Importance of the Complement Alternative Pathway in Serum Chemotactic Activity During Sepsis

Immunotherapy in the context of sepsis-induced immunological dysregulation

Sepsis is a clinical syndrome caused by uncontrollable immune dysregulation triggered by pathogen infection, characterized by high incidence, mortality rates, and disease burden. Current treatments primarily focus on symptomatic relief, lacking specific therapeutic interventions. The core mechanism of sepsis is believed to be an imbalance in the host's immune response, characterized by early excessive inflammation followed by late immune suppression, triggered by pathogen invasion. This suggests that we can develop immunotherapeutic treatment strategies by targeting and modulating the components and immunological functions of the host's innate and adaptive immune systems. Therefore, this paper reviews the mechanisms of immune dysregulation in sepsis and, based on this foundation, discusses the current state of immunotherapy applications in sepsis animal models and clinical trials.

Cobra Venom Factor Boosts Arteriogenesis in Mice

Arteriogenesis, the growth of natural bypass blood vessels, can compensate for the loss of arteries caused by vascular occlusive diseases. Accordingly, it is a major goal to identify the drugs promoting this innate immune system-driven process in patients aiming to save their tissues and life. Here, we studied the impact of the Cobra venom factor (CVF), which is a C3-like complement-activating protein that induces depletion of the complement in the circulation in a murine hind limb model of arteriogenesis. Arteriogenesis was induced in C57BL/6J mice by femoral artery ligation (FAL). The administration of a single dose of CVF (12.5 µg) 24 h prior to FAL significantly enhanced the perfusion recovery 7 days after FAL, as shown by Laser Doppler imaging. Immunofluorescence analyses demonstrated an elevated number of proliferating (BrdU+) vascular cells, along with an increased luminal diameter of the grown collateral vessels. Flow cytometric analyses of the blood samples isolated 3 h after FAL revealed an elevated number of neutrophils and platelet-neutrophil aggregates. Giemsa stains displayed augmented mast cell recruitment and activation in the perivascular space of the growing collaterals 8 h after FAL. Seven days after FAL, we found more CD68+/MRC-1+ M2-like polarized pro-arteriogenic macrophages around growing collaterals. These data indicate that a single dose of CVF boosts arteriogenesis by catalyzing the innate immune reactions, relevant for collateral vessel growth.

Neutrophil extracellular trap formation index predicts occurrences of deep surgical site infection after laparotomy

Background

Deep surgical site infections (DSSIs) are serious complications after laparotomy. Neutrophil extracellular traps (NETs) play a vital role in the development of DSSI. Here, we focused on a new approach to predicting the occurrence of DSSI through the detection of the NET formation index (NFI), and compared its prediction ability with other clinical infection indicators.

Methods

Patients who received laparotomy were prospectively enrolled in this study. General information, APACHE II score, SOFA score, and serum infection indicators were recorded. The postoperative abdominal drainage fluid was collected within 3 days after the operation for quantification of the NFI.

Results

A total of 92 consecutive patients were included, with 22 patients were diagnosed with DSSI. The NFI in the DSSI group was 32.70%±19.33% while the corresponding index was 10.70%±8.25% in the non-DSSI group (P<0.01). The mean APACHE II and SOFA score had significant differences between the two groups. The NFI was positively correlated with the APACHE II score (P<0.01, r=0.269) and SOFA score (P=0.013, r=0.258). Patients with a high NFI (NFI >13.86%) had a higher risk of developing DSSI. According to the receiver operating characteristic (ROC) curve, the area under the ROC curve (AUC) of the NFI, C-reactive protein (CRP) and procalcitonin (PCT) were 0.912, 0.748 and 0.731, respectively.

Conclusions

In this cohort of surgical patients, the quantification of the NFI had a considerable predictive value for early identification of DSSI. The NFI in drainage fluid turned out to be a more sensitive and specific predictor of DSSI than serum infection indicators including CRP and PCT.

Drug delivery systems as immunomodulators for therapy of infectious disease: Relevance to COVID-19

The emergence of SARS-CoV-2, and the ensuing global pandemic, has resulted in an unprecedented response to identify therapies that can limit uncontrolled inflammation observed in patients with moderate to severe COVID-19. The immune pathology behind COVID-19 is complex and involves the activation and interaction of multiple systems including, but not limited to, complement, inflammasomes, endothelial as well as innate and adaptive immune cells to bring about a convoluted profile of inflammation, coagulation and tissue damage. To date, therapeutic approaches have focussed on inhibition of coagulation, untargeted immune suppression and/or cytokine-directed blocking agents. Regardless of recently achieved improvements in individual patient outcomes and survival rates, improved and focussed approaches targeting individual systems involved is needed to further improve prognosis and wellbeing. This review summarizes the current understanding of molecular and cellular systems involved in the pathophysiology of COVID-19, and their contribution to pathogen clearance and damage to then discuss possible therapeutic options involving immunomodulatory drug delivery systems as well as summarising the complex interplay between them.

Emerging roles of the complement system in host-pathogen interactions

The complement system has historically been entertained as a fluid-phase, hepatically derived system which protects the intravascular space from encapsulated bacteria. However, there has been an increasing appreciation for its role in protection against non-encapsulated pathogens. Specifically, we have an improved understanding of how pathogens are recognized by specific complement proteins, as well as how they trigger and evade them. Additionally, we have an improved understanding of locally derived complement proteins, many of which promote host defense. Moreover, intracellular complement proteins have been identified that facilitate local protection and barrier function despite pathogen invasion. Our review aims to summarize these advances in the field as well as provide an insight into the pathophysiological changes occurring when the system is dysregulated in infection.

Complement Activation in Human Sepsis is Related to Sepsis-Induced Disseminated Intravascular Coagulation

INTRODUCTION

In human sepsis, little is known about the relationships between complement activation and the clinical characteristics of sepsis, including disseminated intravascular coagulation (DIC), interventions, and prognosis.

PATIENTS AND METHODS

Adult patients with sepsis admitted from November 2016 to December 2018 were included. We used the plasma levels of soluble C5b-9 (SC5b-9) as a marker of complement activation. We compared the clinical characteristics and complement components between patients with and without DIC. We also compared the clinical characteristics and each DIC parameter across quartile groups for the SC5b-9 value.

RESULTS

Forty-nine sepsis patients were eligible. Thirty-four patients developed DIC, and eight patients died. The median (interquartile range) SC5b-9 value was 342 (261-501) ng/mL. Compared with patients without DIC, patients with DIC showed lower C3 levels (mean, 95.7 vs. 70.4 mg/dL, P < 0.01) and higher SC5b-9 levels (median, 287 vs. 400 ng/mL, P = 0.01). Patients were stratified by SC5b-9 quartile (ng/mL: low: < 260, moderate: 260-342, high: 343-501, highest: > 501). The mean Sequential Organ Failure Assessment score varied across these groups (P = 0.02). In the high and highest groups, many more patients received vasopressors and developed DIC. In the highest group, the coagulation parameters were severe, and thrombocytopenia was prolonged. In-hospital mortality tended to be high (33%) in the highest group.

CONCLUSIONS

The degree of complement activation is related to DIC, severity, intensive interventions, and mortality. Further studies are needed to confirm the usefulness of SC5b-9 for stratifying sepsis patients.

Complement as a Major Inducer of Harmful Events in Infectious Sepsis

There is abundant evidence that infectious sepsis both in humans and mice with polymicrobial sepsis results in robust activation of complement. Major complement activation products involved in sepsis include C5a anaphylatoxin and its receptors (C5aR1 and C5aR2) and, perhaps, the terminal complement activation product, C5b-9. These products (and others) also cause dysfunction of the innate immune system, with exaggerated early proinflammatory responses, followed by decline of the innate immune system, leading to immunosuppression and multiorgan dysfunction. Generation of C5a during sepsis also leads to activation of neutrophils and macrophages and ultimate appearance of extracellular histones, which have powerful proinflammatory and prothrombotic activities. The distal complement activation product, C5b-9, triggers intracellular Ca fluxes in epithelial and endothelial cells. Histones activate the NLRP3 inflammasome, products of which can damage cells. C5a also activates MAPKs and Akt signaling pathways in cardiomyocytes, causing buildup of [Ca]i, defective action potentials and substantial cell dysfunction, resulting in cardiac and other organ dysfunction. Cardiac dysfunction can be quantitated by ECHO-Doppler parameters. In vivo interventions that block these complement-dependent products responsible for organ dysfunction in sepsis reduce the intensity of sepsis. The obvious targets in sepsis are C5a and its receptors, histones, and perhaps the MAPK pathways. Blockade of C5 has been considered in sepsis, but the FDA-approved antibody (eculizumab) is known to compromise defenses against neisseria and pneumonococcal bacteria, and requires immunization before the mAb to C5 can be used clinically. Small molecular blocking agents for C5aRs are currently in development and may be therapeutically effective for treatment of sepsis.

Anaphylatoxins Enhance Recruitment of Nonclassical Monocytes via Chemokines Produced by Pleural Mesothelial Cells in Tuberculous Pleural Effusion

In the present study, we sought to elucidate the mechanisms by which monocytes migrate into the pleural space in the presence of anaphylatoxins in tuberculous pleural effusion (TPE). Monocytes in both pleural effusion and blood were counted, and their phenotypic characteristics were analyzed. Activation of the complement system was detected in TPE. The effects of Mpt64 and anaphylatoxins on the production of chemokines in pleural mesothelial cells (PMCs) were measured. The chemoattractant activity of chemokines produced by PMCs for monocytes was observed. Levels of CD14⁺CD16⁺ monocytes were significantly higher in TPE than in blood. Three pathways of the complement system were activated in TPE. C3a-C3aR1, C5a-C5aR1, CCL2-CCR2, CCL7-CCR2, and CX3CL1-CX3CR1 were coexpressed in PMCs and monocytes isolated from TPE. Moreover, we initially found that Mpt64 stimulated the expression of C3a and C5a in PMCs. C3a and C5a not only induced CCL2, CCL7, and CX3CL1 expression in PMCs but also stimulated production of IL-1β, IL-17, and IL-27 in monocytes. C3a and C5a stimulated PMCs to secrete CCL2, CCL7, and CX3CL1, which recruited CD14⁺CD16⁺ monocytes to the pleural cavity. As a result, the infiltration of CD14⁺CD16⁺ monocytes engaged in the pathogenesis of TPE by excessive production of inflammatory cytokines.

The Influence of Pain and Analgesia in Rodent Models of Sepsis

Sepsis is a multifaceted host response to infection that dramatically affects patient outcomes and the cost of health care. Animal models are necessary to replicate the complexity and heterogeneity of clinical sepsis. However, these models entail a high risk of pain and distress due to tissue trauma, inflammation, endotoxin-mediated hyperalgesia, and other mechanisms. Several recent studies and initiatives address the need to improve the welfare of animals through analgesics and standardize the models used in preclinical sepsis research. Ultimately, the goal is to provide high-fidelity, humane animal models that better replicate the clinical course of sepsis, to provide more effective translation and advance therapeutic discovery. The purpose of this review is to discuss the current understanding of the roles of pain and analgesia in rodent models of sepsis. The current definitions of sepsis along with an overview of pain in human sepsis are described. Finally, welfare concerns associated with animal models of sepsis and the most recent considerations for relief of pain and distress are reviewed.