Dannielle Zierath

Autoimmune Responses to the Brain After Stroke Are Associated With Worse Outcome

Background and Purpose— Immune responses to brain antigens occur after stroke, and experimental studies show that the likelihood of developing a detrimental autoimmune response to these antigens is increased by systemic inflammation at the time of stroke. The aim of this study was to determine if patients who developed infection in the poststroke period would be similarly predisposed to develop autoimmune responses to central nervous system antigens. Methods— We enrolled 114 patients within 72 hours of ischemic stroke. Clinical and demographic data were obtained, and cellular immune responses to a panel of central nervous system antigens were assessed during the initial week and again at Day 90. Outcome was assessed using the modified Rankin Scale. Results— Patients who developed an infection, especially pneumonia, in the 15 days after stroke were more likely to evidence a Th1(+) response to myelin basic protein and glial fibrillary acidic protein (P=0.019 and P=0.039, respectively) at 90 days after stroke. Further, more robust Th1 responses to myelin basic protein at 90 days were associated with a decreased likelihood of good outcome, even after adjusting for baseline stroke severity and patient age (OR, 0.477; 95% CI, 0.244 to 0.935; P=0.031). Conclusions— This study demonstrates that immune responses to brain antigens occur after stroke. Although these responses are likely to be an epiphenomenon of ischemic brain injury, the response to myelin basic protein appears to have clinical consequences. The potential role of postischemic autoimmune-mediated brain injury deserves further investigation.

Severe Stroke Induces Long-Lasting Alterations of High-Mobility Group Box 1

Background and Purpose— The signals that initiate the poststroke inflammatory response are unknown. High-mobility group box (HMGB) 1 protein is a nuclear protein that is passively released from necrotic tissue and is able to activate leukocytes, which in turn secrete HMGB1. HMGB1 is also able to activate antigen-presenting cells and therefore stands at the crossroads of innate and adaptive immunity. Methods— Plasma HMGB1 concentrations were determined at multiple time points after ischemic stroke (N=110) and correlated to stroke severity and biomarkers of inflammation. The relationships between HMGB1, stroke outcome, and autoimmune responses to brain antigens were also assessed. Results— Stroke resulted in an increase in HMGB1 that persisted for 30 days. Plasma HMGB1 was correlated with the number of circulating leukocytes but was not predictive of either stroke outcome or the development of autoimmune responses to brain antigens. Patients with a TH1(+) response to myelin basic protein at 90 days after stroke, however, had higher plasma HMGB1. Conclusions— HMGB1 appears to be involved in the postischemic inflammatory response, but it remains unclear whether HMGB1 initiates this response or merely reflects activation of leukocytes by another signal.

Long term immunologic consequences of experimental stroke and mucosal tolerance

BackgroundAn inflammatory insult following middle cerebral artery occlusion (MCAO) is associated with a predisposition to develop a deleterious autoimmune response to the brain antigen myelin basic protein (MBP). Induction of immunologic tolerance to brain antigens prior to MCAO prevents this deleterious autoimmune response and is associated with better functional outcome early after stroke. In this study, we sought to determine the long term immunologic consequences of experimental stroke and induction of mucosal tolerance.MethodsMale Lewis rats were tolerized to MBP or ovalbumin (OVA) by intranasal administration prior to MCAO and administration of lipopolysaccharide (LPS). Neurological outcome was assessed at set points after MCAO and animals sacrificed at 3 months; the immune response to MBP in brain and spleen was determined using ELISPOT assay and degree of cellular inflammatory brain infiltrate assessed by immunocytochemistry.ResultsAnimals that developed a pro-inflammatory (TH 1) response to MBP experienced worse outcome, while those that developed a regulatory response (TREG) experienced better outcome. A TREG response in spleen was also associated with decreased inflammation and an increase in the number of FoxP3 positive cells in brain. In this study, tolerization to MBP prior to MCAO was associated with a tendency to develop a TH 1 response to MBP by 3 months after MCAO.ConclusionThese data show that induction of immunological tolerance to MBP is associated with improved outcome after stroke. This study, however, raises concern about the potential for inadvertent induction of detrimental autoimmunity through mucosal administration of antigen.

Higher Plasma Fractalkine Is Associated With Better 6-Month Outcome From Ischemic Stroke

Background and Purpose— Fractalkine (CX3CL1) is a unique chemokine that is constitutively expressed on neurons where it serves as an adhesion molecule for lymphocytes and monocytes. CX3CL1 may also be cleaved from the surface of these cells and enter the circulation to act as a traditional chemokine. CX3CL1 could thus influence the inflammatory response after stroke. We hypothesized that patients with higher plasma CX3CL1 after stroke would have a more robust inflammatory response and experience worse outcome. Methods— Plasma CX3CL1 concentrations were assessed in 85 patients who were part of a larger study evaluating immune responses after ischemic stroke; CX3CL1 values were available from Day 1 to Day 180 after stroke onset. CX3CL1 was correlated to measures of inflammation and its effect on outcome assessed. Results— At 1 day after stroke, CX3CL1 was lower in patients with severe strokes. At 180 days after stroke, CX3CL1 concentrations were lower in patients with poor outcome. The association of CX3CL1 and outcome at 180 days was independent of initial stroke severity. Plasma CX3CL1 at 180 days was inversely associated with systemic markers of inflammation, including white blood cell counts and high-sensitivity C-reactive protein. Conclusions— In contrast to our original hypothesis, lower concentrations of CX3CL1 are associated with worse stroke outcome. In light of recent studies suggesting an immunomodulatory and neuroprotective role for CX3CL1 in a variety of neurodegenerative diseases, a therapeutic role for CX3CL1 in stroke recovery should be considered.

Plasma α-Melanocyte Stimulating Hormone Predicts Outcome in Ischemic Stroke

Background and Purpose— &agr;-Melanocyte stimulating hormone (&agr;-MSH) is an endogenously produced neuropeptide derived from the same precursor as adrenocorticotropic hormone. &agr;-MSH has profound immunomodulatory properties and may also be neuroprotective. Nothing is known about &agr;-MSH and changes in its plasma concentrations in patients with acute ischemic stroke. Methods— In this prospective observational study, plasma concentrations of &agr;-MSH, adrenocorticotropic hormone, cortisol, and interleukin 6 were assessed longitudinally over the course of 1 year after stroke onset in 111 patients. Logistic regression was used to the effect of initial plasma &agr;-MSH, adrenocorticotropic hormone, cortisol, and interleukin 6 on long-term outcome. Results— There was an early decrease in plasma &agr;-MSH in patients with severe stroke (National Institutes of Health Stroke Scale ≥17) that normalized over the course of the year; these same patients evidenced elevations in plasma cortisol and interleukin 6. Higher initial plasma &agr;-MSH, but not adrenocorticotropic hormone, cortisol, or interleukin 6, was independently predictive of good long-term outcome. Conclusions— This research is the first to study endogenous changes in plasma &agr;-MSH after stroke. The independent effect of early plasma &agr;-MSH on stroke outcome, as well as a growing body of experimental data demonstrating improved stroke outcome with exogenous &agr;-MSH administration, suggests a potential therapeutic role for &agr;-MSH in the treatment of stroke.

α-MSH: a potential neuroprotective and immunomodulatory agent for the treatment of stroke.

Alpha-melanocyte-stimulating hormone (MSH) is a neuropeptide with profound immunomodulatory properties; we evaluated the effects of α-MSH on stroke outcome and its ability to modulate the postischemic immune response. In Lewis rats subjected to 3 hours of middle cerebral artery occlusion (MCAO), plasma concentrations of α-MSH rapidly decreased and returned to baseline over the course of days. Exogenous administration of α-MSH (100 or 500 μg/kg) improved 24 hour outcome in animals subjected to 2 hours MCAO; α-MSH 500 μg/kg also decreased infarct volume at this time point. Both doses of α-MSH were ineffective in improving outcome or decreasing infarct volume in animals subjected to 3 hours MCAO. The splenocyte response to phytohemagglutin in animals treated with α-MSH was attenuated at 24 hours after MCAO. At 1 month after MCAO, treatment with α-MSH 500 μg/kg at the time of stoke was associated with a decrease in TH1 response to myelin basic protein (MBP) in animals subjected to 2 hours MCAO, although treatment was not associated with improved outcome at this time point. Given the early benefits of α-MSH treatment and its effect on immunologic outcome, further studies to evaluate the utility of α-MSH for the treatment of cerebral ischemia are warranted.

Poststroke Fatigue: Hints to a Biological Mechanism

BACKGROUND Poststroke fatigue (PSF) is common, but the biological basis of this fatigue is unknown. We explored the possibility that PSF is related to systemic inflammation by investigating polymorphisms in 2 genes that affect the immune response. METHODS In a substudy of a larger trial that evaluated the role of the immune response on stroke outcome, fatigue was assessed at 30, 90, 180, and 365 days after ischemic stroke using the Fatigue Assessment Scale. Subjects were genotyped for 3 single nucleotide polymorphisms, one in the interleukin-1 receptor antagonist gene (IL1RN; rs4251961, a T/C substitution) and two in the in toll-like receptor-4 (TLR4) gene (1063 A/G [Asp299Gly] rs4986790 and 1363 C/T [Thr399Ile] rs4986791). RESULTS Of the 39 participants, 22 (56%) endorsed fatigue during the study. The degree of fatigue was remarkably constant over time and independent of stroke outcome. The C allele of the rs4251961 single nucleotide polymorphism (SNP) in IL1RN was associated with self-reported fatigue (P = .03), whereas the cosegregating polymorphisms in TLR4 were associated with lower levels of fatigue (P= .04). CONCLUSIONS SNPs in 2 genes with opposing effects on inflammatory immune responses were significantly, but differentially, associated with PSF. These findings suggest a direct link between immune signaling dysregulation and PSF.

The immunologic profile of adoptively transferred lymphocytes influences stroke outcome of recipients

Animals that have myelin basic protein (MBP) specific lymphocytes with a Th1(+) phenotype have worse stroke outcome than those that do not. Whether these MBP specific cells contribute to worsened outcome or are merely a consequence of worse outcome is unclear. In these experiments, lymphocytes were obtained from donor animals one month after stroke and transferred to naïve recipient animals at the time of cerebral ischemia. The MBP specific phenotype of donor cells was determined prior to transfer. Animals that received either MBP specific Th1(+) or Th17(+) cells experienced worse neurological outcome, and the degree of impairment correlated with the robustness of MBP specific Th1(+) and Th17(+) responses. These data demonstrate that the immunologic phenotype of antigen specific lymphocytes influences stroke outcome.

Promiscuity of autoimmune responses to MBP after stroke

In this study we examined Th1 and Th17 immune responses to rat myelin basic protein (MBP), bovine MBP, human MBP, MBP 68-86, MBP 63-81 and ovalbumin in Lewis rats to determine which MBP antigen is recognized following ischemic brain injury. Responses were compared to animals immunized to rat MBP. Data show that immune responses following immunization with rat MBP are promiscuous with cross reaction to MBP from other species. After stroke, few animals develop Th1 or Th17 responses to MBP, but when those responses occur, especially Th1 responses to rat MBP in the brain, they are predictive of worse stroke outcome.

Anamnestic Recall of Stroke-Related Deficits. An Animal Model

Background and Purpose— Anamnestic recall of stroke-related deficits is a common clinical observation, especially during periods of systemic infection. The pathophysiology of this transient re-emergence of neurological dysfunction is unknown. Methods— Male Lewis rats underwent 3 hours middle cerebral artery occlusion and were treated with lipopolysaccharide or saline at the time of reperfusion. The delayed-type hypersensitivity (DTH) response to myelin basic protein was examined 28 days after middle cerebral artery occlusion. Changes in behavioral outcomes were assessed after DTH testing and repeat administration of lipopolysaccharide or saline at 34 days. At the time of euthanasia (36 days), the immunologic response of splenocytes to myelin basic protein, neuron-specific enolase, and proteolipid protein was determined by enzyme-linked immunospot assay and the number of lymphocytes in the brain determined by immunocytochemistry. Results— Animals treated with lipopolysaccharide at middle cerebral artery occlusion had a greater DTH response to myelin basic protein than animals treated with saline. Among those animals that had fully recovered on a given behavioral test before DTH testing, those treated with lipopolysaccharide at middle cerebral artery occlusion displayed more neurological deterioration after DTH testing and had more CD8+ lymphocytes within the ischemic core of the brain. Furthermore, the Th1 immune response to brain antigens in the spleen was more robust among those animals that deteriorated after DTH testing and there were more CD4+ lymphocytes in the penumbral region of animals with a Th1 response to myelin basic protein. Conclusions— Our data suggest that an immune response to the brain contributes to the phenomenon of anamnestic recall of stroke-related deficits after an infection. The contribution of the immune response to this phenomenon deserves further investigation.