial stage of infection, people generally show fever, cough, and dyspnea, which can lead to pneumonia, acute respiratory syndrome, kidney failure, and even death in severe cases. The strong infectivity and pathogenicity of SARS-CoV-2 make it more urgent to find an effective treatment. Mesenchymal stem cells (MSCs) are a kind of pluripotent stem cells with the potential for self-renewal and multi-directional differentiation. They are widely used in clinical experiments because of their low immunogenicity and immunomodulatory function. Mesenchymal stem cell-derived exosomes (MSC-Exo) can play a physiological role similar to that of stem cells. Since the COVID-19 pandemic, a series of clinical trials based on MSC therapy have been carried out. The results show that MSCs are safe and can significantly improve patients' respiratory function and prognosis of COVID-19. Here, the effects of MSCs and MSC-Exo in the treatment of COVID-19 are reviewed, and the clinical challenges that may be faced in the future are clarified.

Immune Cell Migration to Cancer

Immune cell migration is required for the development of an effective and robust immune response. This elegant process is regulated by both cellular and environmental factors, with variables such as immune cell state, anatomical location, and disease state that govern differences in migration patterns. In all cases, a major factor is the expression of cell surface receptors and their cognate ligands. Rapid adaptation to environmental conditions partly depends on intrinsic cellular immune factors that affect a cell's ability to adjust to new environment. In this review, we discuss both myeloid and lymphoid cells and outline key determinants that govern immune cell migration, including molecules required for immune cell adhesion, modes of migration, chemotaxis, and specific chemokine signaling. Furthermore, we summarize tumor-specific elements that contribute to immune cell trafficking to cancer, while also exploring microenvironment factors that can alter these cellular dynamics within the tumor in both a pro and antitumor fashion. Specifically, we highlight the importance of the secretome in these later aspects. This review considers a myriad of factors that impact immune cell trajectory in cancer. We aim to highlight the immunotherapeutic targets that can be harnessed to achieve controlled immune trafficking to and within tumors.

Complement inhibitors in pediatric kidney diseases: new therapeutic opportunities

Historically, the complement system (classical, lectin, alternative, and terminal pathways) is known to play a crucial role in the etiopathogenesis of many kidney diseases. Direct or indirect activation in these settings is revealed by consumption of complement proteins at the serum level and kidney tissue deposition seen by immunofluorescence and electron microscopy. The advent of eculizumab has shown that complement inhibitors may improve the natural history of certain kidney diseases. Since then, the number of available therapeutic molecules and experimental studies on complement inhibition has increased exponentially. In our narrative review, we give a summary of the main complement inhibitors that have completed phase II and phase III studies or are currently used in adult and pediatric nephrology. The relevant full-text works, abstracts, and ongoing trials (clinicaltrials.gov site) are discussed. Data and key clinical features are reported for eculizumab, ravulizumab, crovalimab, avacopan, danicopan, iptacopan, pegcetacoplan, and narsoplimab. Many of these molecules have been shown to be effective in reducing proteinuria and stabilizing kidney function in different complement-mediated kidney diseases. Thanks to their efficacy and target specificity, these novel drugs may radically improve the outcome of complement-mediated kidney diseases, contributing to an improvement in our understanding of their underlying pathophysiology.

A2M possesses anti-bacterial functions by recruiting and enhancing phagocytosis through GRP78 in an echinoderm

Alpha-2-macroglobulin (A2M) is an extracellular macromolecule mainly known for its role as a broad-spectrum protease inhibitor in mammals. However, the immune recognition and regulation mechanisms of A2M in invertebrates are still not well investigated. In the current study, the role of sea cucumber Apostichopus japonicus A2M in the regulation of innate immune responses was explored. We found that AjA2M promotes phagocytosis of Vibrio splendidus in coelomocytes of sea cucumber. Then two major functional structural domains of AjA2M, the thioester domain (TED) and the receptor-binding structural domain (RBD) were cloned. It was found that the AjA2M-TED binds to pathogens while causing Vibrio splendidus aggregation; the AjA2M-RBD interacts with the Glucose Regulated Protein 78 (AjGRP78), subsequently AjGRP78 accelerates the degradation of Vibrio splendidus in lysosomes by facilitating polymerisation and rearrangement of the cytoskeleton. Collectively, the findings together suggest that A2M-GRP78 axis mediates immune signaling pathway of phagocytosis and AjA2M has been characterized to play an essential crucial role in antibacterial immune responses of invertebrates.

Porphyromonas gingivalis Strain W83 Infection Induces Liver Injury in Experimental Alcohol-Associated Liver Disease (ALD) in Mice

The liver plays a vital role in the defense against infections. Porphyromonas gingivalis (P. gingivalis), a dominant etiologic oral bacterium implicated in periodontal disease (PD), has been associated with various systemic diseases. This study aimed to investigate the influence of P. gingivalis on alcohol-associated liver diseases (ALD). Mice were fed a Lieber–DeCarli liquid diet containing 5% ethanol for 10 days after an initial adaptation period on a diet with lower ethanol content for 7 days. Two days before tissue sample collection, the mice were administered P. gingivalis strain W83 (Pg) through intraperitoneal injection (IP). Pair-fed mice with Pg infection (PF+Pg) exhibited an activated immune response to combat infections. However, alcohol-fed mice with Pg infection (AF+Pg) showed liver injury with noticeable abscess lesions and elevated serum alanine aminotransferase (ALT) levels. Additionally, these mice displayed liver infiltration of inflammatory monocytes and significant downregulation of proinflammatory cytokine gene expression levels; and AF+Pg mice also demonstrated increased intrahepatic neutrophil infiltration, as confirmed by chloroacetate esterase (CAE) staining, along with elevated gene expression levels of neutrophil cytosol factor 1 (Ncf1), neutrophilic inflammation driver lipocalin 2 (Lcn2), and complement component C5a receptor 1 (C5ar1), which are associated with neutrophilic inflammation. Interestingly, compared to PF+Pg mice, the livers of AF+Pg mice exhibited downregulation of gene expression levels of NADPH oxidase 2 (Cybb), the leukocyte adhesion molecule Cd18, and the Toll-like receptor adaptor Myd88. Consequently, impaired clearance of P. gingivalis and other bacteria in the liver, increased susceptibility to infections, and inflammation-associated hepatic necrotic cell death were observed in AF+Pg mice, which is likely to have facilitated immune cell infiltration and contributed to liver injury. Furthermore, in addition to the Srebf1/Fasn pathway induced by alcohol feeding, Pg infection also activated carbohydrate response element-binding protein (ChREBP) in AF+Pg mice. In summary, this study demonstrates that P. gingivalis infection, acting as a “second hit”, induces dysfunction of immune response and impairs the clearance of bacteria and infections in alcohol-sensitized livers. This process drives the development of liver injury.

Complement Activation in Nephrotic Glomerular Diseases

The nephrotic syndrome holds significant clinical importance and is characterized by a substantial protein loss in the urine. Damage to the glomerular basement membrane or podocytes frequently underlies renal protein loss. There is an increasing belief in the involvement of the complement system, a part of the innate immune system, in these conditions. Understanding the interactions between the complement system and glomerular structures continually evolves, challenging the traditional view of the blood-urine barrier as a passive filter. Clinical studies suggest that a precise inhibition of the complement system at various points may soon become feasible. However, a thorough understanding of current knowledge is imperative for planning future therapies in nephrotic glomerular diseases such as membranous glomerulopathy, membranoproliferative glomerulonephritis, lupus nephritis, focal segmental glomerulosclerosis, and minimal change disease. This review provides an overview of the complement system, its interactions with glomerular structures, and insights into specific glomerular diseases exhibiting a nephrotic course. Additionally, we explore new diagnostic tools and future therapeutic approaches.

Activation of the alternative complement pathway modulates inflammation in thoracic aortic aneurysm/dissection

Thoracic aortic aneurysm/dissection (TAAD) is a lethal vascular disease, and several pathological factors participate in aortic medial degeneration. We previously discovered that the complement C3a-C3aR axis in smooth muscle cells promotes the development of thoracic aortic dissection (TAD) through regulation of matrix metalloproteinase 2. However, discerning the specific complement pathway that is activated and elucidating how inflammation of the aortic wall is initiated remain unknown. We ascertained that the plasma levels of C3a and C5a were significantly elevated in patients with TAD and that the levels of C3a, C4a, and C5a were higher in acute TAD than in chronic TAD. We also confirmed the activation of the complement in a TAD mouse model. Subsequently, knocking out Cfb (Cfb) or C4 in mice with TAD revealed that the alternative pathway and Cfb played a significant role in the TAD process. Activation of the alternative pathway led to generation of the anaphylatoxins C3a and C5a, and knocking out their receptors reduced the recruitment of inflammatory cells to the aortic wall. Moreover, we used serum from wild-type mice or recombinant mice Cfb as an exogenous source of Cfb to treat Cfb KO mice and observed that it exacerbated the onset and rupture of TAD. Finally, we knocked out Cfb in the FBN1C1041G/+ Marfan-syndrome mice and showed that the occurrence of TAA was reduced. In summary, the alternative complement pathway promoted the development of TAAD by recruiting infiltrating inflammatory cells. Targeting the alternative pathway may thus constitute a strategy for preventing the development of TAAD.NEW & NOTEWORTHY The alternative complement pathway promoted the development of TAAD by recruiting infiltrating inflammatory cells. Targeting the alternative pathway may thus constitute a strategy for preventing the development of TAAD.

The transplant rejection response involves neutrophil and macrophage adhesion-mediated trogocytosis and is regulated by NFATc3

The anti-foreign tissue (transplant rejection) response, mediated by the immune system, has been the biggest obstacle to successful organ transplantation. There are still many enigmas regarding this process and some aspects of the underlying mechanisms driving the immune response against foreign tissues remain poorly understood. Here, we found that a large number of neutrophils and macrophages were attached to the graft during skin transplantation. Furthermore, both types of cells could autonomously adhere to and damage neonatal rat cardiomyocyte mass (NRCM) in vitro. We have demonstrated that Complement C3 and the receptor CR3 participated in neutrophils/macrophages-mediated adhesion and damage this foreign tissue (NRCM or skin grafts). We have provided direct evidence that the damage to these tissues occurs by a process referred to as trogocytosis, a damage mode that has never previously been reported to directly destroy grafts. We further demonstrated that this process can be regulated by NFAT, in particular, NFATc3. This study not only enriches an understanding of host-donor interaction in transplant rejection, but also provides new avenues for exploring the development of novel immunosuppressive drugs which prevent rejection during transplant therapy.

Clearance of apoptotic cells by neutrophils in inflammation and cancer

When a cell dies of apoptosis, it is eliminated either by neighbouring cells or by attracted professional phagocytes. Although it was generally believed that neutrophils also have the ability to perform efferocytosis, their contribution to the clearance of apoptotic cells was considered less important compared with macrophages. Therefore, this ability of neutrophils remained unexplored for a long time. Over the past decade, it has been shown that during inflammation, neutrophils contribute significantly to the clearance of apoptotic neutrophils that accumulate in large numbers at the site of tissue damage. This "neutrophil cannibalism" is accompanied by inhibition of pro-inflammatory activities of these cells, such as respiratory burst and formation of neutrophil extracellular traps (NETs). Furthermore, efferocytosing neutrophils secrete anti-inflammatory mediators and mitogens including hepatocyte growth factor (HGF), fibroblast growth factor 2 (FGF2), vascular endothelial growth factors (VEGF), and transforming growth factor beta (TGFβ). Thus, efferocytosis by neutrophils is involved in resolution of inflammation. Recent research indicates that it plays also a role in cancer. Many different solid tumours contain aggregates of dead tumour cells that have undergone spontaneous apoptosis. Their extent correlates with poor clinical outcome in most cancer types. These clusters of apoptotic tumour cells are strongly infiltrated by tumour-associated neutrophils (TANs) that acquired an anti-inflammatory and pro-resolving polarization state. This review summarizes the potential consequences discussed in the current literature. Although the picture of the role of efferocytosis by neutrophils in inflammation and cancer is becoming clearer, many questions are still unexplored.

The role and mechanism of action of microbiota-derived short-chain fatty acids in neutrophils: From the activation to becoming potential biomarkers

Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, have emerged as critical mediators in the communication between the human microbiota and its host. As the first responder to the inflammatory site, neutrophils play an important role in protecting the host against bacterial infections. Recent investigations revealed that SCFAs generated from microbiota influence various neutrophil activities, including activation, migration, and generation of mediators of inflammatory processes. SCFAs have also been demonstrated to exhibit potential therapeutic benefits in a variety of disorders related to neutrophil dysfunction, including inflammatory bowel disease, viral infectious disorders, and cancer. This study aims to examine the molecular processes behind the complicated link between SCFAs and neutrophils, as well as their influence on neutrophil-driven inflammatory disorders. In addition, we will also provide an in-depth review of current research on the diagnostic and therapeutic value of SCFAs as possible biomarkers for neutrophil-related diseases.

Anaphylatoxin signaling activates macrophages to control intracellular Rickettsia proliferation

IMPORTANCE

Pathogenic Rickettsia species are extremely dangerous bacteria that grow within the cytoplasm of host mammalian cells. In most cases, these bacteria are able to overpower the host cell and grow within the protected environment of the cytoplasm. However, a dramatic conflict occurs when Rickettsia encounter innate immune cells; the bacteria can "win" by taking over the host, or the bacteria can "lose" if the host cell efficiently fights the infection. This manuscript examines how the immune complement system is able to detect the presence of Rickettsia and alert nearby cells. Byproducts of complement activation called anaphylatoxins are signals that "activate" innate immune cells to mount an aggressive defensive strategy. This study enhances our collective understanding of the innate immune reaction to intracellular bacteria and will contribute to future efforts at controlling these dangerous infections.

The role of complement in kidney disease

The complement cascade comprises soluble and cell surface proteins and is an important arm of the innate immune system. Once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammatory, vasoactive and metabolic responses. Although complement is crucial to host defence and homeostasis, its inappropriate or uncontrolled activation can also drive tissue injury. For example, the complement system has been known for more than 50 years to be activated by glomerular immune complexes and to contribute to autoimmune kidney disease. Notably, the latest research shows that complement is also activated in kidney diseases that are not traditionally thought of as immune-mediated, including haemolytic-uraemic syndrome, diabetic kidney disease and focal segmental glomerulosclerosis. Several complement-targeted drugs have been approved for the treatment of kidney disease, and additional anti-complement agents are being investigated in clinical trials. These drugs are categorically different from other immunosuppressive agents and target pathological processes that are not effectively inhibited by other classes of immunosuppressants. The development of these new drugs might therefore have considerable benefits in the treatment of kidney disease.

Complement C1q essential for aeroallergen sensitization via CSF1R+ conventional dendritic cells type 2

BACKGROUND

Dendritic cells (DCs) are heterogeneous, comprising multiple subsets with unique functional specifications. Our previous work has demonstrated that the specific conventional type 2 DC subset, CSF1R+cDC2s, plays a critical role in sensing aeroallergens.

OBJECTIVE

It remains to be understood how CSF1R+cDC2s recognize inhaled allergens. We sought to elucidate the transcriptomic programs and receptor-ligand interactions essential for function of this subset in allergen sensitization.

METHODS

We applied single-cell RNA sequencing to mouse lung DCs. Conventional DC-selective knockout mouse models were employed, and mice were subjected to inhaled allergen sensitization with multiple readouts of asthma pathology. Under the clinical arm of this work, human lung transcriptomic data were integrated with mouse data, and bronchoalveolar lavage (BAL) specimens were collected from subjects undergoing allergen provocation, with samples assayed for C1q.

RESULTS

We found that C1q is selectively enriched in lung CSF1R+cDC2s, but not in other lung cDC2 or cDC1 subsets. Depletion of C1q in conventional DCs significantly attenuates allergen sensing and features of asthma. Additionally, we found that C1q binds directly to human dust mite allergen, and the C1q receptor CD91 (LRP1) is required for lung CSF1R+cDC2s to recognize the C1q-allergen complex and induce allergic lung inflammation. Lastly, C1q is enriched in human BAL samples following subsegmental allergen challenge, and human RNA sequencing data demonstrate close homology between lung IGSF21+DCs and mouse CSF1R+cDC2s.

CONCLUSIONS

C1q is secreted from the CSF1R+cDC2 subset among conventional DCs. Our data indicate that the C1q-LRP1 axis represents a candidate for translational therapeutics in the prevention and suppression of allergic lung inflammation.

Antibody-mediated phagocytosis in cancer immunotherapy

Unconjugated monoclonal antibodies (mAb) have revolutionized the treatment of many types of cancer. Some of these mAbs promote the clearance of malignant cells via direct cytotoxic effects. More recently, antibody-dependent cellular phagocytosis (ADCP) has been appreciated as a major mechanism of action for a number of widely-used mAbs, including anti-CD20 (rituximab, obinutuzumab), anti-HER2 (trazituzumab), and anti-CD38 (daratumumab). However, as a monotherapy these ADCP-inducing mAbs produce insufficient levels of cytotoxicity in vivo and are not curative. As a result, these mAbs are most effectively used in combination therapies. The efficacy of these mAbs is further hampered by the apparent development of drug resistance by many patients. Here we will explore the role of ADCP in cancer immunotherapy and discuss the key factors that could limit the efficacy of ADCP-inducing mAbs in vivo. Finally, we will discuss current insights and approaches being applied to overcome these limitations.

Structural biology of complement receptors

The complement system plays crucial roles in a wide breadth of immune and inflammatory processes and is frequently cited as an etiological or aggravating factor in many human diseases, from asthma to cancer. Complement receptors encompass at least eight proteins from four structural classes, orchestrating complement-mediated humoral and cellular effector responses and coordinating the complex cross-talk between innate and adaptive immunity. The progressive increase in understanding of the structural features of the main complement factors, activated proteolytic fragments, and their assemblies have spurred a renewed interest in deciphering their receptor complexes. In this review, we describe what is currently known about the structural biology of the complement receptors and their complexes with natural agonists and pharmacological antagonists. We highlight the fundamental concepts and the gray areas where issues and problems have been identified, including current research gaps. We seek to offer guidance into the structural biology of the complement system as structural information underlies fundamental and therapeutic research endeavors. Finally, we also indicate what we believe are potential developments in the field.