Classical complement pathway factor alterations in narcolepsy

Objective: Narcolepsy is a chronic sleep disorder long hypothesised to be an autoimmune disease. Complement-mediated immune mechanisms have not been investigated in detail in narcolepsy. Our aim was to establish the significance of classical pathway activation in narcolepsy. Methods: Sera of 42 narcolepsy patients and 26 healthy controls were screened with ELISA to determine the levels of C1q, C3a, C4d and complement component 4 binding protein (C4BP). A home-made ELISA method was developed to detect antibodies to C4BP-alpha (anti-C4BPA). The correlation between complement levels and clinical findings was examined. Results: C1q levels were significantly higher in narcolepsy patients while C4d and C4BP levels were significantly lower compared to healthy controls. C3a levels were comparable among patients and controls. Eleven narcolepsy patients showed serum anti-C4BPA levels. Total rapid eye movements (REM) time, sleep onset latency, REM sleep latency, sleep activity, percentage of wakefulness after sleep onset and Epworth sleepiness scale scores were correlated with levels of different complement factors. Conclusion: Complement-mediated immune mechanisms might partake in narcolepsy pathogenesis. The precise role of autoantibodies on complement level alterations needs to be investigated. Levels of complement factors and degradation products may potentially be utilised as biomarkers to predict the clinical severity of narcolepsy.

Complement cascade inhibition in geographic atrophy: a review

The pathophysiology of dry age-related macular degeneration (AMD) and specifically geographic atrophy (GA) has been linked to the complement cascade. This cascade is part of the innate immune system and is made up of the classical, alternative, and lectin pathways. The pathways comprise a system of plasma and membrane-associated serum proteins that are activated with identification of a nonself entity. A number of these proteins have been implicated in the development and progression of dry AMD. The three pathways converge at C3 and cascade down through C5, making both of these proteins viable targets for the treatment of dry AMD. In addition, there are a number of complement factors, CFB, CFD, CFH, and CFI, which are potential therapeutic targets as well. Several different complement-directed therapeutics are being studied for the treatment of dry AMD with the hope that one of these approaches will emerge as the first approved treatment for GA.

C4d Deposition after Allogeneic Renal Transplantation in Rats Is Involved in Initial Apoptotic Cell Clearance

In the context of transplantation, complement activation is associated with poor prognosis and outcome. While complement activation in antibody-mediated rejection is well-known, less is known about complement activation in acute T cell-mediated rejection (TCMR). There is increasing evidence that complement contributes to the clearance of apoptotic debris and tissue repair. In this regard, we have analysed published human kidney biopsy transcriptome data clearly showing upregulated expression of complement factors in TCMR. To clarify whether and how the complement system is activated early during acute TCMR, experimental syngeneic and allogeneic renal transplantations were performed. Using an allogeneic rat renal transplant model, we also observed upregulation of complement factors in TCMR in contrast to healthy kidneys and isograft controls. While staining for C4d was positive, staining with a C3d antibody showed no C3d deposition. FACS analysis of blood showed the absence of alloantibodies that could have explained the C4d deposition. Gene expression pathway analysis showed upregulation of pro-apoptotic factors in TCMR, and apoptotic endothelial cells were detected by ultrastructural analysis. Monocytes/macrophages were found to bind to and phagocytise these apoptotic cells. Therefore, we conclude that early C4d deposition in TCMR may be relevant to the clearance of apoptotic cells.

A Challenging Case of Atypical Hemolytic Uremic Syndrome in a Young African American Patient

Background It is known that malignant hypertension (mHTN) and thrombotic microangiopathy (TMA) commonly coexist. Deciding which phenomenon preceded the other remains a clinical dilemma, specifically in African American patients. However, making that determination is of utmost importance because the management will be different, and that can have dramatic effects on prognosis and outcomes. Herein, we report a case of atypical hemolytic uremic syndrome (aHUS) presenting as mHTN. Case Presentation A 35-year-old African American male with known history of hypertension, presented with nausea, vomiting, and diarrhea for four days. He also reported fatigue and exertional shortness of breath. Upon presentation, his blood pressure was 260/160 mmHg, otherwise physical exam was unremarkable. Initial work up showed hemoglobin of 8.8 g/dL (baseline 13.5), platelet count of 21,000/mL (baseline 250,000), serum creatinine of 16.99 mg/dL (baseline 0.99), MCV (84 fl), increased reticulocyte production index (3.58), increased LDH (1709 U/L), undetectable haptoglobin, and numerous schistocytes on peripheral blood smear. He was admitted as a case of hypertensive emergency and TMA. IV labetalol and hemodialysis were started. Given his gastrointestinal symptoms; stool for Shigella and E.Coli O157:H7 were checked and they were negative. Given the severity of his hematologic derangements and difficult to control blood pressure, we decided to proceed with renal biopsy to rule out primary aHUS which showed thrombotic microangiopathy, global glomerulosclerosis, moderate interstitial fibrosis and tubular atrophy suggestive of aHUS or rheumatologic disorders like systemic sclerosis and arguing against malignant HTN as the sole player. ANA and anti-Scl-70 antibodies were negative. Final impression was aHUS by exclusion, and patient received meningococcal vaccines (Menactra and Bexsero) in preparation to start eculizumab. aHUS genetic panel was sent which came back equivocal as it showed mutations of unknown significance (homozygous missense mutation in the MASP2 gene and 2 heterozygous mutations in the C2 gene). He was started on eculizumab 900 mg weekly for 4 weeks then 1200 mg biweekly starting week 5. He was seen in the office 2 months after initial presentation and receiving 5 doses of Eculizumab. His kidney function showed improvement with > 2 liters of urine output daily, blood pressure was better controlled. A decision by nephrology was made to give him a break from dialysis and remains dialysis-free a year later. Discussion aHUS is a rare disorder with an estimated prevalence of seven per one million children in Europe. It causes uninhibited activation of complement factors that leads to renal endothelial damage and activation of coagulation cascade leading to TMA. The diagnosis of aHUS requires the fulfillment of the classical triad (microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure) with a positive gene mutation or antibodies to complement factors. However, absence of these mutations or antibodies, as in the presented case, do not exclude the diagnosis. The early diagnosis of aHUS is necessary for treatment with eculizumab, a monoclonal antibody against C5 to block the terminal complement cascade. Kidney biopsy can be helpful in equivocal cases especially if it shows only the typical changes of malignant hypertension which essentially rules out aHUS. Hypertension with concurrent TMA is treated with strict BP control which is often enough to resolve TMA features and restores renal function, at least partially. On the contrary, aHUS causing severe HTN needs more sophisticated testing and blockade of the terminal complement component to improve outcome; that's why the distinction of which one is the primary process is of utmost importance. Our case emphasizes the importance of having low threshold for testing for aHUS in patients with mHTN and TMA, especially in African American patients where malignant HTN is known to happen more commonly, and to notice the subtle hints that may help in this distinction, such as profound hemolysis or thrombocytopenia out of proportion to what one would expect from mHTN alone. Early recognition of aHUS may save a patient's kidney. Disclosures No relevant conflicts of interest to declare.

Thermal Pain Thresholds Are Significantly Associated with Plasma Proteins of the Immune System in Chronic Widespread Pain—An Exploratory Pilot Study Using Multivariate and Network Analyses

Chronic widespread pain (CWP), including fibromyalgia (FM), is characterized by generalized musculoskeletal pain. An important clinical feature is widespread increased pain sensitivity such as lowered pain thresholds for different stimuli such as heat (HPT) and cold (CPT). There is a growing interest in investigating the activated neurobiological mechanisms in CWP. This explorative proteomic study investigates the multivariate correlation pattern between plasma and muscle proteins and thermal pain thresholds in CWP and in healthy controls (CON). In addition, we analysed whether the important proteins and their networks for CPT and HPT differed between CWP and CON. We used a proteomic approach and analysed plasma and muscle proteins from women with CWP (n = 15) and CON (n = 23). The associations between the proteins and CPT/HPT were analysed using orthogonal partial least square (OPLS). The protein–protein association networks for the important proteins for the two thermal pain thresholds were analysed using STRING database. CWP had lowered pain thresholds for thermal stimulus. These levels were generally not related to the included clinical variables except in CWP for HPT. Highly interacting proteins mainly from plasma showed strong significant associations with CPT and HPT both in CWP and in CON. Marked differences in the important proteins for the two thermal pain thresholds were noted between CWP and CON; more complex patterns emerged in CWP. The important proteins were part of the immune system (acute phase proteins, complement factors, and immunoglobulin factors) or known to interact with the immune system. As expected, CWP had lowered pain thresholds for thermal stimulus. Although different proteins were important in the two groups, there were similarities. For example, proteins related to the host defence/immunity such as acute phase proteins, complement factors, immunoglobulin factors, and cytokines/chemokines (although not in CON for CPT) were important habitual/tonic factors for thermal pain thresholds. The fact that peripheral proteins contribute to thermal pain thresholds does not exclude that central factors also contribute and that complex interactions between peripheral and central factors determine the registered pain thresholds in CWP.

The Role of Coagulation and Complement Factors for Mast Cell Activation in the Pathogenesis of Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is a common skin disorder characterized by an almost daily recurrence of wheal and flare with itch for more than 6 weeks, in association with the release of stored inflammatory mediators, such as histamine, from skin mast cells and/or peripheral basophils. The involvement of the extrinsic coagulation cascade triggered by tissue factor (TF) and complement factors, such as C3a and C5a, has been implied in the pathogenesis of CSU. However, it has been unclear how the TF-triggered coagulation pathway and complement factors induce the activation of skin mast cells and peripheral basophils in patients with CSU. In this review, we focus on the role of vascular endothelial cells, leukocytes, extrinsic coagulation factors and complement components on TF-induced activation of skin mast cells and peripheral basophils followed by the edema formation clinically recognized as urticaria. These findings suggest that medications targeting activated coagulation factors and/or complement components may represent new and effective treatments for patients with severe and refractory CSU.

Host-Specific Serum Factors Control the Development and Survival of Schistosoma mansoni

IntroductionSchistosomiasis is a neglected tropical disease (NTD) caused by blood-dwelling flatworms which develop from skin-penetrating cercariae, the freely swimming water-borne infective stage of Schistosoma mansoni, into adult worms. This natural course of infection can be mimicked in experimental mouse models of schistosomiasis. However, only a maximum of 20-30% of penetrated cercariae mature into fecund adults. The reasons for this are unknown but could potentially involve soluble factors of the innate immune system, such as complement factors and preexisting, natural antibodies.Materials and MethodsUsing our recently developed novel serum- and cell-free in vitro culture system for newly transformed schistosomula (NTS), which supports long-term larval survival, we investigated the effects of mouse serum and its major soluble complement factors C1q, C3, C4 as well as preexisting, natural IgM in vitro and assessed worm development in vivo by infecting complement and soluble (s)IgM-deficient animals.ResultsIn contrast to sera from humans and a broad variety of mammalian species, serum from mice, surprisingly, killed parasites already at skin stage in vitro. Interestingly, the most efficient killing component(s) were heat-labile but did not include important members of the perhaps best known family of heat-labile serum factors, the complement system, nor consisted of complement-activating natural immunoglobulins. Infection of complement C1q and sIgM-deficient mice with S. mansoni as well as in vitro tests with sera from mice deficient in C3 and C4 revealed no major role for these soluble factors in vivo in regard to parasite maturation, fecundity and associated immunopathology. Rather, the reduction of parasite maturation from cercariae to adult worms was comparable to wild-type mice.ConclusionThis study reveals that not yet identified heat-labile serum factors are major selective determinants of the host-specificity of schistosomiasis, by directly controlling schistosomal development and survival.

Increased Presence of Complement Factors and Mast Cells in Alveolar Bone and Tooth Resorption

Periodontitis is the inflammatory destruction of the tooth-surrounding and -supporting tissue, resulting at worst in tooth loss. Another locally aggressive disease of the oral cavity is tooth resorption (TR). This is associated with the destruction of the dental mineralized tissue. However, the underlying pathomechanisms remain unknown. The complement system, as well as mast cells (MCs), are known to be involved in osteoclastogenesis and bone loss. The complement factors C3 and C5 were previously identified as key players in periodontal disease. Therefore, we hypothesize that complement factors and MCs might play a role in alveolar bone and tooth resorption. To investigate this, we used the cat as a model because of the naturally occurring high prevalence of both these disorders in this species. Teeth, gingiva samples and serum were collected from domestic cats, which had an appointment for dental treatment under anesthesia, as well as from healthy cats. Histological analyses, immunohistochemical staining and the CH-50 and AH-50 assays revealed increased numbers of osteoclasts and MCs, as well as complement activity in cats with TR. Calcifications score in the gingiva was highest in animals that suffer from TR. This indicates that MCs and the complement system are involved in the destruction of the mineralized tissue in this condition.