Human microglia and astrocytes constitutively express the neurokinin-1 receptor and functionally respond to substance P.

BACKGROUND: The tachykinin substance P (SP) is recognized to exacerbate inflammation at peripheral sites via its target receptor, neurokinin 1 receptor (NK-1R), expressed by leukocytes. More recently, SP/NK-1R interactions have been associated with severe neuroinflammation and neuronal damage. We have previously demonstrated that NK-1R antagonists can limit neuroinflammatory damage in a mouse model of bacterial meningitis. Furthermore, we have since shown that these agents can attenuate bacteria-induced neuronal and glial inflammatory mediator production in nonhuman primate (NHP) brain explants and isolated neuronal cells, and following in vivo infection. METHODS: In the present study, we have assessed the ability of NHP brain explants, primary human microglia and astrocytes, and immortalized human glial cell lines to express NK-1R isoforms. We have utilized RT-PCR, immunoblot analysis, immunofluorescent microscopy, and/or flow cytometric analysis, to quantify NK-1R expression in each, at rest, or following bacterial challenge. Furthermore, we have assessed the ability of human microglia to respond to SP by immunoblot analysis of NF-kB nuclear translocation and determined the ability of this neuropeptide to augment inflammatory cytokine release and neurotoxic mediator production by human astrocytes using an ELISA and a neuronal cell toxicity assay, respectively. RESULTS: We demonstrate that human microglial and astrocytic cells as well as NHP brain tissue constitutively express robust levels of the full-length NK-1R isoform. In addition, we demonstrate that the expression of NK-1R by human astrocytes can be further elevated following exposure to disparate bacterial pathogens or their components. Importantly, we have demonstrated that NK-1R is functional in both human microglia and astrocytes and show that SP can augment the inflammatory and/or neurotoxic immune responses of glial cells to disparate and clinically relevant bacterial pathogens. CONCLUSIONS: The robust constitutive and functional expression of the full-length NK-1R isoform by human microglia and astrocytes, and the ability of SP to augment inflammatory signaling pathways and mediator production by these cells, support the contention that SP/NK-1R interactions play a significant role in the damaging neuroinflammation associated with conditions such as bacterial meningitis.

Triple-acting Lytic Enzyme Treatment of Drug-Resistant and Intracellular Staphylococcus aureus.

Multi-drug resistant bacteria are a persistent problem in modern health care, food safety and animal health. There is a need for new antimicrobials to replace over used conventional antibiotics. Here we describe engineered triple-acting staphylolytic peptidoglycan hydrolases wherein three unique antimicrobial activities from two parental proteins are combined into a single fusion protein. This effectively reduces the incidence of resistant strain development. The fusion protein reduced colonization by Staphylococcus aureus in a rat nasal colonization model, surpassing the efficacy of either parental protein. Modification of a triple-acting lytic construct with a protein transduction domain significantly enhanced both biofilm eradication and the ability to kill intracellular S. aureus as demonstrated in cultured mammary epithelial cells and in a mouse model of staphylococcal mastitis. Interestingly, the protein transduction domain was not necessary for reducing the intracellular pathogens in cultured osteoblasts or in two mouse models of osteomyelitis, highlighting the vagaries of exactly how protein transduction domains facilitate protein uptake. Bacterial cell wall degrading enzyme antimicrobials can be engineered to enhance their value as potent therapeutics.

Astrocytes produce IL-19 in response to bacterial challenge and are sensitive to the immunosuppressive effects of this IL-10 family member.

There is growing appreciation that resident glial cells can initiate and/or regulate inflammation following trauma or infection in the central nervous system (CNS). We have previously demonstrated the ability of microglia and astrocytes to respond to bacterial pathogens or their products by rapid production of inflammatory mediators, followed by the production of the immunosuppressive cytokine interleukin (IL)−10. IL-19, another member of the IL-10 family of cytokines, has been studied in the context of a number of inflammatory conditions in the periphery and is known to modulate immune cell activity. In the present study, we demonstrate the constitutive and/or inducible expression of IL-19 and its cognate receptor subunits, IL-19Rα and IL-19Rß (also known as IL-20R1 and IL-20R2, and IL-20RA and IL-20RB), in mouse brain tissue, and by primary murine and human astrocytes. We also provide evidence for the presence of a novel truncated IL-19Rα transcript variant in mouse brain tissue, but not glial cells, that shows reduced expression following bacterial infection. Importantly, IL-19R functionality in glia is indicated by the ability of IL-19 to regulate signaling component expression in these cells. Furthermore, while IL-19 itself had no effect on glial cytokine production, IL-19 treatment of bacterially infected or Toll-like receptor ligand stimulated astrocytes significantly attenuated pro-inflammatory cytokine production. The bacterially induced production of IL-19 by these resident CNS cells, the constitutive expression of its cognate receptor subunits, and the immunomodulatory effects of this cytokine, suggest a novel mechanism by which astrocytes can regulate CNS inflammation.

Alpha beta-crystallin expression and presentation following infection with murine gammaherpesvirus 68.

Alpha beta-crystallin (CRYAB) is a small heat shock protein that can function as a molecular chaperone and has protective effects for cells undergoing a variety of stressors. Surprisingly, CRYAB has been identified as one of the dominant autoantigens in multiple sclerosis. It has been suggested that autoimmune mediated destruction of this small heat shock protein may limit its protective effects, thereby exacerbating inflammation and cellular damage during multiple sclerosis. It is not altogether clear how autoimmunity against CRYAB might develop, or whether there are environmental factors which might facilitate the presentation of this autoantigen to CD4+ T lymphocytes. In the present study, we utilized an animal model of an Epstein Barr Virus (EBV)-like infection, murine gammaherpesvirus 68 (HV-68), to question whether such a virus could modulate the expression of CRYAB by antigen presenting cells. Following exposure to HV-68 and several other stimuli, in vitro secretion of CRYAB and subsequent intracellular accumulation were observed in cultured macrophages and dendritic cells. Following infection of mice with this virus, it was possible to track CRYAB expression in the spleen and in antigen presenting cell subpopulations, as well as its secretion into the blood. Mice immunized with human CRYAB mounted a significant immune response against this heat shock protein. Further, dendritic cells that were exposed to HV-68 could stimulate CD4+ T cells from CRYAB immunized mice to secrete interferon gamma. Taken together these studies are consistent with the notion of a gammaherpesvirus-induced CRYAB response in professional antigen presenting cells in this mouse model.

An expanded myeloid derived suppressor cell population does not play a role in gammaherpesvirus-exacerbated breast cancer metastases.

BACKGROUND: Mice latently infected with murine gammaherpesvirus 68 (HV-68) and transplanted with 4 T1 breast cancer cells developed exacerbated metastatic lesions when compared to controls. The mechanisms responsible for this viral-exacerbated disease were not clear. The ability of HV-68 infection to induce S100A8 and S100A9 production and to expand a population of CD11b+Gr-1+ cells suggested that increased numbers, or activity, of viral-expanded myeloid derived suppressor cells (MDSCs) might contribute to HV-68-associated metastatic breast cancer in this model. We questioned whether mock or HV-68 infected mice with significant breast cancer might have differences in the number and/or activity of MDSCs. METHODS: Myeloid-derived macrophages and dendritic cells were isolated from normal mice and cultured in vitro with HV-68 to assess S100A8 and S100A9 mRNA and protein expression. In vivo studies were performed using groups of mice that were mock treated or infected with HV-68. After viral latency was established, 4 T1 breast cancer cells were transplanted in mice. When primary breast tumors were present mice were euthanized and cells isolated for phenotyping of myeloid cell populations using FACS, and for ex vivo analysis of suppressor activity. Serum from these animals was also collected to quantify S100A8 and S100A9 levels. RESULTS: In vitro studies demonstrated that direct exposure of myeloid cells to HV-68 did not induce increased expression of S100A8 or S100A9 mRNAs or secreted protein. HV-68 infected mice with metastatic breast cancer disease had no increases in S100A8/A9 levels and no significant increases in the numbers or activation of CD11b+Gr-1+MDSCs when compared to mock treated mice with breast cancer. CONCLUSIONS: Together these studies are consistent with the notion that expanded myeloid derived suppressor cells do not play a role in gammaherpesvirus-exacerbated breast cancer metastases. The mechanisms responsible for HV-68 induced exacerbation of metastatic breast cancer remain unclear.

Exacerbated metastatic disease in a mouse mammary tumor model following latent gammaherpesvirus infection.

BACKGROUND: Controversy exists as to the ability of human gammaherpesviruses to cause or exacerbate breast cancer disease in patients. The difficulty in conducting definitive human studies can be overcome by investigating developing breast cancer in a mouse model. In this study, we utilized mice latently infected with murine gammaherpesvirus 68 (HV-68) to question whether such a viral burden could exacerbate metastatic breast cancer disease using a mouse mammary tumor model. RESULTS: Mice latently infected with HV-68 had a similar primary tumor burden, but much greater metastatic disease, when compared to mock treated mice given the transplantable tumor, 4 T1. This was true for lung lesions, as well as secondary tumor masses. Increased expression of pan-cytokeratin and VEGF-A in tumors from HV-68 infected mice was consistent with increased metastatic disease in these animals. Surprisingly, no viral particles could be cultured from tumor tissues, and the presence of viral DNA or RNA transcripts could not be detected in primary or secondary tumor tissues. CONCLUSIONS: Latent HV-68 infection had no significant effect on the size of primary 4 T1 mammary tumors, but exacerbated the number of metastatic lung lesions and secondary tumors when compared to mock treated mice. Increased expression of the tumor marker, pan-cytokeratin, and VEGF-A in tumors of mice harboring latent virus was consistent with an exacerbated metastatic disease. Mechanisms responsible for this exacerbation are indirect, since no virus could be detected in cancerous tissues.

Murine gammaherpesvirus-68 expands, but does not activate, CD11b+ gr-1+ splenocytes in vivo.

BACKGROUND: Murine gammaherpesvirus 68 (HV-68) is an efficient pathogen, capable of infecting and establishing lifelong latency in rodents. While many studies have demonstrated the ability of this viral infection to modulate immune responses, a unifying mechanism for HV-68-induced subversion of a protective host response remains elusive. We questioned whether infection with HV-68 could expand a population of myeloid derived suppressor cells (MDSC) as one mechanism for altering protective immunity. METHODS: Mice were infected with HV-68, with viral latency being established in these animals. At varying times post-infection, cells were isolated for detection of viral genomes, phenotyping of myeloid cell populations, and ex vivo analysis of suppressor activity of myeloid cells. RESULTS: CD11b + Gr-1+ myeloid cells accumulated in the spleens, but not the bone marrow, of HV-68 infected mice. These cells were predominantly Gr-1+ Ly-6 G+, and could be found to contain viral genomes. Increased levels of serum S100A8/A9 produced during viral infection were consistent with the expansion of these CD11b + Gr-1+ myeloid cells. Despite their expansion, these cells exhibited no increased arginase 1 or iNOS activity, and did not have the ability to suppress anti-CD3 antibody activated T lymphocyte responses. CONCLUSIONS: We concluded that HV-68 infection was capable of expanding a population of myeloid cells which were phenotypically similar to MDSC. However these cells were not sufficiently activated during the establishment of viral latency to actively suppress T cell responses.

A role for DNA-dependent activator of interferon regulatory factor in the recognition of herpes simplex virus type 1 by glial cells.

BACKGROUND: The rapid onset of potentially lethal neuroinflammation is a defining feature of viral encephalitis. Microglia and astrocytes are likely to play a significant role in viral encephalitis pathophysiology as they are ideally positioned to respond to invading central nervous system (CNS) pathogens by producing key inflammatory mediators. Recently, DNA-dependent activator of IFN regulatory factor (DAI) has been reported to function as an intracellular sensor for DNA viruses. To date, the expression and functional role of DAI in the inflammatory responses of resident CNS cells to neurotropic DNA viruses has not been reported. METHODS: Expression of DAI and its downstream effector molecules was determined in C57BL/6-derived microglia and astrocytes, either at rest or following exposure to herpes simplex virus type 1 (HSV-1) and/or murine gammaherpesvirus-68 (MHV-68), by immunoblot analysis. In addition, such expression was studied in ex vivo microglia/macrophages and astrocytes from uninfected animals or mice infected with HSV-1. Inflammatory cytokine production by glial cultures following transfection with a DAI specific ligand (B-DNA), or following HSV-1 challenge in the absence or presence of siRNA directed against DAI, was assessed by specific capture ELISA. The production of soluble neurotoxic mediators by HSV-1 infected glia following DAI knockdown was assessed by analysis of the susceptibility of neuron-like cells to conditioned glial media. RESULTS: We show that isolated microglia and astrocytes constitutively express DAI and its effector molecules, and show that such expression is upregulated following DNA virus challenge. We demonstrate that these resident CNS cells express DAI in situ, and show that its expression is similarly elevated in a murine model of HSV-1 encephalitis. Importantly, we show B-DNA transfection can elicit inflammatory cytokine production by isolated glial cells and DAI knockdown can significantly reduce microglial and astrocyte responses to HSV-1. Finally, we demonstrate that HSV-1 challenged microglia and astrocytes release neurotoxic mediators and show that such production is significantly attenuated following DAI knockdown. CONCLUSIONS: The functional expression of DAI by microglia and astrocytes may represent an important innate immune mechanism underlying the rapid and potentially lethal inflammation associated with neurotropic DNA virus infection.

Prophylactic and therapeutic targeting of the neurokinin-1 receptor limits neuroinflammation in a murine model of pneumococcal meningitis.

There is increasing evidence that the tachykinin substance P (SP) can augment inflammatory immune responses within the CNS. We have recently demonstrated that resident CNS cells express high-affinity receptors for this neuropeptide (neurokinin-1 receptors [NK-1R]), and we have shown that SP can significantly augment glial inflammatory responses to clinically relevant Gram-negative bacteria. Furthermore, we provided evidence that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation following in vivo exposure to these pathogens. In this study, we demonstrate that SP similarly enhances inflammatory glial responses to the major Gram-positive causative agent of bacterial meningitis, Streptococcus pneumoniae, and show that endogenous SP/NK-1R interactions play a critical role in the development of CNS inflammation in an in vivo model of pneumococcal meningitis. Importantly, we provide the first demonstration, to our knowledge, that pharmacological targeting of the NK-1R not only prevents the development of damaging inflammation when administered prophylactically, but can also limit or reverse neuroinflammation associated with an established streptococcal CNS infection when delivered therapeutically. We show that an NK-1R antagonist attenuates increases in CNS inflammatory cytokine levels and decreases in immunosuppressive cytokine production associated with an ongoing S. pneumoniae infection. Furthermore, we demonstrate that such a therapeutic intervention reverses infection-associated gliosis and demyelination in the absence of changes in CNS bacterial burden. Together, these results suggest that targeting SP/NK-1R interactions is a strategy worthy of further study for the treatment of microbially induced neuroinflammation.

Causative agents of osteomyelitis induce death domain-containing TNF-related apoptosis-inducing ligand receptor expression on osteoblasts.

Bacteria and their products are potent inducers of bone destruction. While inflammatory damage during conditions such as osteomyelitis is associated with increased formation and activity of bone-resorbing osteoclasts, it is likely that bone loss also results from the elimination of the cells responsible for matrix deposition. Consistent with this notion, we have previously demonstrated that bone-forming osteoblasts undergo apoptosis following bacterial challenge and that this cell death is due, at least in part, to the actions of TNF-related apoptosis-inducing ligand (TRAIL). In the present study, we demonstrate that primary osteoblasts constitutively express death domain containing TRAIL receptors. Importantly, we show that cell surface expression of the death-inducing receptors DR4 and DR5 on murine and human osteoblasts is restricted to cells infected with the principle causative agents of osteomyelitis, Staphylococcus aureus and Salmonella. In addition, we show that the robust constitutive production by osteoblasts of the decoy TRAIL receptor, OPG, is inhibited following bacterial infection. Finally, we report that while exogenous administration of TRAIL fails to activate apoptosis signaling pathways in uninfected osteoblasts, acute bacterial exposure sensitizes these cells to this ligand. Based upon these findings we suggest a model in which bacterially challenged osteoblasts express TRAIL while concomitantly decreasing the production of the decoy receptor OPG and upregulating cell surface death receptor expression. Such an increase in TRAIL bioavailability and induced sensitivity of infected osteoblasts to this ligand would result in apoptotic cell death of this bone-forming population, providing an additional mechanism underlying inflammatory bone loss during diseases such as osteomyelitis.

Differential roles for NOD2 in osteoblast inflammatory immune responses to bacterial pathogens of bone tissue.

Osteoblasts produce an array of immune molecules following bacterial challenge that can contribute to inflammation and the recruitment of leukocytes to sites of infection during bone diseases such as osteomyelitis. However, the mechanisms by which osteoblasts perceive and respond to facultative intracellular pathogens such as Salmonella species and Staphylococcus aureus have not been determined. Recently, our laboratory has described the expression in osteoblasts of members of the nucleotide-binding domain leucine-rich repeat region containing family of proteins that include nucleotide-binding oligomerization domain-2 (NOD2), a molecule that functions as an intracellular receptor for bacterial peptidoglycans. In the present study, we demonstrate that NOD2 expression is required for select inflammatory mediator production by osteoblasts following infection with the invasive pathogen Salmonella. In contrast, we have found that the inflammatory immune responses of osteoblasts to the passively internalized bacterial species Staphylococcus aureus, heat-killed pathogenic Salmonella, a non-invasive Salmonella strain and specific Toll-like receptor ligands are not reduced in the absence of NOD2 expression but are, in fact, elevated. Based upon these findings, we suggest that NOD2 serves differential roles in osteoblasts, promoting inflammatory responses to invasive bacteria while tempering cell responses to extracellular and/or passively internalized bacterial species.

NOD2 contributes to the inflammatory responses of primary murine microglia and astrocytes to Staphylococcus aureus.

We have recently demonstrated that microglia and astrocytes express nucleotide-binding oligomerization domain-2 (NOD2), a novel cytosolic pattern recognition receptor for bacterial motifs, and we have shown that this intracellular receptor is essential for glial responses to Gram-negative pathogens. Here, we demonstrate that intact Staphylococcus aureus, a major Gram-positive causative agent of brain abscesses, activates the transcription factor NF-kappaB and is a potent stimulus for inflammatory cytokine production in primary murine microglia and astrocytes. Interestingly, we demonstrate that NOD2 is essential for maximal glial responses to intact S. aureus, but not cellular lysates. As such, this data indicates that NOD2 plays an important role in initiating inflammatory mediator production by resident brain cells following S. aureus infection and we suggest that this cytosolic receptor acts in conjunction with cell surface pattern recognition receptors to elicit maximal glial responses.

Vesicular stomatitis virus infects resident cells of the central nervous system and induces replication-dependent inflammatory responses.

Vesicular stomatitis virus (VSV) infection of mice via intranasal administration results in a severe encephalitis with rapid activation and proliferation of microglia and astrocytes. We have recently shown that these glial cells express RIG-I and MDA5, cytosolic pattern recognition receptors for viral RNA. However, it is unclear whether VSV can replicate in glial cells or if such replication is required for their inflammatory responses. Here we demonstrate that primary microglia and astrocytes are permissive for VSV infection and limited productive replication. Importantly, we show that viral replication is required for robust inflammatory mediator production by these cells. Finally, we have confirmed that in vivo VSV administration can result in viral infection of glial cells in situ. These results suggest that viral replication within resident glial cells might play an important role in CNS inflammation following infection with VSV and possibly other neurotropic nonsegmented negative-strand RNA viruses.

NOD2 mediates inflammatory responses of primary murine glia to Streptococcus pneumoniae.

It is now widely accepted that resident central nervous system (CNS) cells such as microglia and astrocytes initiate and/or augment inflammation following trauma or infection. However, the mechanisms by which glial cells perceive microbial challenges are only now becoming apparent. We have recently demonstrated that microglia and astrocytes constitutively express nucleotide-binding oligomerization domain-2 (NOD2), a member of the novel nucleotide-binding domain leucine-rich repeat region-containing family of proteins (NLR) that functions as an intracellular receptor for a minimal motif present in all bacterial peptidoglycans. Furthermore, we have shown that this NLR is essential for glial responses to gram-negative pathogens and in vivo CNS inflammation elicited by these organisms. In the present study, we have established that intact Streptococcus pneumoniae, the major causative agent for gram-positive bacterial meningitis in adults, is a potent stimulus for the activation of the pivotal inflammatory transcription factor NF-kB and production of inflammatory cytokines in primary murine microglia and astrocytes. We demonstrate that NOD2 is essential for the maximal responses of these cells to intact S. pneumoniae but not cellular lysates. Finally, we have shown that this cytosolic pattern recognition receptor is required for the elevated inflammatory mediator levels, astrogliosis, and demyelination, following in vivo administration of this gram-positive CNS pathogen. As such, we suggest that NOD2 plays a critical role in the establishment of the lethal inflammation associated with streptococcal meningitis.

NOD2 plays an important role in the inflammatory responses of microglia and astrocytes to bacterial CNS pathogens.

While glial cells are recognized for their roles in maintaining neuronal function, there is growing appreciation that resident central nervous system (CNS) cells initiate and/or augment inflammation following trauma or infection. We have recently demonstrated that microglia and astrocytes constitutively express nucleotide-binding oligomerization domain-2 (NOD2), a member of the novel nucleotide-binding domain leucine-rich repeat region containing a family of proteins (NLR) that functions as an intracellular receptor for a minimal motif present in all bacterial peptidoglycans. In this study, we have confirmed the functional nature of NOD2 expression in astrocytes and microglia and begun to determine the relative contribution that this NLR makes in inflammatory CNS responses to clinically relevant bacterial pathogens. We demonstrate the increased association of NOD2 with its downstream effector molecule, Rip2 kinase, in primary cultures of murine microglia and astrocytes following exposure to bacterial antigens. We show that this cytosolic receptor underlies the ability of muramyl dipeptide to augment the production of inflammatory cytokines by glia following exposure to specific ligands for disparate Toll-like receptor homologues. In addition, we demonstrate that NOD2 is an important component in the in vitro inflammatory responses of resident glia to N. meningitidis and B. burgdorferi antigens. Finally, we have established that NOD2 is required, at least in part, for the astrogliosis, demyelination, behavioral changes, and elevated inflammatory cytokine levels observed following in vivo infection with these pathogens. As such, we have identified NOD2 as an important component in the generation of damaging CNS inflammation following bacterial infection.

Characterization of retinoic acid-inducible gene-I expression in primary murine glia following exposure to vesicular stomatitis virus.

Vesicular stomatitis virus (VSV) is a negative-sense single-stranded RNA virus that closely resembles its deadly cousin, rabies virus. In mice, VSV elicits a rapid and severe T cell-independent encephalitis, indicating that resident glial cells play an important role in the initiation of central nervous system (CNS) inflammation. Recently, retinoic acid-inducible gene I (RIG-I)-like helicases have been shown to function as intracellular pattern recognition receptors for replicative viral RNA motifs. In the present study, we demonstrate that the expression of two members of this RIG-I-like receptor family (RLR), RIG-I and melanoma differentiation-associated antigen 5 (MDA5), are elevated in mouse brain tissue following intranasal administration of VSV. Using isolated cultures of primary murine glial cells, we demonstrate that microglia and astrocytes constitutively express both RIG-I and MDA5 transcripts and protein. Importantly, we show that such expression is elevated following challenge with VSV or another negative-sense RNA virus, Sendai virus. The authors provide evidence that such induction is indirect and secondary to the production of soluble mediators by infected cells. Circumstantial evidence for the functional nature of RLR expression in glial cells comes from the observation that microglia express the RLR downstream effector molecule, interferon promoter stimulator-1, and demonstrate diminished levels of the negative RLR regulator, laboratory of genetics and physiology 2, following viral challenge. These findings raise the exciting possibility that RLR molecules play important roles in the detection of viral CNS pathogens and the initiation of protective immune responses or, alternatively, the progression of damaging inflammation within the brain.

Neurogenic exacerbation of microglial and astrocyte responses to Neisseria meningitidis and Borrelia burgdorferi.

Although glial cells are recognized for their roles in maintaining neuronal function, there is growing appreciation of the ability of resident CNS cells to initiate and/or augment inflammation following trauma or infection. The tachykinin, substance P (SP), is well known to augment inflammatory responses at peripheral sites and its presence throughout the CNS raises the possibility that this neuropeptide might serve a similar function within the brain. In support of this hypothesis, we have recently demonstrated the expression of high affinity receptors for SP (Neurokinin-1 (NK-1) receptors) on microglia and shown that this tachykinin can significantly elevate bacterially induced inflammatory prostanoid production by isolated cultures of these cells. In the present study, we demonstrate that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation in vivo following exposure to two clinically relevant bacterial CNS pathogens, Neisseria meningitidis and Borrelia burgdorferi. We show that in vivo elevations in inflammatory cytokine production and decreases in the production of an immunosuppressive cytokine are markedly attenuated in mice genetically deficient in the expression of the NK-1R or in mice treated with a specific NK-1R antagonist. Furthermore, we have used isolated cultures of microglia and astrocytes to demonstrate that SP can augment inflammatory cytokine production by these resident CNS cell types following exposure to either of these bacterial pathogens. Taken together, these studies indicate a potentially important role for neurogenic exacerbation of resident glial immune responses in CNS inflammatory diseases, such as bacterial meningitis.