Anaphylatoxins spark the flame in early autoimmunity

Th2 predominance and decreased NK cells in patients with hereditary angioedema

Background

In this study we included patients with hereditary angioedema (HAE) caused by decreased levels of C1 inhibitor (HAE-C1INH). An increased risk of autoimmune disorders, particularly systemic lupus erythematosus (SLE), has been reported in HAE-C1INH. This suggests that complement consumption affects adaptive immunity.

Objective

To investigate lymphocyte subpopulations in relation to disease activity and complement activation in HAE-C1INH patients and matched controls.

Methods

Flow cytometry of peripheral blood lymphocyte populations, measurements of complement and complement fragments, and collection of clinical data.

Results

NK cell counts were lower in HAE-C1INH patients, and their frequencies were related to disease activity. The T helper (Th) cell balance was skewed towards more Th2 cells and less Th1 cells in HAE-C1INH patients compared to controls. There were also lower frequencies of class-switched B cells and plasmablasts in patients. Levels of C4 and the complement activation fragment C3d were related to disease activity.

Conclusions

Blood lymphocyte populations are altered in HAE-C1INH, a finding which may be of pathophysiological importance considering the increased risks of both autoimmunity and allergy associated with HAE-C1INH.

Evolving understanding of Guillain-Barré syndrome pathophysiology and the central role of the classical complement pathway in axonal injury

Guillain-Barré syndrome (GBS) is a rare, frequently postinfectious neuromuscular emergency and the leading cause of acute paralytic neuropathy worldwide. GBS incidence varies considerably across geographic regions, owing predominantly to different infectious exposures. In GBS, antecedent infection leads to production of immunoglobulin G and immunoglobulin M antibodies that cross-react with the myelin sheath and axons of peripheral nerves. These antibodies activate the classical complement pathway, which plays a key role in peripheral nerve injury regardless of autoantibody binding to myelin or axons as a target. The heterogeneous clinical presentation and progression of GBS symptoms have long been attributed to binary axonal and demyelinating neurophysiologic classifications; however, evolving evidence indicates that these pathophysiologic processes overlap. Intravenous immunoglobulin and plasma exchange, the current standard-of-care therapies in GBS, both reduce autoantibody levels and complement activation, thereby aiming to address this convergence of pathophysiology. However, these therapies only partially decrease antibody levels and complement activity and require extended courses of treatment (5 days for intravenous immunoglobulin and 7-14 days for plasma exchange), limiting their effectiveness in addressing acute neuronal damage during the active phase of disease. Given its evolutionary role in antibody binding and activating the classical complement pathway, the complement component C1q has been proposed as a therapeutic target in GBS. The clinical trial program of the C1q inhibitor ANX005, including placebo-controlled, double-blind phase 1b and phase 3 trials in GBS, provides insight into the pathophysiology of GBS and the efficacy of C1q inhibition regardless of neurophysiologic classification or geographic location.

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.

Expanded Spectrum and Increased Incidence of Adverse Events Linked to COVID-19 Genetic Vaccines: New Concepts on Prophylactic Immuno-Gene Therapy, Iatrogenic Orphan Disease, and Platform-Inherent Challenges

The mRNA- and DNA-based "genetic" COVID-19 vaccines can induce a broad range of adverse events (AEs), with statistics showing significant variation depending on the timing and data analysis methods used. Focusing only on lipid nanoparticle-enclosed mRNA (mRNA-LNP) vaccines, this review traces the evolution of statistical conclusions on the prevalence of AEs and incidents associated with these vaccines, from initial underestimation of atypical, severe toxicities to recent claims suggesting the possible contribution of COVID-19 vaccinations to the excess deaths observed in many countries over the past few years. Among hundreds of different AEs listed in Pfizer's pharmacovigilance survey, the present analysis categorizes the main symptoms according to organ systems, with nearly all of them being affected. Using data from the US Vaccine Adverse Event Reporting System and a global vaccination dataset, a comparison of the prevalence and incidence rates of AEs induced by genetic versus flu vaccines revealed an average 26-fold increase in AEs with the use of genetic vaccines. The difference is especially pronounced in the case of severe 'Brighton-listed' AEs, which are also observed in COVID-19 and post-COVID conditions. Among these, the increases in incidence rates relative to flu vaccines, given as x-fold rises, were 1152x, 455x, 226x, 218x, 162x, 152x, and 131x for myocarditis, thrombosis, death, myocardial infarction, tachycardia, dyspnea, and hypertension, respectively. The review delineates the concept that genetic vaccines can be regarded as prophylactic immuno-gene therapies and that the observed chronic disabling AEs might be categorized as iatrogenic orphan diseases. It also examines the unique vaccine characteristics that could be causally related to abnormal immune responses which potentially lead to adverse events and complications. These new insights may contribute to improving the safety of this platform technology and assessing the risk/benefit balance of various products.

NHERF2 regulatory function in signal transduction pathways and control of gene expression: Implications for cellular homeostasis and breast cancer

Na⁺/H⁺ exchanger regulatory factor 2 (NHERF2) is a nucleocytoplasmic protein initially identified as a regulator of membrane-bound sodium-hydrogen exchanger 3 (NHE3). In the cytoplasm, NHERF2 regulates the activity of G protein-coupled receptors (GPCRs), including beta-2 adrenergic receptor (2β-AR), lysophosphatidic acid receptor 2, and parathyroid hormone type 1 receptor. In the nucleus, NHERF2 acts as a coregulator of transcription factors such as sex-determining region Y protein (SRY), involved in male sex determination, and estrogen receptor alpha (ERα). ERα is a ligand-dependent transcription factor that controls mammary gland growth and differentiation during puberty and pregnancy and plays a major role in the development and progression of breast cancer tumors. Altogether, the regulatory functions of NHERF2 on ion channels, GPCRs, and nuclear transcription factors have a modulatory effect on signal transduction pathways, metabolic homeostasis, cell proliferation and differentiation, neurotransmission, muscle contraction, and renal electrolyte balance. This work highlights NHERF2 functions in the cytoplasm and nucleus and underscores the nuclear mechanisms through which NHERF2 participates in the regulation of gene expression and tumor growth and progression in breast cancer.

Immunopathogenesis of systemic lupus erythematosus: An update

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disease characterized by dysregulated immune responses leading to widespread inflammation and damage in various organs. Environmental factors such as infections, hormonal influences and exposure to ultraviolet light can trigger the disease in genetically predisposed individuals. Genome-wide association studies have identified over 100 susceptibility loci linked to immune regulation, interferon (IFN) signaling and antigen presentation in SLE. In addition, rare cases of monogenic lupus have been instrumental in understanding critical underlying disease mechanisms. Several immunological abnormalities contribute to the loss of self-tolerance and the perpetuation of autoimmune responses in SLE. In particular, defective clearance of apoptotic cells due to defective phagocytosis and complement activation leads to accumulation of self-antigens. Dysregulated innate immune responses activate the adaptive immune system, amplifying the inflammatory response with an important role for type I IFNs. Abnormalities in B cell development and activation lead to the production of autoreactive antibodies, forming immune complexes that cause tissue damage. Similarly, disturbances in T-cell compartments, altered regulatory T-cell functions and altered cytokine production, particularly IFN-α, contribute to tissue damage. Understanding of the immunopathogenesis of SLE is evolving rapidly, with ongoing research identifying new molecular pathways and potential therapeutic targets. Future classifications of SLE are likely to be based on underlying biological pathways rather than clinical and serological signs alone. This review aims to provide a detailed update on the most recent findings regarding the immunopathogenesis of SLE, focusing on the variability of biological pathways and the implications for future therapeutic strategies, in particular chimeric antigen receptor T (CAR T) cells.

Structural analysis of the human C5a-C5aR1 complex using cryo-electron microscopy

The complement system is a complex network of proteins that plays a crucial role in the innate immune response. One important component of this system is the C5a-C5aR1 complex, which is critical in the recruitment and activation of immune cells. In-depth investigation of the activation mechanism as well as biased signaling of the C5a-C5aR1 system will facilitate the elucidation of C5a-mediated pathophysiology. In this study, we determined the structure of C5a-C5aR1-Gi complex at a high resolution of 3 Å using cryo-electron microscopy (Cryo-EM). Our results revealed the binding site of C5a, which consists of a polar recognition region on the extracellular side and an amphipathic pocket within the transmembrane domain. Furthermore, we found that C5a binding induces conformational changes of C5aR1, which subsequently leads to the activation of G protein signaling pathways. Notably, a key residue (M265) located on transmembrane helix 6 (TM6) was identified to play a crucial role in regulating the recruitment of β-arrestin driven by C5a. This study provides more information about the structure and function of the human C5a-C5aR1 complex, which is essential for the proper functioning of the complement system. The findings of this study can also provide a foundation for the design of new pharmaceuticals targeting this receptor with bias or specificity.

sMR and PTX3 levels associate with COVID-19 outcome and survival but not with Long COVID

Biomarkers for monitoring COVID-19 disease course are lacking. Study aim was to identify biomarkers associated with disease severity, survival, long-term outcome, and Long COVID. As excessive macrophages activation is a hallmark of COVID-19 and complement activation is key in this, we selected the following proteins involved in these processes: PTX3, C1q, C1-INH, C1s/C1-INH, and sMR. EDTA-plasma concentrations were measured in 215 patients and 47 controls using ELISA. PTX3, sMR, C1-INH, and C1s/C1-INH levels were associated with disease severity. PTX3 and sMR were also associated with survival and long-term immune recovery. Lastly, sMR levels associate with ICU admittance. sMR (AUC 0.85) and PTX3 (AUC 0.78) are good markers for disease severity, especially when used in combination (AUC 0.88). No association between biomarker levels and Long COVID was observed. sMR has not previously been associated with COVID-19 disease severity, ICU admittance or survival and may serve as marker for disease course.

Association of Complement Factors With Disability Progression in Primary Progressive Multiple Sclerosis

BACKGROUND AND OBJECTIVES

The complement system is known to play a role in multiple sclerosis (MS) pathogenesis. However, its contribution to disease progression remains elusive. The study investigated the role of the complement system in disability progression of patients with primary progressive MS (PPMS).

METHODS

Sixty-eight patients with PPMS from 12 European MS centers were included in the study. Serum and CSF levels of a panel of complement components (CCs) were measured by multiplex enzyme-linked immunosorbent assay at a baseline time point (i.e., sampling). Mean (SD) follow-up time from baseline was 9.6 (4.8) years. Only one patient (1.5%) was treated during follow-up. Univariable and multivariable logistic regressions adjusted for age, sex, and albumin quotient were performed to assess the association between baseline CC levels and disability progression in short term (2 years), medium term (6 years), and long term (at the time of the last follow-up).

RESULTS

In short term, CC played little or no role in disability progression. In medium term, an elevated serum C3a/C3 ratio was associated with a higher risk of disability progression (adjusted OR 2.30; 95% CI 1.17-6.03; p = 0.040). By contrast, increased CSF C1q levels were associated with a trend toward reduced risk of disability progression (adjusted OR 0.43; 95% CI 0.17-0.98; p = 0.054). Similarly, in long term, an elevated serum C3a/C3 ratio was associated with higher risk of disability progression (adjusted OR 1.81; 95% CI 1.09-3.40; p = 0.037), and increased CSF C1q levels predicted lower disability progression (adjusted OR 0.41; 95% CI 0.17-0.86; p = 0.025).

DISCUSSION

Proteins involved in the activation of early complement cascades play a role in disability progression as risk (elevated serum C3a/C3 ratio) or protective (elevated CSF C1q) factors after 6 or more years of follow-up in patients with PPMS. The protective effects associated with C1q levels in CSF may be related to its neuroprotective and anti-inflammatory properties.

The role of the complement system in disc degeneration and Modic changes

Disc degeneration and vertebral endplate bone marrow lesions called Modic changes are prevalent spinal pathologies found in chronic low back pain patients. Their pathomechanisms are complex and not fully understood. Recent studies have revealed that complement system proteins and interactors are dysregulated in disc degeneration and Modic changes. The complement system is part of the innate immune system and plays a critical role in tissue homeostasis. However, its dysregulation has also been associated with various pathological conditions such as rheumatoid arthritis and osteoarthritis. Here, we review the evidence for the involvement of the complement system in intervertebral disc degeneration and Modic changes. We found that only a handful of studies reported on complement factors in Modic changes and disc degeneration. Therefore, the level of evidence for the involvement of the complement system is currently low. Nevertheless, the complement system is tightly intertwined with processes known to occur during disc degeneration and Modic changes, such as increased cell death, autoantibody production, bacterial defense processes, neutrophil activation, and osteoclast formation, indicating a contribution of the complement system to these spinal pathologies. Based on these mechanisms, we propose a model how the complement system could contribute to the vicious cycle of tissue damage and chronic inflammation in disc degeneration and Modic changes. With this review, we aim to highlight a currently understudied but potentially important inflammatory pathomechanism of disc degeneration and Modic changes that may be a novel therapeutic target.

Decrease in multiple complement proteins associated with development of islet autoimmunity and type 1 diabetes

Type 1 diabetes (T1D) is a chronic condition caused by autoimmune destruction of the insulin-producing pancreatic β cells. While it is known that gene-environment interactions play a key role in triggering the autoimmune process leading to T1D, the pathogenic mechanism leading to the appearance of islet autoantibodies-biomarkers of autoimmunity-is poorly understood. Here we show that disruption of the complement system precedes the detection of islet autoantibodies and persists through disease onset. Our results suggest that children who exhibit islet autoimmunity and progress to clinical T1D have lower complement protein levels relative to those who do not progress within a similar time frame. Thus, the complement pathway, an understudied mechanistic and therapeutic target in T1D, merits increased attention for use as protein biomarkers of prediction and potentially prevention of T1D.

Pseudo-allergic reactions induced by Chinese medicine injections: a review

Traditional Chinese medicine injections (TCMIs) is a new dosage form of Chinese medicine, which plays a unique role in rescuing patients with critical illnesses that are difficult to replace. With the rapid development and widespread application of TCMIs in recent years, their adverse events have emerged and attracted much attention. Among them, pseudo-allergic reactions, i.e., the most significant adverse reactions occurring with the first dose without immunoglobulin E mediated conditions. Currently, studies on the types of TCMIs and antibiotic mechanisms that cause pseudo-allergic reactions are incomplete, and standard models and technical guidelines for assessing TCMIs have not been established. First, this review describes the causes of pseudo-allergic reactions, in which the components and structures responsible for pseudo-allergic reactions are summarized. Second, the mechanisms by which pseudo-allergic reactions are discussed, including direct stimulation of mast cells and complement activation. Then, research models of pseudo-allergic reaction diseases are reviewed, including animal models and cellular models. Finally, the outlook and future challenges for the development of pseudo-allergic reactions in traditional Chinese medicine (TCM) are outlined. This shed new light on the assessment and risk prevention of pseudo-allergic reactions in TCM and the prevention of clinical adverse reactions in TCM.

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.

The role of C5a receptors in autoimmunity

The complement system is an essential component of the innate immune response and plays a vital role in host defense and inflammation. Dysregulation of the complement system, particularly involving the anaphylatoxin C5a and its receptors (C5aR1 and C5aR2), has been linked to several autoimmune diseases, indicating the potential for targeted therapies. C5aR1 and C5aR2 are seven-transmembrane receptors with distinct signaling mechanisms that play both partially overlapping and opposing roles in immunity. Both receptors are expressed on a broad spectrum of immune and non-immune cells and are involved in cellular functions and physiological processes during homeostasis and inflammation. Dysregulated C5a-mediated inflammation contributes to autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, epidermolysis bullosa acquisita, antiphospholipid syndrome, and others. Therefore, targeting C5a or its receptors may yield therapeutic innovations in these autoimmune diseases by reducing the recruitment and activation of immune cells that lead to tissue inflammation and injury, thereby exacerbating the autoimmune response. Clinical trials focused on the inhibition of C5 cleavage or the C5a/C5aR1-axis using small molecules or monoclonal antibodies hold promise for bringing novel treatments for autoimmune diseases into practice. However, given the heterogeneous nature of (systemic) autoimmune diseases, there are still several challenges, such as patient selection, optimal dosing, and treatment duration, that require further investigation and development to realize the full therapeutic potential of C5a receptor inhibition, ideally in the context of a personalized medicine approach. Here, we aim to provide a brief overview of the current knowledge on the function of C5a receptors, the involvement of C5a receptors in autoimmune disorders, the molecular mechanisms underlying C5a receptor-mediated autoimmunity, and the potential for targeted therapies to modulate their activity.

Mast Cells and Basophils in IgE-Independent Anaphylaxis

Anaphylaxis is a life-threatening or even fatal systemic hypersensitivity reaction. The incidence of anaphylaxis has risen at an alarming rate in the past decades in the majority of countries. Generally, the most common causes of severe or fatal anaphylaxis are medication, foods and Hymenoptera venoms. Anaphylactic reactions are characterized by the activation of mast cells and basophils and the release of mediators. These cells express a variety of receptors that enable them to respond to a wide range of stimulants. Most studies of anaphylaxis focus on IgE-dependent reactions. The mast cell has long been regarded as the main effector cell involved in IgE-mediated anaphylaxis. This paper reviews IgE-independent anaphylaxis, with special emphasis on mast cells, basophils, anaphylactic mediators, risk factors, triggers, and management.

The complement system and human autoimmune diseases

Genetic deficiencies of early components of the classical complement activation pathway (especially C1q, r, s, and C4) are the strongest monogenic causal factors for the prototypic autoimmune disease systemic lupus erythematosus (SLE), but their prevalence is extremely rare. In contrast, isotype genetic deficiency of C4A and acquired deficiency of C1q by autoantibodies are frequent among patients with SLE. Here we review the genetic basis of complement deficiencies in autoimmune disease, discuss the complex genetic diversity seen in complement C4 and its association with autoimmune disease, provide guidance as to when clinicians should suspect and test for complement deficiencies, and outline the current understanding of the mechanisms relating complement deficiencies to autoimmunity. We focus primarily on SLE, as the role of complement in SLE is well-established, but will also discuss other informative diseases such as inflammatory arthritis and myositis.

Autoimmune pre-disease

Approximately 5% of the world-wide population is affected by autoimmune diseases. Overall, autoimmune diseases are still difficult to treat, impose a high burden on patients, and have a significant economic impact. Like other complex diseases, e.g., cancer, autoimmune diseases develop over several years. Decisive steps in the development of autoimmune diseases are (i) the development of autoantigen-specific lymphocytes and (often) autoantibodies and (ii) potentially clinical disease manifestation at a later stage. However, not all healthy individuals with autoantibodies develop disease manifestations. Identifying autoantibody-positive healthy individuals and monitoring and inhibiting their switch to inflammatory autoimmune disease conditions are currently in their infancy. The switch from harmless to inflammatory autoantigen-specific T and B-cell and autoantibody responses seems to be the hallmark for the decisive factor in inflammatory autoimmune disease conditions. Accordingly, biomarkers allowing us to predict this progression would have a significant impact. Several factors, such as genetics and the environment, especially diet, smoking, exposure to pollutants, infections, stress, and shift work, might influence the progression from harmless to inflammatory autoimmune conditions. To inspire research directed at defining and ultimately targeting autoimmune predisease, here, we review published evidence underlying the progression from health to autoimmune predisease and ultimately to clinically manifest inflammatory autoimmune disease, addressing the following 3 questions: (i) what is the current status, (ii) what is missing, (iii) and what are the future perspectives for defining and modulating autoimmune predisease.