Spinal cord injuries disrupt central autonomic pathways that regulate immune function, and increasing evidence suggests that this may cause deficiencies in immune responses in people with spinal cord injuries. Here we analyze the consequences of spinal cord injury (SCI) on immune responses following experimental viral infection of mice. Female C57BL/6 mice received complete crush injuries at either thoracic level 3 (T3) or 9 (T9), and 1 week post-injury, injured mice and un-injured controls were infected with different dosages of mouse hepatitis virus (MHV, a positive-strand RNA virus). Following MHV infection, T3- and T9-injured mice exhibited increased mortality in comparison to un-injured and laminectomy controls. Infection at all dosages resulted in significantly higher viral titer in both T3- and T9-injured mice compared to un-injured controls. Investigation of anti-viral immune responses revealed impairment of cellular infiltration and effector functions in mice with SCI. Specifically, cell-mediated responses were diminished in T3-injured mice, as seen by reduction in virus-specific CD4+ T lymphocyte proliferation and IFN-γ production and decreased numbers of activated antigen presenting cells compared to infected un-injured mice. Collectively, these data indicate that the inability to control viral replication following SCI is not level dependent and that increased susceptibility to infection is due to suppression of both innate and adaptive immune responses.
A fundamental component of signaling initiated by the BCR and CD19 is the activation of phosphoinositide 3-kinase. Downstream of phosphoinositide 3-kinase, the protein kinase AKT phosphorylates several substrates, including members of the forkhead box subgroup O (Foxo) transcription factor family. Among the Foxo proteins, Foxo1 has unique functions in bone marrow B-cell development and peripheral B-cell function. Here, we report a previously unrecognized role for Foxo1 in controlling the ratio of mature B-cell subsets in the spleen. Conditional deletion of Foxo1 in B cells resulted in an increased percentage of marginal zone B cells and a decrease in follicular (FO) B cells. In addition, Foxo1 deficiency corrected the absence of marginal zone B cells that occurs in CD19-deficient mice. These findings show that Foxo1 regulates the balance of mature B-cell subsets and is required for the marginal zone B-cell deficiency phenotype of mice lacking CD19. IntroductionBCR crosslinking activates phosphoinositide 3-kinase (PI3K), the lipid products of which orchestrate the assembly of membraneassociated signaling complexes [1]. One group of proteins, termed the BCR signalosome, is responsible for maximal activation of phospholipase Cg and subsequent phosphoinositide hydrolysis and Ca 21 mobilization. Another outcome of PI3K signaling is the activation of AKT. The AKT serine/threonine kinases have numerous substrates, whose phosphorylation state controls diverse processes including proliferation, survival, metabolism and differentiation. The roles of most AKT substrates in B-cell biology have not been defined.CD19 is a transmembrane protein that enhances BCR signaling by multiple mechanisms [2,3]. CD19 interacts with CD21 and CD81 to form the B-cell co-receptor, which clusters with the BCR in response to complement-tagged antigens to augment signaling. CD19 can also associate with the BCR in the absence of CD21 to promote BCR signalosome assembly upon recognition of membrane-associated antigens [4]. The cytoplasmic tail of CD19 contains two canonical motifs for recruitment of PI3K (YXXM), and these are required for CD19 function [5]. Genetic evidence supports a functional role for AKT downstream of CD19, in that combined deletion of two AKT genes (Akt1 and Akt2) in mouse B cells confers a defect in marginal zone (MZ) B-cell development [6] similar to the phenotype of CD19-deficient mice [5,7]. However, it is not yet clear which AKT substrates regulate MZ-cell development.Forkhead box subgroup O (Foxo) transcription factors activate or suppress target genes in a cell type-specific and contextdependent manner [8,9]. In resting lymphocytes, Foxo proteins are localized to the nucleus and activate genes that maintain quiescence as well as proper homing and recirculation [1]. Phosphorylation by AKT causes cytoplasmic sequestration and SHORT COMMUNICATION Results and discussion Deletion of Foxo1 affects B-cell developmentWe generated a conditional Foxo1 allele by inserting LoxP sites flanking the first exon of Foxo1 [11]. Mice ...
The oral drug FTY720 affects sphingosine-1-phosphate (S1P) signaling on targeted cells that bear the S1P receptors S1P1, S1P3, S1P4, and S1P5. We examined the effect of FTY720 treatment on the biology of mouse neural progenitor cells (NPCs) after transplantation in a viral model of demyelination. Intracerebral infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV) resulted in an acute encephalomyelitis, followed by demyelination similar in pathology to the human demyelinating disease, multiple sclerosis. We have previously reported that intraspinal transplantation of mouse NPCs into JHMV-infected animals resulted in selective colonization of demyelinated lesions, preferential differentiation into oligodendroglia accompanied by axonal preservation, and increased remyelination. Cultured NPCs expressed transcripts for S1P receptors S1P1, S1P2, S1P3, S1P4, and S1P5. FTY720 treatment of cultured NPCs resulted in increased mitogen-activated protein kinase phosphorylation and migration after exposure to the chemokine CXCL12. Administration of FTY720 to JHMV-infected mice resulted in enhanced migration and increased proliferation of transplanted NPCs after spinal cord engraftment. FTY720 treatment did not improve clinical disease, diminish neuroinflammation or the severity of demyelination, nor increase remyelination. These findings argue that FTY720 treatment selectively increases NPC proliferation and migration but does not either improve clinical outcome or enhance remyelination after transplantation into animals in which immune-mediated demyelination is initiated by the viral infection of the central nervous system. Intracranial infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in an acute encephalomyelitis, followed by chronic demyelination characterized by viral persistence within the central nervous system (CNS), axonal damage, and demyelination.1e7 Previous studies from our laboratory have used the JHMV model of neuroinflammation-mediated demyelination to evaluate the therapeutic benefit of mouse neural progenitor cell (NPC) engraftment on remyelination.8e10 Transplantation of mouse NPCs into the spinal cords of JHMV-infected mice results in extensive migration and colonization of areas of white matter damage and preferential differentiation into oligodendroglia.8e10 Engrafted NPCs physically engage damaged axons, and this ultimately leads to increased axonal integrity that correlates with remyelination. 8,11 These findings, along with others,
BackgroundFTY720 (fingolimod) is the first oral drug approved by the Food and Drug Administration for treatment of patients with the relapsing-remitting form of the human demyelinating disease multiple sclerosis. Evidence suggests that the therapeutic benefit of FTY720 occurs by preventing the egress of lymphocytes from lymph nodes thereby inhibiting the infiltration of disease-causing lymphocytes into the central nervous system (CNS). We hypothesized that FTY720 treatment would affect lymphocyte migration to the CNS and influence disease severity in a mouse model of viral-induced neurologic disease.MethodsMice were infected intracranially with the neurotropic JHM strain of mouse hepatitis virus. Infected animals were treated with increasing doses (1, 3 and 10 mg/kg) of FTY720 and morbidity and mortality recorded. Infiltration of inflammatory virus-specific T cells (tetramer staining) into the CNS of FTY720-treated mice was determined using flow cytometry. The effects of FTY720 treatment on virus-specific T cell proliferation, cytokine production and cytolytic activity were also determined. The severity of neuroinflammation and demyelination in FTY720-treated mice was examined by flow cytometry and histopathologically, respectively, in the spinal cords of the mice.ResultsAdministration of FTY720 to JHMV-infected mice resulted in increased clinical disease severity and mortality. These results correlated with impaired ability to control viral replication (P < 0.05) within the CNS at days 7 and 14 post-infection, which was associated with diminished accumulation of virus-specific CD4+ and CD8+ T cells (P < 0.05) into the CNS. Reduced neuroinflammation in FTY720-treated mice correlated with increased retention of T lymphocytes within draining cervical lymph nodes (P < 0.05). Treatment with FTY720 did not affect virus-specific T cell proliferation, expression of IFN-γ, TNF-α or cytolytic activity. FTY720-treated mice exhibited a reduction in the severity of demyelination associated with dampened neuroinflammation.ConclusionThese findings indicate that FTY720 mutes effective anti-viral immune responses through impacting migration and accumulation of virus-specific T cells within the CNS during acute viral-induced encephalomyelitis. FTY720 treatment reduces the severity of neuroinflammatory-mediated demyelination by restricting the access of disease-causing lymphocytes into the CNS but is not associated with viral recrudescence in this model.
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