Assessment of longitudinal serum neutrophil extracellular trap-inducing activity in anti-neutrophil cytoplasmic antibody-associated vasculitis and glomerulonephritis in a prospective cohort using a novel bio-impedance technique.

Neutrophil extracellular traps (NET) have been implicated in the pathogenesis of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Here, we developed a novel, label-free, high-throughput bio-impedance technique to effectively measure serum NET-inducing activity. Using this technique, NET-inducing activity of serum derived from patients with AAV was assessed in a prospective cohort of 62 patients presenting with active AAV with major organ involvement. Thirty-five patients presented with new and 27 patients presented with relapsing AAV, of whom 38 had kidney and/or 31 had lung involvement. NET-inducing activity was assessed at diagnosis of active AAV (time zero), during the first 6 weeks of treatment, and after 6 months of treatment. Forty-seven patients revealed elevated NET-inducing activity at time zero. After initiation of immunosuppressive treatment, NET-inducing activity was reduced at six weeks. A subsequent increase at six months could potentially identify patients with relapsing disease (hazard ratio, 11.45 [interquartile range 1.36-96.74]). NET-inducing activity at time zero correlated with kidney function and proteinuria. Importantly, in kidney tissue, NETs co-localized with lesions typical of ANCA-associated glomerulonephritis and even correlated with systemic serum NET-inducing activity. Thus, our prospective data corroborate the importance of NET formation in AAV and ANCA-associated glomerulonephritis and the potential of longitudinal evaluation, as monitored by our novel bio-impedance assay and detailed histological evaluation.

CD163 and CD206 expression define distinct macrophage subsets involved in active ANCA-associated glomerulonephritis.

INTRODUCTION: Macrophages are key players in the immunopathology of anti-neutrophil cytoplasmic antibody (ANCA) mediated-vasculitis (AAV) with glomerulonephritis (ANCA GN). Different macrophage phenotypes are expected to play distinct roles in ANCA GN. Macrophages expressing CD163 and CD206 are found in lesions associated with ANCA GN. Hence, we aimed to investigate the clinicopathological significance of CD206 and CD163 in ANCA GN in a multicenter retrospective cohort study. MATERIAL AND METHODS: Patients with ANCA-associated vasculitis, with clinical data, serum and urine samples were included from three cohorts. Serum soluble CD206 (ssCD206) and urinary soluble CD163 (usCD163) levels were measured. Human kidney tissue samples (n = 53) were stained for CD206 and CD163 using immunohistochemistry and immunofluorescence, and findings were correlated with clinical and pathological data. RESULTS: In total, 210 patients were included (i.e., ANCA GN, n = 134; AAV without GN, n = 24; AAV in remission n = 52). Increased levels of both ssCD206 and usCD163 were seen in ANCA GN. High levels of ssCD206 declined after reaching remission, however, ssCD206 did not improve the accuracy of usCD163 to detect ANCA GN. Soluble markers correlated with histopathological findings. CD163+CD206- macrophages were found in the glomerulus and may play pivotal roles in glomerulonephritis, whereas CD206+CD163- and CD206+CD163+ macrophages were located tubulointerstitially and likely play a more prominent role in ANCA-associated tubulointerstitial inflammation. In ANCA GN patients increasing levels of ssCD206 increased the risk for end-stage renal disease and mortality. CONCLUSIONS: Our results confirm and extend the notion that CD206+ and CD163+ macrophages are prominent components of the cellular infiltrate in ANCA GN. We found distinct macrophage phenotypes that may play distinct roles in the immunopathology of ANCA GN and elaborate on a potential mechanism underlying the findings of this study. usCD163 remains an excellent marker to detect active ANCA GN, whereas ssCD206 seems a more prominent marker for risk prediction.

The natural course of pregnancies in women with primary atypical haemolytic uraemic syndrome and asymptomatic relatives.

Pregnancy has been linked to various microangiopathies, including primary atypical haemolytic uraemic syndrome (aHUS). Complement dysregulation, often linked to rare variants in complement genes, is key for primary aHUS to manifest and may play a role in pregnancy complications of the mother and fetus. The burden of such complications is unknown, making counselling of women with primary aHUS and asymptomatic relatives difficult. We analyzed the maternal and fetal outcomes of 39 pregnancies from 17 women with primary aHUS and two asymptomatic relatives. Seven out of 39 pregnancies were complicated by pregnancy-associated aHUS. Five out of 32 pregnancies not linked to pregnancy-associated aHUS were complicated by pre-eclampsia or HELLP. Rare genetic variants were identified in 10 women (asymptomatic relatives, n = 2) who had a total of 14 pregnancies, including 10 uncomplicated pregnancies. Thirty-five out of 39 pregnancies resulted in live birth. Eight out of 19 women had progressed to end-stage kidney disease, with an incidence of 2·95 (95% confidence interval, 1·37-5·61) per 100 person-years after the first pregnancy. Thus, we emphasized the frequency of successful pregnancies in women with primary aHUS and asymptomatic relatives. Pregnancies should be monitored closely. Rare genetic variants cannot predict the risk of a given pregnancy.

C5b9 Formation on Endothelial Cells Reflects Complement Defects among Patients with Renal Thrombotic Microangiopathy and Severe Hypertension.

Background Severe hypertension can induce thrombotic microangiopathy (TMA) in the renal vasculature, the occurrence of which has been linked to mechanical stress to the endothelium. Complement defects may be the culprit of disease in patients who present with severe renal disease and often progress to ESRD, despite BP control.Methods We studied a well defined cohort of 17 patients with hypertension-associated TMA to define the prevalence of complement defects by a specific ex vivo serum-based microvascular endothelial cell assay.Results Compared with normal human serum and samples from patients with hypertensive arterionephrosclerosis, 14 of 16 (87.5%) serum samples collected at presentation from 16 patients with hypertension-associated TMA induced abnormal C5b9 formation on microvascular endothelial cells. We detected rare variants in complement genes in eight of 17 (47%) patients. ESRD occurred in 14 of 17 (82%) patients, and recurrent TMA after transplant occurred in seven of 11 (64%) donor kidneys. Eculizumab improved the renal function in three patients and prevented TMA recurrence in an allograft recipient.Conclusions These observations point to complement defects as the key causative factor of ESRD and recurrent TMA after transplant in patients presenting with severe hypertension. Complement defects can be identified by measurements of complement activation on microvascular endothelial cells, which should substantially influence treatment and prognosis.

Anti-GAD antibodies in a cohort of neuropsychiatric patients.

OBJECTIVE: Antiglutamate decarboxylase (anti-GAD) antibodies are associated with several neurological manifestations, like epilepsy and movement disorders. However, in daily neurological practice, it remains hard to define when to test for anti-GAD antibodies in patients with neurologic and/or psychiatric symptoms. Therefore, here, we report the patient characteristics of a large retrospective cohort of patients tested for anti-GAD antibodies in clinical practice and compare the characteristics of anti-GAD positive and anti-GAD negative patients. METHODS: We blindly assessed relevant clinical symptoms and comorbidities and functional outcome with the modified Rankin Scale (mRS) in a retrospective observational cohort of all patients in which the decision to assess anti-GAD levels had been made based solely on the presence of possible associated neurological and/or psychiatric symptoms (N=119). RESULTS: Out of 119 patients, 17 (14.3%) were anti-GAD positive. The anti-GAD positive patients had a median age of 30years (range: 3-64; 2 children). They all had epilepsy, with 8 (47%) patients reporting cognitive complaints. Psychiatric symptoms were less prevalent in anti-GAD positive patients, only 1 anti-GAD positive patient (6%) versus 34 anti-GAD negative patients (33%) reported psychiatric symptoms (p=0.021). The most frequent comorbidity of anti-GAD positive patients was diabetes mellitus type 1 (n=8). Twelve (71%) and 13 (78%) of the anti-GAD positive patients were functionally independent at the time of diagnosis and after one year, respectively (mRS score: 0 to 2). There was no significant difference in functional status at any time during follow-up compared with the anti-GAD negative group. CONCLUSION: Antiglutamate decarboxylase (anti-GAD) antibodies relate to epilepsy with or without cognitive complaints. However, psychiatric symptoms were almost absent in anti-GAD positive patients, and the presence of anti-GAD antibodies contributed little to the prognosis in our cohort.

Patients with hypertension-associated thrombotic microangiopathy may present with complement abnormalities.

Thrombotic microangiopathy (TMA) is a pattern of endothelial damage that can be found in association with diverse clinical conditions such as malignant hypertension. Although the pathophysiological mechanisms differ, accumulating evidence links complement dysregulation to various TMA syndromes and in particular the atypical hemolytic uremic syndrome. Here, we evaluated the role of complement in nine consecutive patients with biopsy-proven renal TMA attributed to severe hypertension. Profound hematologic symptoms of TMA were uncommon. In six out of nine patients, we found mutations C3 in three, CFI in one, CD46 in one, and/or CFH in two patients either with or without the risk CFH-H3 haplotype in four patients. Elevated levels of the soluble C5b-9 and renal deposits of C3c and C5b-9 along the vasculature and/or glomerular capillary wall, confirmed complement activation in vivo. In contrast to patients without genetic defects, patients with complement defects invariably progressed to end-stage renal disease, and disease recurrence after kidney transplantation seems common. Thus, a subset of patients with hypertension-associated TMA falls within the spectrum of complement-mediated TMA, the prognosis of which is poor. Hence, testing for genetic complement abnormalities is warranted in patients with severe hypertension and TMA on renal biopsy to adopt suitable treatment options and prophylactic measures.

Performance analysis of automated evaluation of Crithidia luciliae-based indirect immunofluorescence tests in a routine setting - strengths and weaknesses.

BACKGROUND: Antibodies directed against dsDNA are a highly specific diagnostic marker for the presence of systemic lupus erythematosus and of particular importance in its diagnosis. To assess anti-dsDNA antibodies, the Crithidia luciliae-based indirect immunofluorescence test (CLIFT) is one of the assays considered to be the best choice. To overcome the drawback of subjective result interpretation that inheres indirect immunofluorescence assays in general, automated systems have been introduced into the market during the last years. Among these systems is the EUROPattern Suite, an advanced automated fluorescence microscope equipped with different software packages, capable of automated pattern interpretation and result suggestion for ANA, ANCA and CLIFT analysis. METHODS: We analyzed the performance of the EUROPattern Suite with its automated fluorescence interpretation for CLIFT in a routine setting, reflecting the everyday life of a diagnostic laboratory. Three hundred and twelve consecutive samples were collected, sent to the Central Diagnostic Laboratory of the Maastricht University Medical Centre with a request for anti-dsDNA analysis over a period of 7 months. RESULTS: Agreement between EUROPattern assay analysis and the visual read was 93.3%. Sensitivity and specificity were 94.1% and 93.2%, respectively. The EUROPattern Suite performed reliably and greatly supported result interpretation. CONCLUSIONS: Automated image acquisition is readily performed and automated image classification gives a reliable recommendation for assay evaluation to the operator. The EUROPattern Suite optimizes workflow and contributes to standardization between different operators or laboratories.

CD4+CD28null T Cells are related to previous cytomegalovirus infection but not to accelerated atherosclerosis in ANCA-associated vasculitis.

Previous studies have suggested an increased risk for cardiovascular events in antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV). We analyzed the presence of atherosclerotic damage in patients with AAV in relation to the presence of CD4+CD28null T cells and antibodies against cytomegalovirus (CMV) and human Heat-Shock Protein 60 (hHSP60). In this cross-sectional study, patients with inactive AAV were compared with healthy controls (HC). Carotid intima-media thickness (IMT) and aortic pulse-wave velocity (PWV) were measured. In addition, CD4+CD28null T cells, anti-CMV, and anti-hHSP60 levels were determined. Forty patients with AAV were included. Patients' spouses were recruited as HC (N = 38). CD4+CD28null T cells are present in patients with AAV in a higher percentage (median 3.1, range 0.01-85) than in HC (0.28, 0-36, P < 0.0001). No significant difference in IMT (mm) between patients and controls was detected (mean 0.77 ± standard deviation 0.15 and 0.73 ± 0.11, respectively, P = 0.20). PWV standardized for MAP was increased in AAV patients (9.80 ± 2.50 m/s, compared to 8.72 ± 1.68 in HC, P = 0.04). There was a strong association between a previous CMV infection and the presence and percentage of CD4+CD28null T cells (0.33 vs 13.8, P < 0.001). There was no relationship between CD4+CD28null T cells and/or a previous CMV infection and IMT or PWV. There was no relation between anti-hHSP60 and CD4+CD28null T cells. Increased PWV values suggest atherosclerotic damage in patients with AAV. Plaque size, as determined by IMT, did not differ. CD4+CD28null T cells are increased in AAV and related to the previous CMV infection.

Anti-PLA2R Antibodies as a Prognostic Factor in PLA2R-Related Membranous Nephropathy.

BACKGROUND: The natural course of idiopathic membranous nephropathy (MN) varies, as it is known through favorable outcomes in most patients. However, one third of patients with idiopathic MN will slowly progress to end-stage renal disease (ESRD). To prevent disease progression, patients at high risk to develop ESRD are treated with immunosuppressive agents. Therefore, a correct selection of patients who need immunosuppressive treatment is important. METHODS: Here, we evaluated the prognostic value of anti-phospholipase A2 receptor 1 antibody (anti-PLA2R) levels regarding clinical outcome in a well-defined cohort of 73 PLA2R-related MN patients with long-term follow-up. At baseline, patients were subdivided into patients with either low or high antibody levels based on ELISA testing. RESULTS: Spontaneous remission rates were highest among patients with low anti-PLA2R levels (79%; hazard ratio 2.72 (95% CI 1.22-6.08), p = 0.02) after a median follow-up of 2.9 (95% CI 0.8-5.0, p < 0.001) years, whereas high anti-PLA2R levels were associated with persistent proteinuria (p = 0.04) and/or the need for immunosuppressive therapy (p < 0.001). Renal survival rates were 97% at 5 years, 93% at 10 years, and 89% at 15 years; however, this was not different between the anti-PLA2R groups. ESRD occurred significantly faster in patients with severe proteinuria as compared to patients with either mild (p = 0.02) or moderate proteinuria (p = 0.05). CONCLUSIONS: Low anti-PLA2R levels may predict spontaneous remissions in patients with PLA2R-related MN. Therefore, we suggest that quantification of anti-PLA2R is of value to monitor these patients.

The intrinsic coagulation pathway plays a dominant role in driving hypercoagulability in ANCA-associated vasculitis.

ABSTRACT: The risk of a venous thrombotic event (VTE) is increased in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV); however, a detailed understanding of the underlying mechanisms of hypercoagulability is limited. We assessed prospectively different coagulation parameters in 71 patients with active AAV at baseline and after 6 months of follow-up. D-dimers and fibrinogen were increased in most patients at presentation and remained elevated in half of the patients. Particularly, thrombin-antithrombin (T:AT) complex and activated coagulation factors in complex with their natural inhibitors of the intrinsic coagulation pathway (ie, activated FXII:C1 esterase inhibitor [FXIIa:C1Inh], FXIa:AT, and FXIa:alpha1-antitrypsin [FXIa:α1AT]) were profoundly elevated in patients at baseline. Thrombin formation was dominantly correlated with coagulation factors of the intrinsic pathway (ie, FXIIa:AT, FXIa:AT, FXIa:α1AT, and FXIa:C1Inh) compared to the extrinsic pathway (ie, FVIIa:AT). Hypercoagulability correlated with higher disease activity, ANCA levels, C-reactive protein, serum creatinine, and proteinuria. VTEs were observed in 5 out of 71 (7%) patients within 1 month (interquartile range, 1-5) after inclusion. Baseline T:AT levels were significantly higher in patients with VTE than in those without VTE (P = .044), but other clinical or laboratory markers were comparable between both groups. Hypercoagulability is dominantly characterized by activation of the intrinsic coagulation pathway and elevated D-dimers in active AAV. The driving factors of hypercoagulability are yet to be studied but are most likely related to an interplay of increased disease activity, vascular inflammation, and endothelial damage. Future targets for intervention could include inhibitors of the intrinsic coagulation pathway and compounds specifically reducing the hyperinflammatory state.

Adding low dose cyclophosphamide to rituximab for remission-induction may prolong relapse-free survival in patients with ANCA vasculitis: A retrospective study.

Objective: Rituximab (RTX) and cyclophosphamide (CYC) are effective remission-induction therapies in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). However, combining these therapies may favor prognosis in patients with a major disease presentation. We conducted a retrospective study to compare patients treated with a combination of RTX and low dose CYC (RTX-CYC) or with RTX only, both followed by tailored maintenance with RTX, with regard to long-term outcomes. Methods: Patients treated in the Maastricht University Medical Center between March 2007 and January 2019, were screened for eligibility. The primary outcome variable was major relapse rate after two and five years. Secondary outcome variables were clinical data and laboratory parameters. Results: Of the 246 screened patients, 34 received RTX-CYC and 28 RTX only for remission-induction. All patients were followed for at least two years, with a median follow-up of 48 months (IQR 24-60). At baseline, renal involvement was more prevalent in the RTX-CYC patients (85% vs. 61%, P = 0.028). Major relapse rates within two years, but not after five years, were significantly lower in the RTX-CYC group (3% vs. 24%, P = 0.032). The rate of infections, hypogammaglobulinemia, end-stage renal disease, malignancies, and mortality did not differ after two and five years. Conclusion: Adding low dose CYC to RTX is safe and may prevent major relapses in patients with severe AAV in the first two years after remission-induction. Randomized controlled trials that compare the efficacy and safety between RTX and a combination of RTX with CYC are needed.

Identifying therapeutic monoclonal antibodies using target protein collision electrophoresis reflex assay to separate the wheat from the chaff.

Monoclonal gammopathies are characterized by the presence of monoclonal immunoglobulins, also known as M-proteins. Therapeutic monoclonal antibodies (t-mAbs) can interfere in laboratory assays used to monitor the state of disease, such as serum protein electrophoresis (SPE) and immunofixation electrophoresis (IFE). To establish a correct interpretation of IFE, Target protein-Collision Immunofixation Electrophoresis Reflex Assay (T-CIERA) was developed to identify t-mAbs in IFE. Here we demonstrate that T-CIERA is applicable to a wide variety of t-mAbs for which the target protein is commercially available. Moreover, the shift observed was characteristic for each t-mAb, and T-CIERA enabled the identification of multiple t-mAbs sharing a common target protein. Additionally, the lower limit of detection (LLOD) was determined objectively, and T-CIERA demonstrated an adequate LLOD for all tested t-mAbs. Furthermore, T-CIERA was also successfully applied to serum samples obtained from patients receiving daratumumab, isatuximab, elotuzumab, and durvalumab treatment. In conclusion, T-CIERA is a suitable reflex assay for identifying a wide variety of t-mAbs, including those for which no commercial assay is available to deal with their interference. Moreover, CD38-CIERA could serve as an alternative or complementary test to the commercially available Hydrashift assay kits. T-CIERA would enable laboratories without mass spectrometry equipment and expertise in this area to distinguish between drug and disease to improve clinical response monitoring and diagnosis of monoclonal gammopathies.

Anti-GAD65 autoantibody levels measured by ELISA and alternative types of immunoassays in relation to neuropsychiatric diseases versus diabetes mellitus type 1.

Background: Anti-GAD65 autoantibodies (GAD65-Abs) may occur in patients with epilepsy and other neurological disorders, but the clinical significance is not clear-cut. Whereas high levels of GAD65-Abs are considered pathogenic in neuropsychiatric disorders, low or moderate levels are only considered as mere bystanders in, e.g., diabetes mellitus type 1 (DM1). The value of cell-based assays (CBA) and immunohistochemistry (IHC) for GAD65-Abs detection has not been clearly evaluated in this context. Objective: To re-evaluate the assumption that high levels of GAD65-Abs are related to neuropsychiatric disorders and lower levels only to DM1 and to compare ELISA results with CBA and IHC to determine the additional value of these tests. Methods: 111 sera previously assessed for GAD65-Abs by ELISA in routine clinical practice were studied. Clinical indications for testing were, e.g., suspected autoimmune encephalitis or epilepsy (neuropsychiatric cohort; n = 71, 7 cases were initially tested positive for GAD65-Abs by ELISA), and DM1 or latent autoimmune diabetes in adults (DM1/LADA cohort (n = 40, all were initially tested positive)). Sera were re-tested for GAD65-Abs by ELISA, CBA, and IHC. Also, we examined the possible presence of GAD67-Abs by CBA and of other neuronal autoantibodies by IHC. Samples that showed IHC patterns different from GAD65 were further tested by selected CBAs. Results: ELISA retested GAD65-Abs level in patients with neuropsychiatric diseases was higher than in patients with DM1/LADA (only retested positive samples were compared; 6 vs. 38; median 47,092 U/mL vs. 581 U/mL; p = 0.02). GAD-Abs showed positive both by CBA and IHC only if antibody levels were above 10,000 U/mL, without a difference in prevalence between the studied cohorts. We found other neuronal antibodies in one patient with epilepsy (mGluR1-Abs, GAD-Abs negative), and in a patient with encephalitis, and two patients with LADA. Conclusion: GAD65-Abs levels are significantly higher in patients with neuropsychiatric disease than in patients with DM1/LADA, however, positivity in CBA and IHC only correlates with high levels of GAD65-Abs, and not with the underlying diseases.

Plasma Dephosphorylated-Uncarboxylated Matrix Gla-Protein in Systemic Sclerosis Patients: Biomarker Potential for Vascular Calcification and Inflammation.

BACKGROUND: Systemic sclerosis (SSc) patients face an elevated risk of cardiovascular disease (CVD), even when classic cardiovascular risk factors are considered. Plasma dephosphorylated-uncarboxylated Matrix Gla-protein (dp-ucMGP), an inactive form of MGP, is associated with increased CVD risk. Smooth muscle cells, implicated in SSc's development, are the primary dp-ucMGP producers. This study assessed dp-ucMGP levels and initial CVD events in early-diagnosed SSc patients, investigating its potential as a CVD and all-cause mortality predictor over time. METHODS: In a cohort of 87 SSc patients (excluding those with pre-existing CVD or on dialysis), baseline dp-ucMGP levels were measured, along with cardiovascular risk factors. Validation involved assessing dp-ucMGP in a subset of treatment-naive SSc patients. RESULTS: A significantly elevated median dp-ucMGP level of 634 pmol/L (IQR 301) compared with healthy controls (dp-ucMGP < 393 pmol/L; p < 0.001) was observed. Validation in a treatment-naive SSc patient subset yielded similar results (median 589 pmol/L; IQR 370). During a median 10.5-year follow-up among 78 SSc patients, 33.3% experienced their first CVD event, independent of traditional risk factors. Elevated dp-ucMGP levels (>634 pmol/L) correlated with a higher risk of CVD and/or death (log-rank test: p < 0.01). CONCLUSIONS: In summary, dp-ucMGP emerges as a novel biomarker in SSc patients, with elevated levels indicating an increased risk of CVD and/or mortality in this population.

Hypoxia-Driven Changes in a Human Intestinal Organoid Model and the Protective Effects of Hydrolyzed Whey.

Many whey proteins, peptides and protein-derived amino acids have been suggested to improve gut health through their anti-oxidant, anti-microbial, barrier-protective and immune-modulating effects. Interestingly, although the degree of hydrolysis influences peptide composition and, thereby, biological function, this important aspect is often overlooked. In the current study, we aimed to investigate the effects of whey protein fractions with different degrees of enzymatic hydrolysis on the intestinal epithelium in health and disease with a novel 2D human intestinal organoid (HIO) monolayer model. In addition, we aimed to assess the anti-microbial activity and immune effects of the whey protein fractions. Human intestinal organoids were cultured from adult small intestines, and a model enabling apical administration of nutritional components during hypoxia-induced intestinal inflammation and normoxia (control) in crypt-like and villus-like HIO was established. Subsequently, the potential beneficial effects of whey protein isolate (WPI) and two whey protein hydrolysates with a 27.7% degree of hydrolysis (DH28) and a 50.9% degree of hydrolysis (DH51) were assessed. In addition, possible immune modulatory effects on human peripheral immune cells and anti-microbial activity on four microbial strains of the whey protein fractions were investigated. Exposure to DH28 prevented paracellular barrier loss of crypt-like HIO following hypoxia-induced intestinal inflammation with a concomitant decrease in hypoxia inducible factor 1 alpha (HIF1α) mRNA expression. WPI increased Treg numbers and Treg expression of cluster of differentiation 25 (CD25) and CD69 and reduced CD4+ T cell proliferation, whereas no anti-microbial effects were observed. The observed biological effects were differentially mediated by diverse whey protein fractions, indicating that (degree of) hydrolysis influences their biological effects. Moreover, these new insights may provide opportunities to improve immune tolerance and promote intestinal health.

Predictive Value of Serum Neurofilament Light Chain Levels in Anti-NMDA Receptor Encephalitis.

BACKGROUND AND OBJECTIVES: Determinants of disease activity and prognosis are limited in anti-NMDA receptor (NMDAR) encephalitis. Neurofilament light chains (NfL) are markers of axonal damage and have been identified as valuable biomarkers for neurodegenerative and other neuroinflammatory disorders. We aimed to investigate serum NfL levels in patients with anti-NMDAR encephalitis as a biomarker for disease severity and outcome. METHODS: In this retrospective study, NfL values were measured in all available pretreatment serum and paired CSF samples of the nationwide anti-NMDAR encephalitis cohort. The values were analyzed in duplicate using single-molecule array and compared with measurements in healthy references. Follow-up sera were tested to analyze longitudinal responsiveness, if at least available from 2 time points after diagnosis. Serum NfL levels were compared with data on disease activity (seizures, MRI, and CSF findings), severity (modified Rankin Scale [mRS] score, admission days, and intensive care unit admission), and outcome (mRS score and relapses), using regression analysis. RESULTS: We have included 71 patients (75% female; mean age 31.4 years, range 0-85 years) of whom pretreatment serum samples were analyzed. Paired CSF samples were available of 33 patients, follow-up serum samples of 20 patients. Serum NfL levels at diagnosis were higher in patients (mean 19.5 pg/mL, 95% CI 13.7-27.7) than in references (mean 6.4 pg/mL, 95% CI 5.8-7.2, p < 0.0001). We observed a good correlation between serum and CSF NfL values (R = 0.84, p < 0.0001). Serum NfL levels and age correlated in patients (Pearson R = 0.57, p < 0.0001) and references (R = 0.62, p < 0.0001). Increased NfL values were detected in patients post-herpes simplex virus 1 encephalitis (mean 248.8 vs 14.1 pg/mL, p < 0.0001) and in patients with brain MRI lesions (mean 27.3 vs 11.1 pg/mL, p = 0.019). NfL levels did relate to the long-term follow-up (mRS score at 12 months; ßNfL = 0.55, p = 0.013), although largely explained by the effect of age on NfL levels and prognosis. In serial samples, NfL values did roughly follow clinical disease activity, albeit with delay. DISCUSSION: Increased serum NfL levels reflect neuroaxonal damage in anti-NMDAR encephalitis. No relationship was identified with disease severity, whereas the association with outcome was confounded by age. The implied role of sampling timing on NfL levels also limits the applicability of NfL as a prognostic marker.