Christian Meisel

Stroke-induced Immunodeficiency Promotes Spontaneous Bacterial Infections and Is Mediated by Sympathetic Activation Reversal by Poststroke T Helper Cell Type 1–like Immunostimulation

Infections are a leading cause of death in stroke patients. In a mouse model of focal cerebral ischemia, we tested the hypothesis that a stroke-induced immunodeficiency increases the susceptibility to bacterial infections. 3 d after ischemia, all animals developed spontaneous septicemia and pneumonia. Stroke induced an extensive apoptotic loss of lymphocytes and a shift from T helper cell (Th)1 to Th2 cytokine production. Adoptive transfer of T and natural killer cells from wild-type mice, but not from interferon (IFN)-γ–deficient mice, or administration of IFN-γ at day 1 after stroke greatly decreased the bacterial burden. Importantly, the defective IFN-γ response and the occurrence of bacterial infections were prevented by blocking the sympathetic nervous system but not the hypothalamo-pituitary-adrenal axis. Furthermore, administration of the β-adrenoreceptor blocker propranolol drastically reduced mortality after stroke. These data suggest that a catecholamine-mediated defect in early lymphocyte activation is the key factor in the impaired antibacterial immune response after stroke.

Central nervous system injury-induced immune deficiency syndrome

Infections are a leading cause of morbidity and mortality in patients with acute CNS injury. It has recently become clear that CNS injury significantly increases susceptibility to infection by brain-specific mechanisms: CNS injury induces a disturbance of the normally well balanced interplay between the immune system and the CNS. As a result, CNS injury leads to secondary immunodeficiency — CNS injury-induced immunodepression (CIDS) — and infection. CIDS might serve as a model for the study of the mechanisms and mediators of brain control over immunity. More importantly, understanding CIDS will allow us to work on developing effective therapeutic strategies, with which the outcome after CNS damage by a host of diseases could be improved by eliminating a major determinant of poor recovery.

Stroke-Induced Immunodepression Experimental Evidence and Clinical Relevance

Stroke affects the normally well-balanced interplay of the 2 supersystems: the nervous and the immune system. Recent research elucidated some of the involved signals and mechanisms and, importantly, was able to demonstrate that brain-immune interactions are highly relevant for functional outcome after stroke. Immunodepression after stroke increases the susceptibility to infection, the most relevant complication in stroke patients. However, immunodepression after stroke may also have beneficial effects, for example, by suppressing autoaggressive responses during lesion-induced exposure of central nervous system-specific antigens to the immune system. Thus, before immunomodulatory therapy can be applied to stroke patients, we need to understand better the interaction of brain and immune system after focal cerebral ischemia. Until then, anticipating an important consequence of stroke-induced immunodepression, bacterial infection, preventive antibiotic strategies have been proposed. In mouse experiments, preventive antibiotic treatment dramatically improves mortality and outcome. Results of clinical studies on this issue are contradictory at present, and larger trials are needed to settle the question whether (and which) stroke patients should be preventively treated. Nevertheless, clinical evidence is emerging demonstrating that stroke-induced immunodepression in humans not only exists, but has very similar features to those characterized in rodent experiments.

Preventive Antibacterial Therapy in Acute Ischemic Stroke: A Randomized Controlled Trial

Background Pneumonia is a major risk factor of death after acute stroke. In a mouse model, preventive antibacterial therapy with moxifloxacin not only prevents the development of post-stroke infections, it also reduces mortality, and improves neurological outcome significantly. In this study we investigate whether this approach is effective in stroke patients. Methods Preventive ANtibacterial THERapy in acute Ischemic Stroke (PANTHERIS) is a randomized, double-blind, placebo-controlled trial in 80 patients with severe, non-lacunar, ischemic stroke (NIHSS>11) in the middle cerebral artery (MCA) territory. Patients received either intravenous moxifloxacin (400 mg daily) or placebo for 5 days starting within 36 hours after stroke onset. Primary endpoint was infection within 11 days. Secondary endpoints included neurological outcome, survival, development of stroke-induced immunodepression, and induction of bacterial resistance. Findings On intention-to treat analysis (79 patients), the infection rate at day 11 in the moxifloxacin treated group was 15.4% compared to 32.5% in the placebo treated group (p = 0.114). On per protocol analysis (n = 66), moxifloxacin significantly reduced infection rate from 41.9% to 17.1% (p = 0.032). Stroke associated infections were associated with a lower survival rate. In this study, neurological outcome and survival were not significantly influenced by treatment with moxifloxacin. Frequency of fluoroquinolone resistance in both treatment groups did not differ. On logistic regression analysis, treatment arm as well as the interaction between treatment arm and monocytic HLA-DR expression (a marker for immunodepression) at day 1 after stroke onset was independently and highly predictive for post-stroke infections. Interpretation PANTHERIS suggests that preventive administration of moxifloxacin is superior in reducing infections after severe non-lacunar ischemic stroke compared to placebo. In addition, the results emphasize the pivotal role of immunodepression in developing post-stroke infections. Trial Registration Controlled-Trials.com ISRCTN74386719

Stroke-induced immunodepression and post-stroke infections: Lessons from the preventive antibacterial therapy in stroke trial

UNLABELLED Infections are a leading cause of death in patients with acute CNS injury such as stroke. Recent experimental evidence indicated that stroke leads to suppression of innate and adaptive peripheral immune responses which predisposes to infection. However, less is known on phenotypic and functional immune alterations in correlation with the occurrence of infectious complications in patients with acute stroke. EXPERIMENTAL PROCEDURES In the recently completed randomized, double blind, placebo-controlled Preventive Antibacterial Therapy in Stroke (PANTHERIS) trial on the efficacy of short-term antibacterial therapy to prevent the development of post-stroke infections, we assessed longitudinal changes in lymphocyte subpopulations and mitogen-induced lymphocytic interferon gamma (IFN)-gamma production using flow cytometry in 80 patients with acute severe stroke at days 1, 3, 8, 90 and 180 after clinical onset. Plasma interleukin (IL)-6 and IL-10 concentration as well as urinary levels of norepinephrine and cortisol was assessed within the first 8 days after stroke. Patients of the placebo and verum (moxifloxacin) treatment groups who did or did not develop infections within 11 days after stroke were compared to identify immunological changes associated with the occurrence of post-stroke infections. RESULTS Rapid T-lymphopenia and long-lasting suppression of lymphocytic IFN-gamma production were observed in all stroke patients. Patients of the placebo group who developed infections showed a trend toward greater decline of CD4+ Th cell counts and higher urinary levels of norepinephrine early after stroke than patients without infections. Onset of infections was accompanied with higher plasma IL-6 levels in the placebo group but not in the moxifloxacin group. In addition, an early rise in plasma IL-10 was detected in patients who developed infections despite preventive antibacterial treatment. CONCLUSION A rapid loss and functional deactivation of T cells are common changes in stroke patients consistent with immunodepression after brain ischemia. A stronger decrease in cellular immune responses and an increased sympathetic activity after stroke are associated with a higher risk of infections. Increased plasma levels of the anti-inflammatory cytokine IL-10 early after stroke may identify patients who will not respond to preventive antibacterial therapy with moxifloxacin.

Cellular immunodepression preceding infectious complications after acute ischemic stroke in humans

Background: We have recently shown that ischemic stroke causes a stress-mediator-induced long-lasting immunodepressive state in mice. Methods: Using head magnetic resonance imaging and standardized immunoassays, we prospectively investigated whether poststroke immunodepression is also seen in humans. Results: Compared to healthy volunteers (n = 30), a rapid depression of lymphocyte counts and a functional deactivation of monocytes and T helper type 1 cells was observed in acute stroke patients (SP; n = 40). Immunodepression was more pronounced in patients with severe clinical deficit or large infarction. On admission the combination of monocytic tumor necrosis factor α release ex vivo and the National Institute of Health Stroke Scale score were the best predictors for nosocomial infection, preferentially affecting older SP. Conclusion: Our data provide evidence for an immediate suppression of cell-mediated immune responses after ischemic stroke in humans.

Stroke Propagates Bacterial Aspiration to Pneumonia in a Model of Cerebral Ischemia

Background and Purpose— Bacterial pneumonia is the most common cause of death in patients sustaining acute stroke and is believed to result from an increased aspiration. Recently, stroke-induced immunodeficiency was described in a mouse model of cerebral ischemia, which is primarily caused by overactivation of sympathetic nervous system. We tested if stroke-induced immunodeficiency increases the risk of pneumonia after aspiration in a newly developed model of poststroke pneumonia. Methods— Experimental stroke in mice was induced by occlusion of the middle cerebral artery (MCAO) for 60 minutes. Aspiration pneumonia was induced by intranasal application of 20 &mgr;L of a defined suspension of Streptococcus pneumoniae in phosphate-buffered saline 4 or 14 days after MCAO. Treatment comprised moxifloxacin (100 mg/kg body weight, six times every 2 hours after operation) or propranolol (30 mg/kg body weight, immediately before as well as 4 and 8 hours after MCAO). Readout was lung histology and bacterial counts in lung and blood. Results— Nasal inoculation of only 200 colony-forming units of S pneumoniae caused severe pneumonia and bacteremia after experimental stroke, whereas 200 000 colony-forming units are needed to induce comparable disease in sham animals. Aspiration pneumonia in stroke animals outlasted acute stroke state but was preventable by β-adrenoreceptor blockade. Conclusions— Experimental stroke propagates bacterial aspiration from harmless intranasal colonization to harmful pneumonia. Prevention of infections by β-adrenoreceptor blockade suggests that immunodepression by sympathetic hyperactivity is essential for progression of bacterial aspiration to pneumonia.

Preventive Antibacterial Treatment Improves the General Medical and Neurological Outcome in a Mouse Model of Stroke

Background and Purpose— Epidemiological studies have demonstrated a high incidence of infections after severe stroke and their prominent role in morbidity and mortality in stroke patients. In a mouse model, it has been shown recently that stroke is coupled with severe and long-lasting immunosuppression, which is responsible for the development of spontaneous systemic infections. Here, we investigated in the same model the effects of preventive antibiotic treatment on survival and functional outcome of experimental stroke. Methods— Mice were subjected to experimental stroke by occlusion of the middle cerebral artery (MCAO) for 60 minutes. A group of mice received moxifloxacin (6×100 mg/kg body weight every 2 hours over 12 hours) either immediately or 12 hours after MCAO. Control animals received the vector only. Behavior, neurological deficit, fever, survival, and body weight were monitored over 14 days. In a subgroup, infarct volume was measured 4 days after MCAO. Microbiological assessment was based on cultures of lung tissue, blood, and feces of animals 3 days after stroke. For a dose-response study, moxifloxacin was given immediately after MCAO in different doses and at different time points. Results— Microbiological analyses of blood and lung tissue demonstrated high bacterial burden, mainly Escherichia coli, 3 days after stroke. Accordingly, we observed clinical and histological signs of septicemia and pneumonia. Moxifloxacin prevented the development of infections and fever, significantly reduced mortality, and improved neurological outcome. Conclusions— Preventive antibiotic treatment may be an important new therapeutical approach to improve outcome in patients with severe stroke.

Regulation and Function of T1/ST2 Expression on CD4+ T Cells: Induction of Type 2 Cytokine Production by T1/ST2 Cross-Linking

The orphan receptor T1/ST2, a member of the IL-1R family, is preferentially expressed on the surface of murine Th2 cells. In this study, we analyzed the kinetics and function of T1/ST2 expression on Th2 cells in vitro. Whereas naive CD4+ cells did not express T1/ST2, most CD4+ cells became T1/ST2+ upon repeated antigenic stimulation under Th2-polarizing conditions. Flow cytometric analyses revealed that the kinetics of T1/ST2 expression on Th2 cells was delayed compared with the kinetics of type 2 cytokine production. Exogenous IL-6, IL-5, IL-1, and TNF-α enhanced the expression of T1/ST2 on Th2 cells, and IL-6 was by far most effective in this regard. However, the expression of T1/ST2 did not depend on the presence of IL-6 and was also detected in IL-6-deficient mice. Most important, cross-linking of T1/ST2 provided a costimulatory signal for Th2 but not Th1 cells and directly induced proliferation and type 2 cytokine production. Thus, T1/ST2 is not only a Th2 cell marker but also plays an important role in the activation of Th2 cells.

Terminally Differentiated CD8+ T Cells Negatively Affect Bone Regeneration in Humans

A subset of T cells inhibits bone regeneration in humans. No Bones About It Sticks and stones may break your bones, but immune cells will not hurt you, at least if Reinke et al. have anything to say about it. The immune system seems to have a hand in everything these days, and bone repair is no exception. T cells have been implicated in modulating bone fracture repair, even in the absence of infection. Reinke et al. take these studies into patients and find that delayed fracture healing correlated with a subset of T cells—terminally differentiated effector memory CD8+ T (TEMRA) cells. The authors examined the number of CD8+ TEMRA cells over time and found that the difference in CD8+ TEMRA cell number in patients with delayed healing reflected the individual’s immune profile, or lifelong response to infection, rather than a more acute, fracture-related event. They specifically found these cells in fracture hematoma, one of the earliest stages of fracture healing. They then took these studies into mice and found that the absence of CD8+ T cells improved bone regeneration, whereas adding CD8+ T cells impaired fracture healing. This mechanistic link supported their association in patients and suggests that these CD8+ TEMRA cells may be targeted or serve as markers for intervention in patients with delayed bone fracture healing. There is growing evidence that adaptive immunity contributes to endogenous regeneration processes: For example, endogenous bone fracture repair is modulated by T cells even in the absence of infection. Because delayed or incomplete fracture healing is associated with poor long-term outcomes and high socioeconomic costs, we investigated the relationship between an individual’s immune reactivity and healing outcome. Our study revealed that delayed fracture healing significantly correlated with enhanced levels of terminally differentiated CD8+ effector memory T (TEMRA) cells (CD3+CD8+CD11a++CD28−CD57+ T cells) in peripheral blood. This difference was long lasting, reflecting rather the individual’s immune profile in response to lifelong antigen exposure than a post-fracture reaction. Moreover, CD8+ TEMRA cells were enriched in fracture hematoma; these cells were the major producers of interferon-γ/tumor necrosis factor–α, which inhibit osteogenic differentiation and survival of human mesenchymal stromal cells. Accordingly, depletion of CD8+ T cells in a mouse osteotomy model resulted in enhanced endogenous fracture regeneration, whereas a transfer of CD8+ T cells impaired the healing process. Our data demonstrate the high impact of the individual adaptive immune profile on endogenous bone regeneration. Quantification of CD8+ TEMRA cells represents a potential marker for the prognosis of the healing outcome and opens new opportunities for early and targeted intervention strategies.