T. Bucky Jones

Rats and mice exhibit distinct inflammatory reactions after spinal cord injury

Spinal contusion pathology in rats and mice is distinct. Cystic cavities form at the impact site in rats while a dense connective tissue matrix occupies the injury site in mice. Because inflammatory cells coordinate mechanisms of tissue injury and repair, we evaluated whether the unique anatomical presentation in spinally injured rats and mice is associated with a species‐specific inflammatory response. Immunohistochemistry was used to compare the leukocytic infiltrate between rats and mice. Microglia/macrophage reactions were similar between species; however, the onset and magnitude of lymphocyte and dendritic cell (DC) infiltration were markedly different. In rats, T‐cell numbers were highest between 3 and 7 days postinjury and declined by 50% over the next 3 weeks. In mice, significant T‐cell entry was not evident until 14 days postinjury, with T‐cell numbers doubling between 2 and 6 weeks. Dendritic cell influx paralleled T‐cell infiltration in rats but was absent in mouse spinal cord. De novo expression of major histocompatability class II molecules was increased in both species but to a greater extent in mice. Unique to mice were cells that resembled lymphocytes but did not express lymphocyte‐specific markers. These cells extended from blood vessels within the fibrotic tissue matrix and expressed fibronectin, collagen I, CD11b, CD34, CD13, and CD45. This phenotype is characteristic of fibrocytes, specialized blood‐borne cells involved in wound healing and immunity. Thus, species‐specific neuroinflammation may contribute to the formation of distinct tissue environments at the site of spinal cord injury in mice and rats. J. Comp. Neurol. 462:223–240, 2003.

Manipulating neuroinflammatory reactions in the injured spinal cord: back to basics

Recruitment of inflammatory leukocytes to the injured spinal cord is a physiological response that is associated with the production of cytokines and proteinases that are involved in host defense and wound repair. Cells in the spinal cord are mainly post-mitotic and tissue regeneration is poor; thus, these inflammatory mediators can exacerbate the damage to spared tissue and thereby impair spontaneous functional recovery. Although several aspects of immune function might benefit the CNS, experimental studies indicate that acute neuroinflammation aggravates tissue injury. Until the timing and nature of the molecular signals that govern leukocyte recruitment and activation after spinal injury are defined, clinical therapies designed to boost immune cell function should be avoided.

Passive or Active Immunization with Myelin Basic Protein Impairs Neurological Function and Exacerbates Neuropathology after Spinal Cord Injury in Rats

Myelin-reactive T-cells are activated by traumatic spinal cord injury (SCI) in rodents and humans. Despite the historical association of these cells with experimental and clinical neuropathology, recent data suggest a neuroprotective role for myelin-reactive T-cells. Because of the biological and therapeutic implications of these findings, we attempted to reproduce the original neuroprotective vaccine protocols in a model of rat SCI. Specifically, MBP-reactive T-cell function was enhanced in SCI rats via passive or active immunization. Locomotor function was assessed using a standardized locomotor rating scale (Basso–Beattie–Bresnahan scale) and was correlated with myelin and axon sparing. The functional and anatomical integrity of the rubrospinal pathway also was analyzed using the inclined plane test and anatomical tract tracing. MBP-immunized rats exhibited varying degrees of functional impairment, exacerbated lesion pathology, greater rubrospinal neuron loss, increased intraspinal T-cell accumulation, and enhanced macrophage activation relative to SCI control groups. These data are consistent with the conventional view of myelin-reactive T-cells as pathological effector cells.

Molecular Control of Physiological and Pathological T-Cell Recruitment after Mouse Spinal Cord Injury

The intraspinal cues that orchestrate T-cell migration and activation after spinal contusion injury were characterized using B10.PL (wild-type) and transgenic (Tg) mice with a T-cell repertoire biased toward recognition of myelin basic protein (MBP). Previously, we showed that these strains exhibit distinct anatomical and behavioral phenotypes. In Tg mice, MBP-reactive T-cells are activated by spinal cord injury (SCI), causing more severe axonal injury, demyelination, and functional impairment than is found in non-Tg wild-type mice (B10.PL). Conversely, despite a robust SCI-induced T-cell response in B10.PL mice, no overt T-cell-mediated pathology was evident. Here, we show that chronic intraspinal T-cell accumulation in B10.PL and Tg mice is associated with a dramatic and sustained increase in CXCL10/IP-10 and CCL5/RANTES mRNA expression. However, in Tg mice, chemokine mRNA were enhanced 2- to 17-fold higher than in B10.PL mice and were associated with accelerated intraspinal T-cell influx and enhanced CNS macrophage activation throughout the spinal cord. These data suggest common molecular pathways for initiating T-cell responses after SCI in mice; however, if T-cell reactions are biased against MBP, molecular and cellular determinants of neuroinflammation are magnified in parallel with exacerbation of neuropathology and functional impairment.

Lymphocytes and autoimmunity after spinal cord injury.

Over the past 15 years an immense amount of data has accumulated regarding the infiltration and activation of lymphocytes in the traumatized spinal cord. Although the impact of the intraspinal accumulation of lymphocytes is still unclear, modulation of the adaptive immune response via active and passive vaccination is being evaluated for its preclinical efficacy in improving the outcome for spinal-injured individuals. The complexity of the interaction between the nervous and the immune systems is highlighted in the contradictions that appear in response to these modulations. Current evidence regarding augmentation and inhibition of the adaptive immune response to spinal cord injury is reviewed with an aim toward reconciling conflicting data and providing consensus issues that may be exploited in future therapies. Opportunities such an approach may provide are highlighted as well as the obstacles that must be overcome before such approaches can be translated into clinical trials.

Cellular Neuroinflammation in a Lateral Forceps Compression Model of Spinal Cord Injury

Postinjury inflammation has been implicated in secondary degeneration following injury to the spinal cord. The cellular inflammatory response to injury has not been described in the lateral compression injury model, although various types of compression injuries account for ∼20% of human spinal cord injuries (SCI). Here, we used forceps to induce a moderate compression injury to the thoracic spinal cord of female Sprague‐Dawley rats. We evaluated innate and adaptive components of the inflammatory response at various times postinjury using immunohistochemical techniques. We show that components of innate immunity (e.g., macrophages and dendritic cells) peak between 1 and 2 weeks postinjury but persist through 42 days postinjury (dpi). CD163 and CD206 expression, associated with an anti‐inflammatory, reparative phenotype, was upregulated on activated macrophages in the injury site, as were MHC class II antigens. The expression of MHC class II antigens is necessary for the initiation of adaptive immunity and was accompanied by an influx of T cells. T cells were initially restricted to gray matter at the injury epicenter but were later observed throughout the lesioned parenchyma. In summary, we demonstrate that lateral forceps compression of the spinal cord produces a neuroinflammatory response similar to that described in human spinal cord trauma and in other experimental models of spinal cord trauma, thus is an appropriate model to study secondary neurodegeneration in SCI. Anat Rec, 2013.

The Immune System of the Brain

Abstract Historically, the central nervous system (CNS) was believed to be anatomically and physiologically isolated from the immune system. The existence of a book entitled “ Neuroimmune Biology ” is evidence that this concept of CNS “immune privilege” has evolved and neuroimmunology has emerged at the cutting edge of experimental and clinical neuroscience. Today, we know that cells and mediators of the immune system routinely access the intact brain and spinal cord. Furthermore, neurons and glia interact with and regulate inflammatory leukocytes under normal and pathological conditions. This chapter provides an overview of the historical concept of immune privilege and presents evidence that mandates a reappraisal of this dogma. Specifically, new data suggest that the CNS and the immune system actively regulate each other through discrete cellular and molecular mechanisms and when this control is disrupted, pathology ensues.

IDENTIFICATION OF A WIDE VARIETY OF BACTERIA IN THE BRAIN TISSUE OF INDIVIDUALS WITH EITHER MILD COGNITIVE IMPAIRMENT (MCI) OR ALZHEIMER’S DISEASE

results were compared to those of 20 healthy sex and age matched healthy controls(HC). Mechanisms regulating inflammasome signaling involves the priming signal to upregulate the expression of NLRP3 and signal 2 to activate the functional NLRP3; thus monocytes were either primed with LPS(1mg/ml for 2h) and stimulated with Aß42 AlexaFluor488 (FAM)-labeled (10mg/ml) for 24h or stimulated with Aß42 FAM alone for 24h in the presence/absence of Stavudine (50mM) for 22h. Aß-phagocytosis was analyzed by Imagines–FlowCitometry; caspase1 and cytokines were quantified by ELISA. Results: Results showed that: 1) Caspase1, IL1ß and IL18 production by LPS and Aß42 stimulated monocytes of AD patients was significantly increased compared to HC (for all p<0.05); 2) Aß-phagocytosis was significantly reduced in LPS-primed and Aß42 stimulated cells of AD and HC individuals compared to those stimulated with Aß42 alone (for both p<0.05); 3) Stavudine resulted in a drastic reduction of Caspase1, IL1ß and IL18 production (p<0.05) but did not modify the Aß-phagocytosis capacity of monocytes. Conclusions:NLRP3 inflammasome-driven inflammation reduces monocytes mediated Aß phagocytosis in AD and HC. Stavudine dampens NLRP3 activation and downstream inflammation but does not significantly modify Aß-phagocytosis. These results suggest that, even if Stavudine could be useful in modulating neuroinflammation in AD, AD-associated impairments in Aßphagocytosis are not a consequence of a direct consequence of inflammation.

#93 Alterations in sympathetic nervous system and hypothalamic–pituitary–adrenal axis function after experimental spinal cord injury

Maintenance of normal immune function (e.g., cytokine release, antibody synthesis) may be impaired after spinal cord injury (SCI) due to sympathetic nervous system (SNS) and hypothalamic–pituitary–adrenal (HPA) axis dysfunction. Indeed, systemic norepinephrine (NE) and cortisol can be elevated chronically after SCI leaving patients susceptible to infection. To model these changes in rodents, we have used both midand high-thoracic spinal contusion and transection injuries in rats and mice. Following spinal contusion (T8/9) in rats, serum corticosterone (CORT) is elevated up to 28 days post-injury (dpi). In SCI mice, an identical lesion produces similar acute elevations of CORT (1–3 dpi) but with a return toward baseline by 7 dpi. However, circadian cycling of CORT release remains disrupted up to 28 dpi. Similarly, because the SNS innervates the spleen and because SCI damages SNS preganglionic neurons at the level of injury and in nearby spinal segments, we predicted SCI would induce an abrupt spike in splenic NE. However, after T9 spinal contusion or transection injury in mice, splenic NE levels were unchanged. Conversely, when supraspinal input was removed at higher spinal levels (e.g., T3 transection), splenic NE was markedly increased. Associated with this NE spike was an upregulation of splenocyte b2-adrenergic receptor mRNA expression. Together, these data indicate that the SNS and HPA axis are disrupted after SCI, with the dysregulation being more prominent after higher level injuries. Additional studies are needed to determine how these changes influence the initiation, progression, and resolution of immunological function.