Neurological Manifestations of COVID-19 Feature T Cell Exhaustion and Dedifferentiated Monocytes in Cerebrospinal Fluid.

Patients suffering from Coronavirus disease 2019 (COVID-19) can develop neurological sequelae, such as headache and neuroinflammatory or cerebrovascular disease. These conditions-termed here as Neuro-COVID-are more frequent in patients with severe COVID-19. To understand the etiology of these neurological sequelae, we utilized single-cell sequencing and examined the immune cell profiles from the cerebrospinal fluid (CSF) of Neuro-COVID patients compared with patients with non-inflammatory and autoimmune neurological diseases or with viral encephalitis. The CSF of Neuro-COVID patients exhibited an expansion of dedifferentiated monocytes and of exhausted CD4+ T cells. Neuro-COVID CSF leukocytes featured an enriched interferon signature; however, this was less pronounced than in viral encephalitis. Repertoire analysis revealed broad clonal T cell expansion and curtailed interferon response in severe compared with mild Neuro-COVID patients. Collectively, our findings document the CSF immune compartment in Neuro-COVID patients and suggest compromised antiviral responses in this setting.

Redefining the heterogeneity of peripheral nerve cells in health and autoimmunity.

Peripheral nerves contain axons and their enwrapping glia cells named Schwann cells (SCs) that are either myelinating (mySCs) or nonmyelinating (nmSCs). Our understanding of other cells in the peripheral nervous system (PNS) remains limited. Here, we provide an unbiased single cell transcriptomic characterization of the nondiseased rodent PNS. We identified and independently confirmed markers of previously underappreciated nmSCs and nerve-associated fibroblasts. We also found and characterized two distinct populations of nerve-resident homeostatic myeloid cells that transcriptionally differed from central nervous system microglia. In a model of chronic autoimmune neuritis, homeostatic myeloid cells were outnumbered by infiltrating lymphocytes which modulated the local cell-cell interactome and induced a specific transcriptional response in glia cells. This response was partially shared between the peripheral and central nervous system glia, indicating common immunological features across different parts of the nervous system. Our study thus identifies subtypes and cell-type markers of PNS cells and a partially conserved autoimmunity module induced in glia cells.

LPA1 signaling drives Schwann cell dedifferentiation in experimental autoimmune neuritis.

BACKGROUND: Lysophosphatidic acid (LPA) is a pleiotropic lipid messenger that addresses at least six specific G-protein coupled receptors. Accumulating evidence indicates a significant involvement of LPA in immune cell regulation as well as Schwann cell physiology, with potential relevance for the pathophysiology of peripheral neuroinflammation. However, the role of LPA signaling in inflammatory neuropathies has remained completely undefined. Given the broad expression of LPA receptors on both Schwann cells and cells of the innate and adaptive immune system, we hypothesized that inhibition of LPA signaling may ameliorate the course of disease in experimental autoimmune neuritis (EAN). METHODS: We induced active EAN by inoculation of myelin protein 2 peptide (P255-78) in female Lewis rats. Animals received the orally available LPA receptor antagonist AM095, specifically targeting the LPA1 receptor subtype. AM095 was administered daily via oral gavage in a therapeutic regimen from 10 until 28 days post-immunization (dpi). Analyses were based on clinical testing, hemogram profiles, immunohistochemistry and morphometric assessment of myelination. RESULTS: Lewis rats treated with AM095 displayed a significant improvement in clinical scores, most notably during the remission phase. Cellular infiltration of sciatic nerve was only discretely affected by AM095. Hemogram profiles indicated no impact on circulating leukocytes. However, sciatic nerve immunohistochemistry revealed a reduction in the number of Schwann cells expressing the dedifferentiation marker Sox2 paralleled by a corresponding increase in differentiating Sox10-positive Schwann cells. In line with this, morphometric analysis of sciatic nerve semi-thin sections identified a significant increase in large-caliber myelinated axons at 28 dpi. Myelin thickness was unaffected by AM095. CONCLUSION: Thus, LPA1 signaling may present a novel therapeutic target for the treatment of inflammatory neuropathies, potentially affecting regenerative responses in the peripheral nerve by modulating Schwann cell differentiation.

Protective effects of 4-aminopyridine in experimental optic neuritis and multiple sclerosis.

Chronic disability in multiple sclerosis is linked to neuroaxonal degeneration. 4-aminopyridine (4-AP) is used and licensed as a symptomatic treatment to ameliorate ambulatory disability in multiple sclerosis. The presumed mode of action is via blockade of axonal voltage gated potassium channels, thereby enhancing conduction in demyelinated axons. In this study, we provide evidence that in addition to those symptomatic effects, 4-AP can prevent neuroaxonal loss in the CNS. Using in vivo optical coherence tomography imaging, visual function testing and histologic assessment, we observed a reduction in retinal neurodegeneration with 4-AP in models of experimental optic neuritis and optic nerve crush. These effects were not related to an anti-inflammatory mode of action or a direct impact on retinal ganglion cells. Rather, histology and in vitro experiments indicated 4-AP stabilization of myelin and oligodendrocyte precursor cells associated with increased nuclear translocation of the nuclear factor of activated T cells. In experimental optic neuritis, 4-AP potentiated the effects of immunomodulatory treatment with fingolimod. As extended release 4-AP is already licensed for symptomatic multiple sclerosis treatment, we performed a retrospective, multicentre optical coherence tomography study to longitudinally compare retinal neurodegeneration between 52 patients on continuous 4-AP therapy and 51 matched controls. In line with the experimental data, during concurrent 4-AP therapy, degeneration of the macular retinal nerve fibre layer was reduced over 2 years. These results indicate disease-modifying effects of 4-AP beyond symptomatic therapy and provide support for the design of a prospective clinical study using visual function and retinal structure as outcome parameters.

Trapped in the epineurium: early entry into the endoneurium is restricted to neuritogenic T cells in experimental autoimmune neuritis.

BACKGROUND: Autoimmune polyneuropathies are acquired inflammatory disorders of the peripheral nervous system (PNS) characterized by inflammation, demyelination, and axonal degeneration. Although the pathogenesis has not been fully elucidated, T cells recognizing self-antigens are believed to initiate inflammation in a subgroup of patients. However, the route and time of T cell entry into the PNS have not yet been described in detail. In this study, we analyzed both kinetics as well as localization of retrovirally transfected green fluorescent protein (GFP)-expressing neuritogenic T lymphocytes in experimental autoimmune neuritis (EAN). METHODS: T lymphocytes obtained from rats following EAN induction by immunization with peripheral nerve protein peptide P255-78 were retrovirally engineered to express GFP. Non-specific T cells were negatively selected by in vitro restimulation, whereas GFP-expressing neuritogenic T cells (reactive to P255-78) were adoptively transferred into healthy rats (AT-EAN). Antigen-specific T cell tracking and localization was performed by flow cytometry and immunohistochemistry during the course of disease. RESULTS: After induction of autoimmune neuritis, P2-reactive T cells were detectable in the liver, spleen, lymph nodes, lung, peripheral blood, and the sciatic nerves with distinct kinetics. A significant number of GFP+ T cells appeared early in the lung with a peak at day four. In the peripheral nerves within the first days, GFP-negative T cells rapidly accumulated and exceeded the number of GFP-expressing cells, but did not enter the endoneurium. Very early after adoptive transfer, T cells are found in proximity to peripheral nerves and in the epineurium. However, only GFP-expressing neuritogenic T cells are able to enter the endoneurium from day five after transfer. CONCLUSIONS: Our findings suggest that neuritogenic T cells invade the PNS early in the course of disease. However, neuritogenic T cells cross the blood-nerve barrier with a certain delay without preference to dorsal roots. Further understanding of the pathophysiological role of autoagressive T cells may help to improve therapeutic strategies in immune-mediated neuropathies.

The Role of Peripheral Myelin Protein 2 in Remyelination.

The protein component of the myelin layer is essential for all aspects of peripheral nerves, and its deficiency can lead to structural and functional impairment. The presence of peripheral myelin protein 2 (P2, PMP2, FABP8, M-FABP) in Schwann cells has been known for decades and shown recently to be involved in the lipid homeostasis in the peripheral neural system. However, its precise role during de- and remyelination has yet to be elucidated. To this end, we assessed remyelination after sciatic nerve crush injury in vivo, and in an experimental de/remyelination ex vivo myelinating culture model in P2-deficient (P2 -/- ) and wild-type (WT) animals. In vivo, the nerve crush paradigm revealed temporal structural and functional changes in P2 -/- mice as compared to WT animals. Concomitantly, P2 -/- DRG cultures demonstrated the presence of shorter internodes and enlarged nodes after ex vivo de/remyelination. Together, these data indicate that P2 may play a role in remyelination of the injured peripheral nervous system, presumably by affecting the nodal and internodal configuration.

Pseudomonas aeruginosa and Its Bacterial Components Influence the Cytokine Response in Thymocytes and Splenocytes.

Infections with Pseudomonas aeruginosa may cause many different diseases. The spectrum of such infections in general includes inflammation and bacterial sepsis. Hospital-acquired pneumonia, naturally resistant to a wide range of antibiotics, is associated with a particularly high mortality rate in mechanically ventilated patients. The pathogenesis of P. aeruginosa is complex and mediated by several virulence factors, as well as cell-associated factors. We have previously demonstrated that stimulation with different bacteria triggers the cytokine response of thymocytes. In this study, we investigated the effect of P. aeruginosa and its different components on the cytokine production of immature and mature immune cells. We found that the induced cytokine pattern in the thymus and the spleen after infections with P. aeruginosa is primarily mediated by lipopolysaccharide (LPS) of the outer cell membrane, but other components of the bacterium can influence the cytokine secretion as well. Stimulation with heat-killed P. aeruginosa and LPS does not influence the amount of cytokine-producing CD4(+) T cells but instead suppresses the emergence of Th17 cells. However, stimulation with P. aeruginosa or its components triggers the interleukin-17 (IL-17) response both in thymocytes and in splenocytes. We conclude that infections with P. aeruginosa affect the cytokine secretion of immature and mature cells and that IL-17 and Th17 cells play only a minor role in the development of pathological systemic inflammatory disease conditions during P. aeruginosa infections. Therefore, other inflammatory immune responses must be responsible for septic reactions of the host.

Alteration of the cytokine signature by various TLR ligands in different T cell populations in MOG37-50 and MOG35-55-induced EAE in C57BL/6 mice.

Interleukin 17 (IL-17), produced by T cells, plays an important role in Multiple Sclerosis (MS) and its animal model, Experimental Autoimmune Encephalomyelitis (EAE). In contrast to IL-17-producing CD4+ T cells, the contribution of IL-17-producing CD8+ T cells (Tc17) in CNS autoimmunity has been investigated less intensively. Here we investigate the role of TC17 in EAE. We compare different T cell populations and their cytokine pattern in the MOG35-55- and MOG37-50-induced EAE. We detected a similar cytokine phenotype for both EAE models in the autoimmune process assessed at different stages. Regarding the migratory activity, an involvement of IL-17 and IFN-γ in disease onset was suggested. Furthermore, we show that PAMPs have the ability to drive autoimmune process. To modify the cytokine pattern of different T cell populations, a combination of distinct factors is required (the activation of MyD88 or Syk, the genetic background, the presence of APCs and CD4+ T cells).

Thymic epithelium determines a spontaneous chronic neuritis in Icam1(tm1Jcgr)NOD mice.

The NOD mouse strain spontaneously develops autoimmune diabetes. A deficiency in costimulatory molecules, such as B7-2, on the NOD genetic background prevents diabetes but instead triggers an inflammatory peripheral neuropathy. This constitutes a shift in the target of autoimmunity, but the underlying mechanism remains unknown. In this study, we demonstrate that NOD mice deficient for isoforms of ICAM-1, which comediate costimulatory functions, spontaneously develop a chronic autoimmune peripheral neuritis instead of diabetes. The disease is transferred by CD4(+) T cells, which infiltrate peripheral nerves together with macrophages and B cells and are autoreactive against peripheral myelin protein zero. These Icam1(tm1Jcgr)NOD mice exhibit unaltered numbers of regulatory T cells, but increased IL-17-producing T cells, which determine the severity, but not the target specificity, of autoimmunity. Ab-mediated ICAM-1 blockade triggers neuritis only in young NOD mice. Thymic epithelium from Icam1(tm1Jcgr)NOD mice features an altered expression of costimulatory molecules and induces neuritis and myelin autoreactivity after transplantation into nude mice in vivo. Icam1(tm1Jcgr)NOD mice exhibit a specifically altered TCR repertoire. Our findings introduce a novel animal model of chronic inflammatory neuropathies and indicate that altered expression of ICAM-1 on thymic epithelium shifts autoimmunity specifically toward peripheral nerves. This improves our understanding of autoimmunity in the peripheral nervous system with potential relevance for human diseases.

Murine guanylate binding protein 2 (mGBP2) controls Toxoplasma gondii replication.

IFN-γ orchestrates the host response against intracellular pathogens. Members of the guanylate binding proteins (GBP) comprise the most abundant IFN-γ-induced transcriptional response. mGBPs are GTPases that are specifically up-regulated by IFN-γ, other proinflammatory cytokines, toll-like receptor agonists, as well as in response to Listeria monocytogenes and Toxoplasma gondii infection. mGBP2 localizes at the parasitophorous vacuole (PV) of T. gondii; however, the molecular function of mGBP2 and its domains in T. gondii infection is not known. Here, we show that mGBP2 is highly expressed in several cell types, including T and B cells after stimulation. We provide evidence that the C-terminal domain is sufficient and essential for recruitment to the T. gondii PV. Functionally, mGBP2 reduces T. gondii proliferation because mGBP2-deficient cells display defects in the replication control of T. gondii. Ultimately, mGBP2-deficient mice reveal a marked immune susceptibility to T. gondii. Taken together, mGBP2 is an essential immune effector molecule mediating antiparasitic resistance.

Natalizumab exerts a suppressive effect on surrogates of B cell function in blood and CSF.

BACKGROUND: Natalizumab for multiple sclerosis (MS) increases the risk of progressive multifocal leukoencephalopathy (PML). OBJECTIVE: We aimed to assess the effect of natalizumab on cellular composition and functional B cell parameters including patients with natalizumab-associated PML (n=37). METHODS: Cellular composition by flow cytometry, levels of immunoglobulin (Ig)G/IgM by immunonephelometry, and oligoclonal bands by isoelectric focusing were studied in blood and cerebrospinal fluid. RESULTS: In MS patients treated with natalizumab without PML (n=59) the proportion of CD19+ B cells was higher in blood, but lower in cerebrospinal fluid compared with MS patients not treated with natalizumab (n=17). The CD4/CD8-ratio in cerebrospinal fluid was lower, and IgG and IgM levels as well as the IgG index dropped in longitudinal samples during natalizumab therapy. Oligoclonal bands persisted, but the total amount of the intrathecally produced IgG fraction, and the polyclonal intrathecal IgG reactivity to measles, rubella, and zoster declined. At the time of diagnosis of PML patients with natalizumab-associated PML had low total IgG levels in blood and cerebrospinal fluid. CONCLUSIONS: Natalizumab impacts B and T cell distribution and exerts an inhibitory effect on surrogates of B cell function in periphery and in cerebrospinal fluid, potentially contributing to the increased risk of developing PML.

Interleukin-17 impedes Schwann cell-mediated myelination.

BACKGROUND: Pro-inflammatory cytokines are known to have deleterious effects on Schwann cells (SCs). Interleukin 17 (IL-17) is a potent pro-inflammatory cytokine that exhibits relevant effects during inflammation in the peripheral nervous system (PNS), and IL-17-secreting cells have been reported within the endoneurium in proximity to the SCs. METHODS: Here, we analyzed the effects of IL-17 on myelination and the immunological properties of SCs. Dorsal root ganglia (DRG) co-cultures containing neurons and SCs from BL6 mice were used to define the impact of IL-17 on myelination and on SC differentiation; primary SCs were analyzed for RNA and protein expression to define the putative immunological alignment of the SCs. RESULTS: SCs were found to functionally express the IL-17 receptors A and B. In DRG cultures, stimulation with IL-17 resulted in reduced myelin synthesis, while pro-myelin gene expression was suppressed at the mRNA level. Neuronal outgrowth and SC viability, as well as structural myelin formation, remained unaffected. Co-cultures exhibited SC-relevant pro-inflammatory markers, such as matrix metalloproteinase 9 and SCs significantly increased the expression of the major histocompatibility complex (MHC) I and exhibited a slight, nonsignificant increase in expression of MHCII, and a transporter associated with antigen presentation (TAP) II molecules relevant for antigen processing and presentation. CONCLUSIONS: IL-17 may act as a myelin-suppressive mediator in the peripheral nerve, directly propagating SC-mediated demyelination, paralleled by an inflammatory alignment of the SCs. Further analyses are warranted to elucidate the role of IL-17 during inflammation in the PNS in vivo, which could be useful in the development of target therapies.

Cytokines (IL1ß, IL6, TNFα) and serum cortisol levels may not constitute reliable biomarkers to identify individuals with post-acute sequelae of COVID-19.

Background: Post-acute sequelae of COVID-19 (PASC) comprise a broad spectrum of symptoms such as fatigue, general weakness, compromised attention and sleep or anxiety disorders. PASC represents a medical and socio-economic challenge. Objectives: Our study evaluated cytokines (IL-1ß, IL-6 and TNFα) and cortisol levels in a cohort of typical patients with PASC, suffering concentration problems, fatigue and difficulties finding words. Design: This was a prospective cohort study. Four groups were analysed and compared: those who had never contracted SARS-CoV-2 (n = 13), infected but had no PASC (n = 34), infected with former PASC that resolved (n = 40) and patients with ongoing PASC after infection (n = 91). Methods: Cytokine and cortisol serum levels were determined in patients' blood samples. Results: Cytokine levels of IL-1ß, IL-6, TNFα and cortisol levels did not differ between groups analysed. Conclusion: This may indicate a non-organic/psychosomatic genesis of PASC; further studies are needed to elucidate the underlying causes of PACS, and non-organic causes should not be overlooked.

Without clear biological markers for people who will continue to present with post-acute sequelae of COVID-19 (PASC) should we now focus on psychological factors? Many people across the globe are still suffering from post-acute sequelae of COVID-19 (PASC), commonly called post-COVID. Typical symptoms of PASC include severe tiredness (fatigue), concentration deficits (brain fog) or difficulty finding words. We need a better understanding of how these symptoms arise to find ways to help patients. Our team of researchers set out to explore this. We posed the question: could measurements of immune system activity provide an identifier for people who are susceptible to post-COVID? The participants in our study were divided into four groups: 1. A group of 13 people who had never contracted SARS-CoV-2. 2. A group of 34 people who had been infected with SARS-CoV-2 but had no PASC. 3. A group of 40 people who had been infected with SARS-CoV-2 and had already suffered from PASC that had now resolved. 4. A group of 91 people who were no longer sick with COVID-19 but were still suffering from PASC. Serum samples from all participants were taken to measure cytokine and cortisol levels. People with PASC could not be identified by testing their blood samples for cytokines (IL-1ß, IL-6, TNFα) or cortisol. No difference between the four groups was found on any marker. Measuring these cytokines or cortisol is, therefore, unlikely to be useful in predicting which patients will suffer from PASC. Continuation of symptoms long after COVID-19 has passed is distressing for many people worldwide. Psychological factors may play a role and need to be studied further in order to help this patient population.

Preventing long-term disability in CIDP: the role of timely diagnosis and treatment monitoring in a multicenter CIDP cohort.

BACKGROUND: Chronic inflammatory demyelinating polyneuropathy (CIDP) is an inflammatory disease affecting the peripheral nerves and the most frequent autoimmune polyneuropathy. Given the lack of established biomarkers or risk factors for the development of CIDP and patients' treatment response, this research effort seeks to identify potential clinical factors that may influence disease progression and overall treatment efficacy. METHODS: In this multicenter, retrospective analysis, we have screened 197 CIDP patients who presented to the University Hospitals in Düsseldorf, Berlin, Cologne, Essen, Magdeburg and Munich between 2018 and 2022. We utilized the respective hospital information system and examined baseline data with clinical examination, medical letters, laboratory results, antibody status, nerve conduction studies, imaging and biopsy findings. Aside from clinical baseline data, we analyzed treatment outcomes using the Standard of Care (SOC) definition, as well as a comparison of an early (within the first 12 months after manifestation) versus late (more than 12 months after manifestation) onset of therapy. RESULTS: In terms of treatment, most patients received intravenous immunoglobulin (56%) or prednisolone (39%) as their first therapy. Patients who started their initial treatment later experienced a worsening disease course, as reflected by a significant deterioration in their Inflammatory Neuropathy Cause and Treatment (INCAT) leg disability score. SOC-refractory patients had worse clinical outcomes than SOC-responders. Associated factors for SOC-refractory status included the presence of fatigue as a symptom and alcohol dependence. CONCLUSION: Timely diagnosis, prompt initiation of treatment and careful monitoring of treatment response are essential for the prevention of long-term disability in CIDP and suggest a "hit hard and early" treatment paradigm.

In astrocytes the accumulation of the immunity-related GTPases Irga6 and Irgb6 at the vacuole of Toxoplasma gondii is dependent on the parasite virulence.

Toxoplasma gondii is an obligate intracellular protozoan parasite responsible for a common infection of the central nervous system. Interferon (IFN) γ is the key cytokine of host defence against T. gondii. However, T. gondii strains differ in virulence and T. gondii factors determining virulence are still poorly understood. In astrocytes IFN γ primarily induces immunity-related GTPases (IRGs), providing a cell-autonomous resistance system. Here, we demonstrate that astrocytes prestimulated with IFN γ inhibit the proliferation of various avirulent, but not virulent, T. gondii strains. The two analyzed immunity-related GTPases Irga6 and Irgb6 accumulate at the PV only of avirulent T. gondii strains, whereas in virulent strains this accumulation is only detectable at very low levels. Both IRG proteins could temporarily be found at the same PV, but did only partially colocalize. Coinfection of avirulent and virulent parasites confirmed that the accumulation of the two analyzed IRGs was a characteristic of the individual PV and not determined by the presence of other strains of T. gondii in the same host cell. Thus, in astrocytes the accumulation of Irga6 and Irgb6 significantly differs between avirulent and virulent T. gondii strains correlating with the toxoplasmacidal properties suggesting a role for this process in parasite virulence.

Time for a standardized diagnostic response test in patients with chronic inflammatory demyelinating polyradiculoneuropathy?

Standardized pharmacological response tests are important and established diagnostic tools in the field of neurology. However, regarding therapeutic responses to intravenous immunoglobulins (IVIg) in CIDP, neither a definition of therapeutic response has been established, nor a response test has been suggested so far. Here we suggest a practical clinical approach which is supported by current literature in the field. An established standardized IVIg response test could avoid prolonged therapy without benefit for the patient and ensure a timely therapy switch or treatment escalation if required. This approach would also be advantageous due to the global scarcity of plasma derivatives as a human resource and could be the foundation to be adjusted and improved by subsequent studies.

Impact of NKG2D Signaling on Natural Killer and T-Cell Function in Cerebral Ischemia.

Background Typically defined as a thromboinflammatory disease, ischemic stroke features early and delayed inflammatory responses, which determine the extent of ischemia-related brain damage. T and natural killer cells have been implicated in neuronal cytotoxicity and inflammation, but the precise mechanisms of immune cell-mediated stroke progression remain poorly understood. The activating immunoreceptor NKG2D is expressed on both natural killer and T cells and may be critically involved. Methods and Results An anti-NKG2D blocking antibody alleviated stroke outcome in terms of infarct volume and functional deficits, coinciding with reduced immune cell infiltration into the brain and improved survival in the animal model of cerebral ischemia. Using transgenic knockout models devoid of certain immune cell types and immunodeficient mice supplemented with different immune cell subsets, we dissected the functional contribution of NKG2D signaling by different NKG2D-expressing cells in stroke pathophysiology. The observed effect of NKG2D signaling in stroke progression was shown to be predominantly mediated by natural killer and CD8+ T cells. Transfer of T cells with monovariant T-cell receptors into immunodeficient mice with and without pharmacological blockade of NKG2D revealed activation of CD8+ T cells irrespective of antigen specificity. Detection of the NKG2D receptor and its ligands in brain samples of patients with stroke strengthens the relevance of preclinical observations in human disease. Conclusions Our findings provide a mechanistic insight into NKG2D-dependent natural killer- and T-cell-mediated effects in stroke pathophysiology.

Severe and long-lasting alteration of albumin redox state by plasmapheresis.

Plasmapheresis (PE) is an established form of therapeutic apheresis (TA). Purpose of this longitudinal prospective single center study was to investigate the effect of PE on albumin redox state (ARS), as infusion of commercial albumin during PE may alter albumin oxidation which has an impact on its functional properties and oxidative stress level. 43 subjects with autoimmune-mediated neurological disorders were included. 20 subjects in the experimental group received five treatments of PE. 13 subjects received five treatments of immunoadsorption and 10 subjects received no TA as controls. ARS was determined before and after TA and 12 days after the last TA by fractionating it into human mercaptalbumin (HMA), human non-mercaptalbumin 1 (HNA-1), and human non-mercaptalbumin 2 (HNA-2) by high-performance liquid chromatography. Irreversibly oxidised HNA-2 increased over the course of five PE treatments from 2.8% (IQR 1.3-3.7%) to 13.6% (IQR 10.9-15.9) (P < 0.01) and remained elevated 12 days after the last PE procedure (7.7% IQR 7.1-10.5, P < 0.05). The study showed for the first time that PE exerts a severe and long-lasting alteration on ARS indicating a new adverse effect of PE, that may influence oxidative stress level.