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Multiple sclerosis (MS) and stroke share a number of mechanisms of neuronal damage. In both cases the balance between neurodestruction and neuroprotection appears modulated by the function of the adaptive immune system. MS is a chronic inflammatory disease of the central nervous system (CNS), leading to permanent disability. It seems certain that an autoimmune response directed against the CNS is central to the pathogenesis of the disease. While these CNS-specific T cells are activated in MS patients, they are inactive and naive in healthy. Therefore it is believed that an activation of autoreactive T cells by cross-reactivity with pathogens occurs outside of the CNS. In consequence T cells express adhesion molecules and proteinases which enable them to cross the blood-brain barrier. In stroke, however, the blood-brain barrier is disturbed in its integrity caused by the decreased blood flow. Cells can freely migrate from the periphery into the brain. CNS autoreactive cells from the periphery can be activated within the CNS and thus contribute to further tissue damage. While the local autoimmune response remains temporary in stroked brains, it is chronically destroyed in MS. The differences between the underlying mechanisms are not understood. This thesis investigated T cell responses in Multiple Sclerosis in response to the therapeutics Mitoxantrone and IFN-b. The induction of a TH1 to TH2 cytokine response appears to be a shared mechanism of action between both therapeutic agents. Primarily the post stroke immune response was investigated. Patients developed a stroke induced immune suppression characterized by monocytic dysfunction and lymphocytopenia explaining the high frequency of post stroke infections. Moreover early post stroke predictors of subsequent infections, like the CD4+ T cell count, were identified. The T cell response of stroke patients appeared primed to proinflammation and unsuppressed after mitogen stimulation. A detailed understanding of post stroke immune alterations may offer new avenues of intervention to improve the clinical fate of stroke victims. In addition, such knowledge could also further our understanding of Multiple Sclerosis, because, while increasing the infection risk, the dampening of the immune system could have an important protective function, if it limits autoimmune brain damage triggered by the massive release of brain antigens during stroke. If these two pathways could be modulated separately it would create the opportunity to develop distinct therapeutic approaches that inhibit autoimmunity and strengthen antibacterial defenses. To further delineate these mechanisms it is crucial to investigate the role of the innate immune system as compared to the adaptive immune system in stroke induced immune suppression.
Background: Newborns are prone to infections, which are independent predictors of neonatal mortality and morbidity. Neutrophil extracellular traps (NETs) are structures composed of chromatin and antimicrobial molecules that capture and kill pathogens. NETs may play an important role in the innate immune system and, thus, might be associated with impaired neonatal immune function. Objectives: This study aimed to compare NET formation between term neonates and healthy adults. We additionally investigated the effects of gestational age, birth weight, mode of delivery, gender, and perinatal infections. Methods: We collected cord blood from 57 term infants (mean gestational age, 39.1 weeks) and 9 late preterm infants (35 weeks), and peripheral blood from 18 healthy adult donors. Neutrophils were isolated, and then NET formation was induced using three different stimulants: N-formylmethionine-leucyl-phenylalanine, phorbol 12-myristate 13-acetate (PMA), or lipopolysaccharide. NETs were immunohistochemically stained and analyzed with regard to NET percentage and NET area. Results: With all three stimuli, healthy term infants showed a lower NET percentage than the adult control group (p < 0.0001 each). The groups also differed in NET area, but the significance level was lower. Following PMA stimulation, we observed greater reductions in NET percentage and NET area in preterm than term infants. Conclusions: The lower NET formation observed in term infants compared to adults likely contributes to the reduced neonatal immune response. NET formation appeared to be even further decreased in late preterm neonates. There remains a need for further investigations of NET formation in more immature preterm infants.
Background: Gastrointestinal hormones (GIHs) are crucial for the regulation of a variety of physiological functions and have been linked to hunger, satiety, and appetite control. Thus, they might constitute meaningful biomarkers in longitudinal and interventional studies on eating behavior and body weight control. However, little is known about the physiological levels of GIHs, their intra-individual stability over time, and their interaction with other metabolic and lifestyle-related parameters. Therefore, the aim of this pilot study is to investigate the intra-individual stability of GIHs in normal-weight adults over time. Methods: Plasma concentrations of ghrelin, leptin, GLP-1 (glucagon-like-peptide), and PP (pancreatic polypeptide) were assessed by enzyme-linked immunosorbent assay (ELISA) in 17 normal-weight, healthy adults in a longitudinal design at baseline and at follow-up six months later. The reliability of the measurements was estimated using intra-class correlation (ICC). In a second step, we considered the stability of GIH levels after controlling for changes in blood glucose and hemoglobin A1 (HbA1c) as well as self-reported physical activity and dietary habits. Results: We found excellent reliability for ghrelin, good reliability for GLP1 and PP, and moderate reliability for leptin. After considering glucose, HbA1c, physical activity, and dietary habits as co-variates, the reliability of ghrelin, GLP1, and PP did not change significantly; the reliability of leptin changed to poor reliability. Conclusions: The GIHs ghrelin, GLP1, and PP demonstrated good to excellent test–retest reliability in healthy individuals, a finding that was not modified after adjusting for glucose control, physical activity, or dietary habits. Leptin showed only moderate to poor reliability, which might be linked to weight fluctuations, albeit small, between baseline and follow-up assessment in our study sample. Together, these findings support that ghrelin, GLP1, and PP might be further examined as biomarkers in studies on weight control, with GLP1 and PP serving as anorexic markers and ghrelin as an orexigenic marker. Additional reliability studies in obese individuals are necessary to verify or refute our findings for this cohort.
Background: Stroke patients are at risk of acquiring secondary infections due to stroke-induced immune suppression (SIIS). Immunosuppressive cells comprise myeloid-derived suppressor cells (MDSCs) and immunosuppressive interleukin 10 (IL-10)-producing monocytes. MDSCs represent a small but heterogeneous population of monocytic, polymorphonuclear (or granulocytic), and early progenitor cells (“early” MDSC), which can expand extensively in pathophysiological conditions. MDSCs have been shown to exert strong immune-suppressive effects. The role of IL-10-producing immunosuppressive monocytes after stroke has not been investigated, but monocytes are impaired in oxidative burst and downregulate human leukocyte antigen—DR isotype (HLA-DR) on the cell surface.
Objectives: The objective of this work was to investigate the regulation and function of MDSCs as well as the immunosuppressive IL-10-producing monocytes in experimental and human stroke.
Methods: This longitudinal, monocentric, non-interventional prospective explorative study used multicolor flow cytometry to identify MDSC subpopulations and IL-10 expression in monocytes in the peripheral blood of 19 healthy controls and 27 patients on days 1, 3, and 5 post-stroke. Quantification of intracellular STAT3p and Arginase-1 by geometric mean fluorescence intensity was used to assess the functionality of MDSCs. In experimental stroke induced by electrocoagulation in middle-aged mice, monocytic (CD11b+Ly6G−Ly6Chigh) and polymorphonuclear (CD11b+Ly6G+Ly6Clow) MDSCs in the spleen were analyzed by flow cytometry.
Results: Compared to the controls, stroke patients showed a relative increase in monocytic MDSCs (percentage of CD11b+ cells) in whole blood without evidence for an altered function. The other MDSC subgroups did not differ from the control. Also, in experimental stroke, monocytic, and in addition, polymorphonuclear MDSCs were increased. The numbers of IL-10-positive monocytes did not differ between the patients and controls. However, we provide a new insight into monocytic function post-stroke since we can report that a differential regulation of HLA-DR and PD-L1 was found depending on the IL-10 production of monocytes. IL-10-positive monocytes are more activated post-stroke, as indicated by their increased HLA-DR expression.
Conclusions: MDSC and IL-10+ monocytes can induce immunosuppression within days after stroke.
The release of DNA by cells during extracellular trap (ET) formation is a defense function of neutrophils and monocytes. Neutrophil ET (NET) formation in term infants is reduced compared to adults. Objective: The aim was to quantify NET and monocyte ET (MET) release and the respective key enzymes myeloperoxidase (MPO) and neutrophil elastase (NE) in preterm infants. In this prospective explorative study, ET induction was stimulated by N-formylmethionine-leucyl-phenylalanine (fMLP), phorbol 12-myristate 13-acetate (PMA), lipopolysaccharide (LPS), and lipoteichoic acid (LTA) in the cord blood of preterm infants (n = 55, 23–36 weeks) compared to term infants and adults. METs were quantified by microscopy, and NETs by microscopy and flow cytometry. We also determined the MPO levels within NETs and the intracellular concentrations of NE and MPO in neutrophils. The percentage of neutrophils releasing ET was significantly reduced for preterm infants compared to adults for all stimulants, and with a 68% further reduction for PMA compared to term infants (p = 0.0141). The NET area was not reduced except for when fMLP was administered. The amount of MPO in NET-producing cells was reduced in preterm infants compared to term infants. For preterm infants, but not term infants, the percentage of monocytes releasing ETs was significantly reduced compared to healthy adults for LTA and LPS stimulation. Conclusion: In preterm infants, ETs are measurable parts of the innate immune system, but are released in a reduced percentage of cells compared to adults.