CD95-ligand on peripheral myeloid cells activates Syk kinase to trigger their recruitment to the inflammatory site

Activated cytotoxic lymphocytes promote tumor progression by increasing the ability of 3LL tumor cells to mediate MDSC chemoattraction via Fas signaling

The Fas/FasL system transmits intracellular apoptotic signaling, inducing cell apoptosis. However, Fas signaling also exerts non-apoptotic functions in addition to inducing tumor cell apoptosis. For example, Fas signaling induces lung cancer tumor cells to produce prostaglandin E2 (PGE2) and recruit myeloid-derived suppressor cells (MDSCs). Activated cytotoxic T lymphocytes (CTLs) induce and express high levels of FasL, but the effects of Fas activation initiated by FasL in CTLs on apoptosis-resistant tumor cells remain largely unclear. We purified activated CD8(+) T cells from OT-1 mice, evaluated the regulatory effects of Fas activation on tumor cell escape and investigated the relevant mechanisms. We found that CTLs induced tumor cells to secrete PGE2 and increase tumor cell-mediated chemoattraction of MDSCs via Fas signaling, which was favorable to tumor growth. Our results indicate that CTLs may participate in the tumor immune evasion process. To the best of our knowledge, this is a novel mechanism by which CTLs play a role in tumor escape. Our findings implicate a strategy to enhance the antitumor immune response via reduction of negative immune responses to tumors promoted by CTLs through Fas signaling.

The CD95/CD95L signaling pathway: a role in carcinogenesis

Apoptosis is a fundamental process that contributes to tissue homeostasis, immune responses, and development. The receptor CD95, also called Fas, is a member of the tumor necrosis factor receptor (TNF-R) superfamily. Its cognate ligand, CD95L, is implicated in immune homeostasis and immune surveillance, and various lineages of malignant cells exhibit loss-of-function mutations in this pathway; therefore, CD95 was initially classified as a tumor suppressor gene. However, more recent data indicate that in different pathophysiological contexts, this receptor can transmit non-apoptotic signals, promote inflammation, and contribute to carcinogenesis. A comparison with the initial molecular events of the TNF-R signaling pathway leading to non-apoptotic, apoptotic, and necrotic pathways reveals that CD95 is probably using different molecular mechanisms to transmit its non-apoptotic signals (NF-κB, MAPK, and PI3K). As discussed in this review, the molecular process by which the receptor switches from an apoptotic function to an inflammatory role is unknown. More importantly, the biological functions of these signals remain elusive.

Targeting endothelin receptors A and B attenuates the inflammatory response and improves locomotor function following spinal cord injury in mice

After spinal cord injury (SCI), the disruption of blood-spinal cord barrier by activation of the endothelin (ET) system is a critical event leading to leukocyte infiltration, inflammatory response and oxidative stress, contributing to neurological disability. In the present study, we showed that blockade of ET receptor A (ETAR) and/or ET receptor B (ETBR) prevented early inflammatory responses directly via the inhibition of neutrophil and monocyte diapedesis and inflammatory mediator production following traumatic SCI in mice. Long-term neurological improvement, based on a series of tests of locomotor performance, occurred only in the spinal cord‑injured mice following blockade of ETAR and ETBR. We also examined the post‑traumatic changes of the micro-environment within the injured spinal cord of mice following blockade of ET receptors. Oxidative stress reflects an imbalance between malondialdehyde and superoxide dismutase in spinal cord‑injured mice treated with vehicle, whereas blockade of ETAR and ETBR reversed the oxidation state imbalance. In addition, hemeoxygenase-1, a protective protease involved in early SCI, was increased in spinal cord‑injured mice following the blockade of ETAR and ETBR, or only ETBR. Matrix metalloproteinase-9, a tissue-destructive protease involved in early damage, was decreased in the injured spinal cord of mice following blockade of ETAR, ETBR or a combination thereof. The findings of the present study therefore suggested an association between ETAR and ETBR in regulating early pathogenesis of SCI and determining the outcomes of long‑term neurological recovery.

Fas signaling in macrophages promotes chronicity in K/BxN serum-induced arthritis

OBJECTIVE

A nonapoptotic role of Fas signaling has been implicated in the regulation of inflammation and innate immunity. This study was undertaken to elucidate the contribution of Fas signaling in macrophages to the development of arthritis.

METHODS

K/BxN serum-transfer arthritis was induced in a mouse line in which Fas was conditionally deleted in the myeloid lineage (Cre(LysM) Fas(flox/flox) mice). The arthritis was assessed clinically and histologically. Expression of interleukin-1β (IL-1β), CXCL5, IL-10, IL-6, and gp96 was determined by enzyme-linked immunosorbent assay. Bone marrow-derived macrophages were activated with IL-1β and gp96. Cell phenotype and apoptosis were analyzed by flow cytometry.

RESULTS

Arthritis onset in Cre(LysM) Fas(flox/flox) mice was comparable with that observed in control mice; however, resolution was accelerated during the chronic phase. The attenuated arthritis was associated with reduced articular expression of the endogenous Toll-like receptor 2 (TLR-2) ligand gp96 and the neutrophil chemotactic chemokine CXCL5, and enhanced expression of IL-10. Activation with IL-1β or gp96 induced increased IL-10 expression in Fas-deficient murine macrophages compared with control macrophages. IL-10 suppressed IL-6 and CXCL5 expression induced by IL-1β plus gp96. IL-1β-mediated activation of ERK, which regulates IL-10 expression, was increased in Fas-deficient mouse macrophages.

CONCLUSION

Taken together, our findings indicate that impaired Fas signaling results in enhanced expression of antiinflammatory IL-10 and reduced expression of gp96, and these effects are associated with accelerated resolution of inflammation during the chronic phase of arthritis. These observations suggest that strategies to reduce endogenous TLR ligands and increase IL-10 may be beneficial in the treatment of rheumatoid arthritis.

Blockade of Fas signaling in breast cancer cells suppresses tumor growth and metastasis via disruption of Fas signaling-initiated cancer-related inflammation

Mechanisms for cancer-related inflammation remain to be fully elucidated. Non-apoptotic functions of Fas signaling have been proposed to play an important role in promoting tumor progression. It has yet to be determined if targeting Fas signaling can control tumor progression through suppression of cancer-related inflammation. In the current study we found that breast cancer cells with constitutive Fas expression were resistant to apoptosis induction by agonistic anti-Fas antibody (Jo2) ligation or Fas ligand cross-linking. Higher expression of Fas in human breast cancer tissue has been significantly correlated with poorer prognosis in breast cancer patients. To determine whether blockade of Fas signaling in breast cancer could suppress tumor progression, we prepared an orthotopic xenograft mouse model with mammary cancer cells 4T1 and found that blockade of Fas signaling in 4T1 cancer cells markedly reduced tumor growth, inhibited tumor metastasis in vivo, and prolonged survival of tumor-bearing mice. Mechanistically, blockade of Fas signaling in cancer cells significantly decreased systemic or local recruitment of myeloid derived suppressor cells (MDSCs) in vivo. Furthermore, blockade of Fas signaling markedly reduced IL-6, prostaglandin E2 production from breast cancer cells by impairing p-p38, and activity of the NFκB pathway. In addition, administration of a COX-2 inhibitor and anti-IL-6 antibody significantly reduced MDSC accumulation in vivo. Therefore, blockade of Fas signaling can suppress breast cancer progression by inhibiting proinflammatory cytokine production and MDSC accumulation, indicating that Fas signaling-initiated cancer-related inflammation in breast cancer cells may be a potential target for treatment of breast cancer.

Life in the Fas lane: differential outcomes of Fas signaling

Fas, also known as CD95 or APO-1, is a member of the tumor necrosis factor/nerve growth factor superfamily. Although best characterized in terms of its apoptotic function, recent studies have identified several other cellular responses emanating from Fas. These responses include migration, invasion, inflammation, and proliferation. In this review, we focus on the diverse cellular outcomes of Fas signaling and the molecular switches identified to date that regulate its pro- and anti-apoptotic functions. Such switches occur at different levels of signal transduction, ranging from the receptor through to cross-talk with other signaling pathways. Factors identified to date including other extracellular signals, proteins recruited to the death-inducing signaling complex, and the availability of different intracellular components of signal transduction pathways. The success of therapeutically targeting Fas will require a better understanding of these pathways, as well as the regulatory mechanisms that determine cellular outcome following receptor activation.

Opioid administration following spinal cord injury: implications for pain and locomotor recovery

Approximately one-third of people with a spinal cord injury (SCI) will experience persistent neuropathic pain following injury. This pain negatively affects quality of life and is difficult to treat. Opioids are among the most effective drug treatments, and are commonly prescribed, but experimental evidence suggests that opioid treatment in the acute phase of injury can attenuate recovery of locomotor function. In fact, spinal cord injury and opioid administration share several common features (e.g. central sensitization, excitotoxicity, aberrant glial activation) that have been linked to impaired recovery of function, as well as the development of pain. Despite these effects, the interactions between opioid use and spinal cord injury have not been fully explored. A review of the literature, described here, suggests that caution is warranted when administering opioids after SCI. Opioid administration may synergistically contribute to the pathology of SCI to increase the development of pain, decrease locomotor recovery, and leave individuals at risk for infection. Considering these negative implications, it is important that guidelines are established for the use of opioids following spinal cord and other central nervous system injuries.

Genome-wide gene expression profiling of stress response in a spinal cord clip compression injury model

Background

The aneurysm clip impact-compression model of spinal cord injury (SCI) is a standard injury model in animals that closely mimics the primary mechanism of most human injuries: acute impact and persisting compression. Its histo-pathological and behavioural outcomes are extensively similar to human SCI. To understand the distinct molecular events underlying this injury model we analyzed global mRNA abundance changes during the acute, subacute and chronic stages of a moderate to severe injury to the rat spinal cord.

Results

Time-series expression analyses resulted in clustering of the majority of deregulated transcripts into eight statistically significant expression profiles. Systematic application of Gene Ontology (GO) enrichment pathway analysis allowed inference of biological processes participating in SCI pathology. Temporal analysis identified events specific to and common between acute, subacute and chronic time-points. Processes common to all phases of injury include blood coagulation, cellular extravasation, leukocyte cell-cell adhesion, the integrin-mediated signaling pathway, cytokine production and secretion, neutrophil chemotaxis, phagocytosis, response to hypoxia and reactive oxygen species, angiogenesis, apoptosis, inflammatory processes and ossification. Importantly, various elements of adaptive and induced innate immune responses span, not only the acute and subacute phases, but also persist throughout the chronic phase of SCI. Induced innate responses, such as Toll-like receptor signaling, are more active during the acute phase but persist throughout the chronic phase. However, adaptive immune response processes such as B and T cell activation, proliferation, and migration, T cell differentiation, B and T cell receptor-mediated signaling, and B cell- and immunoglobulin-mediated immune response become more significant during the chronic phase.

Conclusions

This analysis showed that, surprisingly, the diverse series of molecular events that occur in the acute and subacute stages persist into the chronic stage of SCI. The strong agreement between our results and previous findings suggest that our analytical approach will be useful in revealing other biological processes and genes contributing to SCI pathology.

Fas signal promotes the immunosuppressive function of regulatory dendritic cells via the ERK/β-catenin pathway

Dendritic cells (DCs) play important roles in the initiation of immune response and also in the maintenance of immune tolerance. Now, many kinds of regulatory DCs with different phenotypes have been identified to suppress immune response and contribute to the control of autoimmune diseases. However, the mechanisms by which regulatory DCs can be regulated to exert the immunosuppressive function in the immune microenvironment remain to be fully investigated. In addition, how T cells, once activated, can feedback affect the function of regulatory DCs during immune response needs to be further identified. We previously identified a unique subset of CD11b(hi)Ia(low) regulatory DCs, differentiated from mature DCs or hematopoietic stem cells under a stromal microenvironment in spleen and liver, which can negatively regulate immune response in a feedback way. Here, we show that CD11b(hi)Ia(low) regulatory DCs expressed high level of Fas, and endothelial stromal cell-derived TGF-β could induce high expression of Fas on regulatory DCs via ERK activation. Fas ligation could promote regulatory DCs to inhibit CD4(+) T cell proliferation more significantly. Furthermore, Fas ligation preferentially induced regulatory DCs to produce IL-10 and IP-10 via ERK-mediated inactivation of GSK-3 and subsequent up-regulation of β-catenin. Interestingly, activated T cells could promote regulatory DCs to secrete more IL-10 and IP-10 partially through FasL. Therefore, our results demonstrate that Fas signal, at least from the activated T cells, can promote the immunosuppressive function of Fas-expressing regulatory DCs, providing a new manner for the regulatory DCs to regulate adaptive immunity.

Age-dependent changes in FasL (CD95L) modulate macrophage function in a model of age-related macular degeneration

PURPOSE

We examined the effect of aging on Fas ligand (FasL) function in a mouse model of choroidal neovascularization (CNV).

METHODS

Young and aged mice were laser treated to induce CNV. Bone marrow chimeras were performed between young and aged mice. FasL protein expression was examined in the eye and soluble FasL (sFasL) was measured in the blood. Young and aged mice were treated with a matrix metalloprotease (MMP) inhibitor and systemic sFasL was neutralized by antibody treatment. Macrophages from young and aged mice were tested for sFasL-mediated cytokine production and migration.

RESULTS

The elevated CNV response observed with aging was dependent on bone marrow-derived cells. FasL expression in the eye was increased with age, but decreased following laser treatment. Aged mice had higher levels of sFasL in the blood compared to young mice. Systemic treatment with an MMP inhibitor decreased bloodborne sFasL, and reduced CNV in young and aged mice. Systemic neutralization of sFasL reduced CNV only in aged mice. sFasL increased cytokine production in aged macrophages and proangiogenic M2 macrophages. Aged M2 macrophages had elevated Fas (CD95) expression and displayed increased migration in response to sFasL compared to M1 macrophages derived from young animals.

CONCLUSIONS

Age modulates FasL function where increased MMP cleavage leads to a loss of function in the eye. The released form of FasL (sFasL) preferentially induces the migration of proangiogenic M2 macrophages into the laser lesions and increases proangiogenic cytokines promoting CNV. FasL may be a viable target for therapeutic intervention in aged-related neovascular disease.

The benefits and detriments of macrophages/microglia in models of multiple sclerosis

The central nervous system (CNS) is immune privileged with access to leukocytes being limited. In several neurological diseases, however, infiltration of immune cells from the periphery into the CNS is largely observed and accounts for the increased representation of macrophages within the CNS. In addition to extensive leukocyte infiltration, the activation of microglia is frequently observed. The functions of activated macrophages/microglia within the CNS are complex. In three animal models of multiple sclerosis (MS), namely, experimental autoimmune encephalomyelitis (EAE) and cuprizone- and lysolecithin-induced demyelination, there have been many reported detrimental roles associated with the involvement of macrophages and microglia. Such detriments include toxicity to neurons and oligodendrocyte precursor cells, release of proteases, release of inflammatory cytokines and free radicals, and recruitment and reactivation of T lymphocytes in the CNS. Many studies, however, have also reported beneficial roles of macrophages/microglia, including axon regenerative roles, assistance in promoting remyelination, clearance of inhibitory myelin debris, and the release of neurotrophic factors. This review will discuss the evidence supporting the detrimental and beneficial aspects of macrophages/microglia in models of MS, provide a discussion of the mechanisms underlying the dichotomous roles, and describe a few therapies in clinical use in MS that impinge on the activity of macrophages/microglia.

Innate immunity in the Grid2Lc/+ mouse model of cerebellar neurodegeneration: glial CD95/CD95L plays a non-apoptotic role in persistent neuron loss-associated inflammatory reactions in the cerebellum

Background

There is growing evidence that the death receptor CD95 has a wider role in non-apoptotic functions. In the brain, it may contribute to neural death and to the associated inflammatory reaction via a non-apoptotic pathway. Brain injury triggers an inflammatory reaction in which the CD95/CD95L system acts principally through peripheral cells recruited to the lesion. In cases of inflammation within the brain, with no blood–brain barrier leakage, the role of the CD95/CD95L system is thus unclear. We investigated the possible role of CD95 and CD95L in such conditions, by studying the relationships between glial cell activation, neuron death and CD95/CD95L expression in the cerebellum of the Lurcher (Grid2^Lc/+) mutant mouse, a model of cerebellar neurodegeneration.

Methods

Glial cells in slices of wild-type and Lurcher mouse cerebella were observed by light microscopy at various ages overlapping periods of neuron loss and of pre- and post-neurodegeneration. Subcellular organization was studied by electron microscopy. We assessed CD95 levels by western blotting, RT-PCR and glial cell cultures. The levels of CD95L and IL-6 were studied by ELISA and a biological assay, respectively.

Results

In the Grid2^Lc/+cerebellum, neuron loss triggers a typical, but abnormally persistent, inflammatory reaction. We identified two phases of astrogliosis: an early burst of large glial cell activation, peaking at postnatal days 25 to 26, coinciding with peak cerebellar neuron loss, followed by a long period of slow decline indicating that the strength of the glial reaction is modulated by neuron mortality rates. Comparisons of time-courses of glial cell activation, cytokine production and neuron loss revealed that the number of surviving neurons decreased as CD95 increased. Thus, CD95 cannot be directly involved in neuron death, and its role must be limited to a contribution to the inflammatory reaction. The upregulation of CD95 likely on astrocytes coincides with increases in the levels of IL-6, a cytokine produced principally by astrocytes, and soluble CD95L.

Conclusions

These results suggest that CD95 and soluble CD95L contribute, via non-apoptotic signaling, to the inflammatory reaction initiated early in neuron death within the Grid2^Lc/+ cerebellum.

CD95 in cancer: tool or target?

The role of CD95 (Fas/Apo1) in cancer has been a matter of debate for over 30 years. First discovered as an apoptosis-inducing molecule, CD95 soon emerged as a potential anticancer therapy. Yet accumulating evidence indicates a profound role for CD95 in alternative nonapoptotic signaling pathways that increase tumorigenesis. This fact challenges the initial clinical idea of using CD95 as a 'tumor killer' while setting the stage for clinical studies targeting the nonapoptotic signaling branch of CD95. This review summarizes the findings surrounding manipulation of the CD95 pathway for cancer therapy, considering how one receptor can both promote and prevent cell growth.

Myeloid-derived suppressor cells suppress antitumor immune responses through IDO expression and correlate with lymph node metastasis in patients with breast cancer

Myeloid-derived suppressor cells (MDSCs) represent heterogeneous immunosuppressive cells in multiple cancer types and display potent immunosuppressive activity on T cells. We have shown the increased expression of IDO in breast cancer. Because IDO plays a pivotal role in immune tolerance via suppressing T cell function, the aim of this study was to investigate the expression of IDO in MDSCs in breast cancer and its role in MDSC-mediated inhibition of immune surveillance. The proportion of MDSCs with the phenotype of CD45(+)CD13(+)CD33(+)CD14(-)CD15(-) significantly increased in primary cancer tissues and patients' peripheral blood. IDO expression was significantly upregulated in MDSCs isolated from fresh breast cancer tissues (fresh MDSCs [fMDSCs]), which correlated with increased infiltration of Foxp3(+) regulatory T cells in tumors and lymph node metastasis in patients. fMDSCs inhibited IL-2 and anti-CD3/CD28 mAb-induced T cell amplification and Th1 polarization but stimulated apoptosis in T cells in an IDO-dependent manner. CD33(+) progenitors isolated from healthy donors' umbilical cord blood were cocultured with breast cancer cell line MDA-MB-231 cells to induce MDSCs. IDO expression was upregulated in induced MDSCs, which required phosphorylation of STAT3, but not STAT1. IDO was required for induced MDSCs' immunosuppressive activity on T cells, which was blocked by IDO inhibitor 1-methyl-L-tryptophan or STAT3 antagonist JSI-124. Consistently, increased STAT3 phosphorylation level was found in fMDSCs. Together, our findings suggest that STAT3-dependent IDO expression mediates immunosuppressive effects of MDSCs in breast cancer. Thus, inhibition of MDSC-induced T cell suppression by blocking IDO may represent a previously unrecognized mechanism underlying immunotherapy for breast cancer.

The arthritis severity locus Cia5a regulates the expression of inflammatory mediators including Syk pathway genes and proteases in pristane-induced arthritis

Background

Cia5a is a locus on rat chromosome 10 that regulates disease severity and joint damage in two models of rheumatoid arthritis, collagen- and pristane-induced arthritis (PIA). In this study, we aimed to identify cellular and molecular processes regulated by Cia5a using microarray-based gene expression analysis of synovial tissues from MHC identical DA (severe erosive disease) and DA.F344(Cia5a) congenics (mild non-erosive disease) rats.

Results

Synovial tissues from six DA and eight DA.F344(Cia5a) rats were analyzed 21 days after the induction of PIA using the Illumina RatRef-12 BeadChip (21,922 genes) and selected data confirmed with qPCR. There was a significantly increased expression of pro-inflammatory mediators such as Il1b (5-fold), Il18 (3.9-fold), Cxcl1 (10-fold), Cxcl13 (7.5-fold) and Ccl7 (7.9-fold), and proteases like Mmp3 (23-fold), Mmp9 (32-fold), Mmp14 (4.4-fold) and cathepsins in synovial tissues from DA, with reciprocally reduced levels in congenics. mRNA levels of 47 members of the Spleen Tyrosine Kinase (Syk) pathway were significantly increased in DA synovial tissues compared with DA.F344(Cia5a), and included Syk (5.4-fold), Syk-activating receptors and interacting proteins, and genes regulated by Syk such as NFkB, and NAPDH oxidase complex genes. Nuclear receptors (NR) such as Rxrg, Pparg and Rev-erba were increased in the protected congenics, and so was the anti-inflammatory NR-target gene Scd1 (54-fold increase). Tnn (72-fold decrease) was the gene most significantly increased in DA.

Conclusions

Analyses of gene expression in synovial tissues revealed that the arthritis severity locus Cia5a regulates the expression of key mediators of inflammation and joint damage, as well as the expression of members of the Syk pathway. This expression pattern correlates with disease severity and joint damage and along with the gene accounting for Cia5a could become a useful biomarker to identify patients at increased risk for severe and erosive disease. The identification of the gene accounting for Cia5a has the potential to generate a new and important target for therapy and prognosis.

Signaling lymphocyte activation molecule regulates development of colitis in mice

BACKGROUND & AIMS

Signaling lymphocyte activation molecule (Slamf)1 is a co-stimulatory receptor on T cells and regulates cytokine production by macrophages and dendritic cells. Slamf1 regulates microbicidal mechanisms in macrophages, therefore we investigated whether the receptor affects development of colitis in mice.

METHODS

We transferred CD45RB(hi) CD4(+) T cells into Rag(-/-) or Slamf1(-/-)Rag(-/-) mice to induce colitis. We also induced colitis by injecting mice with an antibody that activates CD40. We determined the severity of enterocolitis based on disease activity index, histology scores, and levels of cytokine production, and assessed the effects of antibodies against Slamf1 on colitis induction. We quantified migration of monocytes and macrophage to inflamed tissues upon induction of colitis or thioglycollate-induced peritonitis and in response to tumor necrosis factor-α in an air-pouch model of leukocyte migration.

RESULTS

Colitis was reduced in Slamf1(-/-)Rag(-/-) mice, compared with Rag(-/-) mice, after transfer of CD45RB(hi) CD4(+) T cells or administration of the CD40 agonist. The numbers of monocytes and macrophages were reduced in inflamed tissues of Slamf1(-/-)Rag(-/-) mice, compared with Rag(-/-) mice, after induction of colitis and other inflammatory disorders. An antibody that inhibited Slamf1 reduced the level of enterocolitis in Rag(-/-) mice.

CONCLUSIONS

Slamf1 contributes to the development of colitis in mice. It appears to indirectly regulate the appearance of monocytes and macrophages in inflamed intestinal tissues. Antibodies that inhibit Slamf1 reduce colitis in mice, so human SLAMF1 might be a therapeutic target for inflammatory bowel disease.

Increase in soluble CD95L during subacute phases after human spinal cord injury: a potential therapeutic target

STUDY DESIGN

A pilot study measuring the levels of serum-soluble CD95 ligand (CD95L) in eight spinal cord-injured patients.

OBJECTIVES

To determine the soluble concentration of CD95L in spinal cord injury (SCI) patients after trauma.

METHODS

We collected blood samples from eight patients with acute traumatic SCI. Soluble CD95L serum levels were determined using an enzyme-linked immunosorbent assay. American Spinal Injury Association (ASIA) was determined according to ASIA classification. The patients were monitored, and venous blood was drawn after arrival at the hospital on the 1st and 3rd day and during the 1st, 2nd, 4th, 8th and 12th weeks after trauma.

RESULTS

The average patient age was 48.1 years (18-86 years). Three patients were paraplegic (two incomplete, one complete), five were quadriplegic (one complete, four incomplete). The serum concentration of soluble CD95L (sCD95L) decreased during the 1st week (41 ng(- l)) and increased after the 2nd week in all eight patients. It peaked during the 4th week (68.5 ng (- l)) and reached a plateau during the 12th week (76.2 ng (- l)). There are many possible explanations for not being able to detect a statistical significance, one of course being the small sample size.

CONCLUSION

Promising results for anti-CD95L therapy have already been documented in lab studies with rodents. Anti-CD95L blocks the pro-apoptotic and proinflammatory activity of membrane-bound CD95L during the acute phase of SCI. We observed that sCD95L levels are elevated during the subacute and intermediate phases of SCI. It would be of great interest to study a larger group of patients to determine whether higher sCD95 levels are correlated with improved or impaired neurological outcome or with increasing levels of autoimmune components in peripheral blood.

Precise mapping of the CD95 pre-ligand assembly domain

Pre-association of CD95 at the plasma membrane is mandatory for efficient death receptor signaling. This homotrimerization occurs through self-association of an extracellular domain called the pre-ligand assembly domain (PLAD). Using novel molecular and cellular tools, we confirmed that CD95-PLAD is necessary to promote CD95 multimerization and plays a pivotal role in the transmission of apoptotic signals. However, while a human CD95 mutant deleted of the previously described PLAD domain (amino acids 1 to 66) fails to interact with its wild-type counterpart and trigger autonomous cell death, deletion of amino acids 1 to 42 does not prevent homo- or hetero (human/mouse)-oligomerization of CD95, and thus does not alter transmission of the apoptotic signal. Overall, these findings indicate that the region between amino acids 43 to 66 corresponds to the minimal motif involved in CD95 homotypic interaction and is necessary to convey an efficient apoptotic signal. Interfering with this PLAD may represent a new therapeutic strategy for altering CD95-induced apoptotic and non-apoptotic signals.

Neutrophil expression of Fas ligand and perforin directs effector CD8 T cell infiltration into antigen-challenged skin

Contact hypersensitivity (CHS) is a T cell response to hapten skin challenge of sensitized individuals proposed to be mediated by hapten-primed CD8 cytolytic T cells. Effector CD8 T cell recruitment into hapten challenge sites to elicit CHS requires prior CXCL1- and CXCL2-mediated neutrophil infiltration into the site. We investigated whether neutrophil activities directing hapten-primed CD8 T cell skin infiltration in response to 2,4-dinitro-1-fluorobenzene (DNFB) required Fas ligand (FasL) and perforin expression. Although DNFB sensitization of gld/perforin-/- mice induced hapten-specific CD8 T cells producing IFN-γ and IL-17, these T cells did not infiltrate the DNFB challenge site to elicit CHS but did infiltrate the challenge site and elicit CHS when transferred to hapten-challenged naive wild-type recipients. Hapten-primed wild-type CD8 T cells, however, did not elicit CHS when transferred to naive gld/perforin-/- recipients. Wild-type bone marrow neutrophils expressed FasL and perforin, and when transferred to sensitized gld/perforin-/- mice, they restored hapten-primed CD8 T cell infiltration into the challenge site and CHS. The FasL/perforin-mediated activity of wild-type neutrophils induced the expression of T cell chemoattractants, CCL1, CCL2, and CCL5, within the hapten-challenged skin. These results indicate FasL/perforin-independent functions of hapten-primed CD8 T cells in CHS and identify new functions for neutrophils in regulating effector CD8 T cell recruitment and immune responses in the skin.

Activated T cell exosomes promote tumor invasion via Fas signaling pathway

Activated T cells release bioactive Fas ligand (FasL) in exosomes, which subsequently induce self-apoptosis of T cells. However, their potential effects on cell apoptosis in tumors are still unknown. In this study, we purified exosomes expressing FasL from activated CD8(+) T cell from OT-I mice and found that activated T cell exosomes had little effect on apoptosis and proliferation of tumor cells but promoted the invasion of B16 and 3LL cancer cells in vitro via the Fas/FasL pathway. Activated T cell exosomes increased the amount of cellular FLICE inhibitory proteins and subsequently activated the ERK and NF-κB pathways, which subsequently increased MMP9 expression in the B16 murine melanoma cells. In a tumor-invasive model in vivo, we observed that the activated T cell exosomes promoted the migration of B16 tumor cells to lung. Interestingly, pretreatment with FasL mAb significantly reduced the migration of B16 tumor cells to lung. Furthermore, CD8 and FasL double-positive exosomes from tumor mice, but not normal mice, also increased the expression of MMP9 and promoted the invasive ability of B16 murine melanoma and 3LL lung cancer cells. In conclusion, our results indicate that activated T cell exosomes promote melanoma and lung cancer cell metastasis by increasing the expression of MMP9 via Fas signaling, revealing a new mechanism of tumor immune escape.

CD95-mediated cell signaling in cancer: mutations and post-translational modulations

Apoptosis has emerged as a fundamental process important in tissue homeostasis, immune response, and during development. CD95 (also known as Fas), a member of the tumor necrosis factor receptor (TNF-R) superfamily, has been initially cloned as a death receptor. Its cognate ligand, CD95L, is mainly found at the plasma membrane of activated T-lymphocytes and natural killer cells where it contributes to the elimination of transformed and infected cells. According to its implication in the immune homeostasis and immune surveillance, and since several malignant cells of various histological origins exhibit loss-of-function mutations, which cause resistance towards the CD95-mediated apoptotic signal, CD95 has been classified as a tumor suppressor gene. Nevertheless, this assumption has been recently challenged, as in certain pathophysiological contexts, CD95 engagement transmits non-apoptotic signals that promote inflammation, carcinogenesis or liver/peripheral nerve regeneration. The focus of this review is to discuss these apparent contradictions of the known function(s) of CD95.

CD95 signaling in colorectal cancer

CD95 and its ligand (CD95L) are widely expressed in colorectal tumors, but their role in shaping tumor behavior is unclear. CD95 activation on tumor cells can lead to apoptosis, while CD95L attracts neutrophils, suggesting a function in tumor suppression. However, CD95 can also promote tumorigenesis, at least in part by activating non-apoptotic signaling pathways that stimulate tumor cell proliferation, invasion and survival. In addition, CD95 signaling in stromal cells and tumor-infiltrating inflammatory cells has to be taken into account when addressing the function of CD95 and its ligand in colorectal tumor biology. We present a model in which the tumor-suppressing and tumor-promoting activities of CD95/CD95L together determine colorectal tumor behavior. We also discuss how these multiple activities are changing our view of CD95 and CD95L as potential therapeutic targets in the treatment of colorectal cancer. We conclude that locking CD95 in apoptosis-mode may be a more promising anti-cancer strategy than simply inhibiting or stimulating CD95.

Age-related differences in cellular and molecular profiles of inflammatory responses after spinal cord injury

Previous experimental and clinical studies have suggested that the behavioral and pathological outcomes of spinal cord injury (SCI) are affected by the individual's age at the time of injury. However, the underlying mechanism responsible for these differences remains elusive because it is difficult to match injuries of similar severities between young and adult animals due to differences in the sizes of their respective spinal cords. In this study, the spinal cord size-matched young (4-week-old) and adult (10-week-old) mice were compared to evaluate their locomotor functions and inflammatory cellular/molecular responses after standardized contusion SCI. During the acute phase of SCI, young mice showed better functional recovery and lower pro-inflammatory cytokines/chemokines compared to adult mice. Flow-cytometric analysis revealed that the time courses of leukocyte infiltration were comparable between both groups, while the number of infiltrating neutrophils significantly decreased from 6 h after SCI in young mice. By combining flow-cytometric isolation and gene expression analysis of each inflammatory cell fraction, we found that microglial cells immediately initiate the production of several cytokines in response to SCI, which serve as major sources of IL-6, TNFa, and CXCL1 in injured spinal cord. Interestingly, the secretion of pro-inflammatory cytokines/chemokines but not anti-inflammatory cytokines by microglia was significantly lower in young mice compared to that in adult mice at 3 h after SCI, which will be attributed to the attenuation of the subsequent neutrophil infiltration. These results highlight age-related differences in pro-inflammatory properties of microglial cells that contribute to the amplification of detrimental inflammatory responses after SCI.

Matrix metalloproteinase-9 and stromal cell-derived factor-1 act synergistically to support migration of blood-borne monocytes into the injured spinal cord

The infiltration of monocytes into the lesioned site is a key event in the inflammatory response after spinal cord injury (SCI). We hypothesized that the molecular events governing the infiltration of monocytes into the injured cord involve cooperativity between the upregulation of the chemoattractant stromal cell-derived factor-1 (SDF-1)/CXCL12 in the injured cord and matrix metalloproteinase-9 (MMP-9/gelatinase B), expressed by infiltrating monocytes. SDF-1 and its receptor CXCR4 mRNAs were upregulated in the injured cord, while macrophages immunoexpressed CXCR4. When mice, transplanted with bone marrow cells from green fluorescent protein (GFP) transgenic mice, were subjected to SCI, GFP+ monocytes infiltrated the cord and displayed gelatinolytic activity. In vitro studies confirmed that SDF-1α, acting through CXCR4, expressed on bone marrow-derived macrophages, upregulated MMP-9 and stimulated MMP-9-dependent transmigration across endothelial cell monolayers by 2.6-fold. There was a reduction in F4/80+ macrophages in spinal cord-injured MMP-9 knock-out mice (by 36%) or wild-type mice, treated with the broad-spectrum MMP inhibitor GM6001 (by 30%). Mice were adoptively transferred with myeloid cells and treated with the MMP-9/-2 inhibitor SB-3CT, the CXCR4 antagonist AMD3100, or a combination of both drugs. While either drug resulted in a 28-30% reduction of infiltrated myeloid cells, the combined treatment resulted in a 45% reduction, suggesting that SDF-1 and MMP-9 function independently to promote the trafficking of myeloid cells into the injured cord. Collectively, these observations suggest a synergistic partnership between MMP-9 and SDF-1 in facilitating transmigration of monocytes into the injured spinal cord.

Fas/FasL-mediated apoptosis and inflammation are key features of acute human spinal cord injury: implications for translational, clinical application

The Fas/FasL system plays an important role in apoptosis, the inflammatory response and gliosis in a variety of neurologic disorders. A better understanding of these mechanisms could lead to effective therapeutic strategies following spinal cord injury (SCI). We explored these mechanisms by examining molecular changes in postmortem human spinal cord tissue from cases with acute and chronic SCI. Complementary studies were conducted using the in vivo Fejota™ clip compression model of SCI in Fas-deficient B6.MRL-Fas-lpr (lpr) and wild-type (Wt) mice to test Fas-mediated apoptosis, inflammation, gliosis and axonal degeneration by immunohistochemistry, Western blotting, gelatin zymography and ELISA with Mouse 32-plex cytokine/chemokine panel bead immunoassay. We report novel evidence that shows that Fas-mediated apoptosis of neurons and oligodendrocytes occurred in the injury epicenter in all cases of acute and subacute SCI and not in chronic SCI or in control cases. We also found significantly reduced apoptosis, expression of GFAP, NF-κB, p-IKappaB and iba1, increased number of CD4 positive T cells and MMP2 expression and reduced neurological dysfunction in lpr mice when compared with Wt mice after SCI. We found dramatically reduced inflammation and cytokines and chemokine expression in B6.MRL-Fas-lpr mice compared to Wt mice after SCI. In conclusion, we report multiple lines of evidence that Fas/FasL activation plays a pivotal role in mediating apoptosis, the inflammatory response and neurodegeneration after SCI, providing a compelling rationale for therapeutically targeting Fas in human SCI.

Spleen tyrosine kinase mediates BEAS-2B cell migration and proliferation and human rhinovirus-induced expression of vascular endothelial growth factor and interleukin-8

Spleen tyrosine kinase (Syk) is an immunoregulatory tyrosine kinase that was identified originally in leukocytes. It is a key regulator of innate immunity as well as hematopoietic cell differentiation and proliferation. A role for Syk in regulating normal cellular functions in nonhematopoietic cells is increasingly recognized. We have shown previously robust Syk expression in airway epithelium, where it regulates the early inflammatory response to human rhinovirus (HRV) infections, and HRV cell entry by clathrin-mediated endocytosis. To test the hypothesis that Syk plays a role in modulating airway epithelial cell proliferation, migration, and production of vascular endothelial growth factor and interleukin-8, we studied the BEAS-2B human bronchial epithelial cell line and primary human airway epithelia from normal and asthmatic donors using Syk-specific pharmacologic inhibitors and small interfering RNA. Using an in vitro "wounding" model, we demonstrated significant impairment of "wound" closure after treatment with the Syk inhibitors N4-(2,2-dimethyl-3-oxo-4H-pyrid[1,4]oxazin-6-yl)-5-fluoro-N2-(3,4,5-trimethoxyphenyl)-2,4-pyrimidinediamine (R406) and 2-[7-(3,4-dimethoxyphenyl)-imidazo[1,2-c]pyrimidin-5-ylamino]-nicotinamide dihydrochloride (BAY61-3606), overexpression of the kinase-inactive Syk(K396R) mutant, and Syk knockdown by small interfering RNA. HRV infection also impaired wound healing, an effect that was partly Syk-dependent because wound healing was impaired further when HRV infection occurred in the presence of Syk inhibition. Further investigation of potential regulatory mechanisms revealed that inhibition of Syk suppressed HRV-induced vascular endothelial growth factor expression while promoting the activation of caspase-3, a mediator of epithelial cell apoptosis. Together, these results indicate that Syk plays a role in promoting epithelial cell proliferation and migration, while mitigating the effects of apoptosis.

Induced Syk deletion leads to suppressed allergic responses but has no effect on neutrophil or monocyte migration in vivo

The spleen tyrosine kinase (Syk) is a key mediator of immunoreceptor signaling in immune cells. Thus, interfering with the function of Syk by genetic deletion or pharmacological inhibition might influence a variety of allergic and autoimmune processes. Since conventional Syk knockout mice are not viable, studies addressing the effect of Syk deletion in adult animals have been limited. To further explore functions of Syk in animal models of allergy and to shed light on the role of Syk in the in vivo migration of neutrophils and monocytes, we generated inducible Syk knockout mice. These mice harbor a floxed Syk gene and a tamoxifen-inducible Cre recombinase under the control of the ubiquitously active Rosa26-promoter. Thus, treatment of mice with tamoxifen leads to the deletion of Syk in all organs. Syk-deleted mice were analyzed in mast cell-dependent models and in models focusing on neutrophil and monocyte migration. We show that Syk deletion in adult mice reduces inflammatory responses in mast cell-driven animal models of allergy and asthma but has no effect on the migration of neutrophils and monocytes. Therefore, the inducible Syk knockout mice presented here provide a valuable tool to further explore the role of Syk in disease-related animal models.

Involvement of the Syk-mTOR pathway in follicular lymphoma cell invasion and angiogenesis

Follicular lymphoma (FL) is the second-most common non-Hodgkin's lymphoma. The disease affects the lymph nodes, and 50% of patients present with bone marrow infiltration; however, the mechanisms involved in dissemination of the disease are not yet known. We previously reported that FL cells display an overexpression of Syk, a tyrosine kinase involved in many cellular processes including cell migration. Therefore, we sought to explore its role in the invasive process. Here, we show that FL patients display higher matrix metalloproteinase (MMP)-9 and vascular endothelial growth factor (VEGF) levels than healthy donors. Moreover, using Syk small interfering RNA and the Syk inhibitor R406, we demonstrate that, in FL cells, Syk is involved in the regulation of MMP-9 and VEGF expression, and that invasion and angiogenesis is mediated through a phosphatidylinositol-3 kinase (PI3K)-mammalian target of rapamycin module. Finally, using a FL xenograft mouse model we observe that fostamatinib (R788), inhibits MMP-9 expression and angiogenesis in vivo. Altogether, this study provides strong evidence that Syk represents an encouraging therapeutic target in FL and suggests the potential use of fostamatinib as an anti-invasive and anti-angiogenic drug.

Mice with defective Fas ligand are protected from crescentic glomerulonephritis

Fas ligand is a well-known inducer of apoptosis in cells expressing its receptor Fas; it also prevents autoimmunity by inducing apoptosis of activated T cells. However, Fas ligand also mediates non-apoptotic functions involving inflammatory cell migration and cytokine responses. We sought here to study the role of Fas ligand in nephrotoxic nephritis, a model of crescentic glomerulonephritis, using generalized lymphoproliferative disorder (GLD) mice on a C57BL/6 background, which have defective Fas ligand and display only mild autoimmunity. These mice were significantly protected from glomerular crescent formation, glomerular thrombosis, renal impairment, and albuminuria 15 days after the induction of glomerulonephritis in comparison with wild-type mice. There were a reduced number of apoptotic cells in the glomeruli of nephritic GLD mice but no defect in their antibody responses or splenocyte proliferation at 15 days following the induction of glomerulonephritis. Bone marrow transplantation from wild-type mice restored disease susceptibility to GLD mice; however, wild-type mice were not protected when transplanted with bone marrow from GLD mice. Mesangial cells express Fas ligand in vitro, and these cells isolated from GLD mice produced lower amounts of monocyte chemoattractive protein-1 following interleukin-1 stimulation compared with cells from wild-type mice. Thus, Fas ligand-defective mice are protected from nephrotoxic nephritis, a disease in which both circulating and intrinsic renal cells appear to have a role.

The death receptor CD95 activates the cofilin pathway to stimulate tumour cell invasion

The death receptor CD95 promotes apoptosis through well-defined signalling pathways. In colorectal cancer cells, CD95 primarily stimulates migration and invasion through pathways that are incompletely understood. Here, we identify a new CD95-activated tyrosine kinase pathway that is essential for CD95-stimulated tumour cell invasion. We show that CD95 promotes Tyr 783 phosphorylation of phospholipase C-γ1 through the platelet-derived growth factor receptor-β, resulting in ligand-stimulated phosphatidylinositol (4,5)-bisphosphate (PIP(2)) hydrolysis. PIP(2) hydrolysis liberates the actin-severing protein cofilin from the plasma membrane to initiate cortical actin remodelling. Cofilin activation is required for CD95-stimulated formation of membrane protrusions and increased tumour cell invasion.

Prevention of both neutrophil and monocyte recruitment promotes recovery after spinal cord injury

Strategies that block infiltration of leukocytes into the injured spinal cord improve sparing of white matter and neurological recovery. In this article, we examine the dependency of recovery on hematogenous depletion of neutrophils and monocytes. Mice were depleted of neutrophils or monocytes by systemic administration of anti-Ly6G or clodronate-liposomes. A third group was depleted of both subsets. Neurological improvement, based on a battery of tests of performance, and white matter sparing, occurred only in animals depleted of both neutrophils and monocytes. We also attempted to define the nature of the environment that was favorable to recovery. Hemeoxygenase-1 and malondialdehyde, markers of oxidative stress and lipid peroxidation, respectively, were reduced to similar levels in animals depleted of both neutrophils and monocytes, or only monocytes, but remained elevated in the group only depleted of neutrophils. Matrix metalloproteinase-9, a protease involved in early damage, was most strongly reduced in animals depleted of both leukocyte subsets. Finally, disruption of the blood-spinal cord barrier and abnormal nonheme iron accumulation were reduced only in animals depleted of both neutrophils and monocytes. Together, these findings indicate cooperation between neutrophils and monocytes in mediating early pathogenesis in the contused spinal cord and defining long-term neurological recovery.

Attenuated neurological deficit, cell death and lesion volume in Fas-mutant mice is associated with altered neuroinflammation following traumatic brain injury

Progressive neurodegeneration following traumatic brain injury (TBI) involves the Fas and TNF-receptor1 protein systems which have been implicated in mediating delayed cell death. In this study, we used two approaches to assess whether inhibition of these pathways reduced secondary brain damage and neurological deficits after TBI. Firstly, we investigated whether the expression of non-functional Fas in lpr mice subjected to TBI altered tissue damage and neurological outcome. Compared to wild-type, lpr mice showed improved neurological deficit (p=0.0009), decreased lesion volume (p=0.017), number of TUNEL+ cells (p=0.011) and caspase-3+ cells (p=0.007). Changes in cellular inflammation and cytokine production were also compared between mouse strains. Accumulation of macrophages/microglia occurred earlier in lpr mice, likely due to enhanced production of the chemotactic mediators IL-12(p40) and MCP-1 (p<0.05). Cortical production of IL-1α and IL-6 increased after injury to a similar extent regardless of strain (p<0.05), while TNF and G-CSF were significantly higher in lpr animals (p<0.05). Secondly, we assessed whether therapeutic inhibition of FasL and TNF via intravenous injection of neutralizing antibodies in wild-type mice post-TBI could reproduce the beneficial effects observed in lpr animals. No differences were found with this approach in animals treated with anti-FasL and anti-TNF antibodies alone or the combination of both. Altogether, reduced neurological deficits and lesion volume in lpr mice was associated with altered cellular and humoral inflammation, possibly contributing to neuroprotection, whereas neutralization of FasL and TNF had no effect. In future studies, the lpr mouse strain may be utilized as a model to further characterize molecular and cellular mechanisms protecting against secondary brain damage after TBI.

The naturally processed CD95L elicits a c-yes/calcium/PI3K-driven cell migration pathway

Patients affected by chronic inflammatory disorders display high amounts of soluble CD95L. This homotrimeric ligand arises from the cleavage by metalloproteases of its membrane-bound counterpart, a strong apoptotic inducer. In contrast, the naturally processed CD95L is viewed as an apoptotic antagonist competing with its membrane counterpart for binding to CD95. Recent reports pinpointed that activation of CD95 may attract myeloid and tumoral cells, which display resistance to the CD95-mediated apoptotic signal. However, all these studies were performed using chimeric CD95Ls (oligomerized forms), which behave as the membrane-bound ligand and not as the naturally processed CD95L. Herein, we examine the biological effects of the metalloprotease-cleaved CD95L on CD95-sensitive activated T-lymphocytes. We demonstrate that cleaved CD95L (cl-CD95L), found increased in sera of systemic lupus erythematosus (SLE) patients as compared to that of healthy individuals, promotes the formation of migrating pseudopods at the leading edge of which the death receptor CD95 is capped (confocal microscopy). Using different migration assays (wound healing/Boyden Chamber/endothelial transmigration), we uncover that cl-CD95L promotes cell migration through a c-yes/Ca²⁺/PI3K-driven signaling pathway, which relies on the formation of a CD95-containing complex designated the MISC for Motility-Inducing Signaling Complex. These findings revisit the role of the metalloprotease-cleaved CD95L and emphasize that the increase in cl-CD95L observed in patients affected by chronic inflammatory disorders may fuel the local or systemic tissue damage by promoting tissue-filtration of immune cells.

Repertoire of microglial and macrophage responses after spinal cord injury

Macrophages from the peripheral circulation and those derived from resident microglia are among the main effector cells of the inflammatory response that follows spinal cord trauma. There has been considerable debate in the field as to whether the inflammatory response is good or bad for tissue protection and repair. Recent studies on macrophage polarization in non-neural tissues have shed much light on their changing functional states. In the context of this literature, we discuss the activation of macrophages and microglia following spinal cord injury, and their effects on repair. Harnessing their anti-inflammatory properties could pave the way for new therapeutic strategies for spinal cord trauma.

Human neuropathological and animal model evidence supporting a role for Fas-mediated apoptosis and inflammation in cervical spondylotic myelopathy

Although cervical spondylotic myelopathy is a common cause of chronic spinal cord dysfunction in humans, little is known about the molecular mechanisms underlying the progressive neural degeneration characterized by this condition. Based on animal models of cervical spondylotic myelopathy and traumatic spinal cord injury, we hypothesized that Fas-mediated apoptosis and inflammation may play an important role in the pathobiology of human cervical spondylotic myelopathy. We further hypothesized that neutralization of the Fas ligand using a function-blocking antibody would reduce cell death, attenuate inflammation, promote axonal repair and enhance functional neurological outcomes in animal models of cervical spondylotic myelopathy. We examined molecular changes in post-mortem human spinal cord tissue from eight patients with cervical spondylotic myelopathy and four control cases. Complementary studies were conducted using a mouse model of cervical spondylotic myelopathy (twy/twy mice that develop spontaneous cord compression at C2-C3). We observed Fas-mediated apoptosis of neurons and oligodendrocytes and an increase in inflammatory cells in the compressed spinal cords of patients with cervical spondylotic myelopathy. Furthermore, neutralization of Fas ligand with a function-blocking antibody in twy/twy mice reduced neural inflammation at the lesion mediated by macrophages and activated microglia, glial scar formation and caspase-9 activation. It was also associated with increased expression of Bcl-2 and promoted dramatic functional neurological recovery. Our data demonstrate, for the first time in humans, the potential contribution of Fas-mediated cell death and inflammation to the pathobiology of cervical spondylotic myelopathy. Complementary data in a murine model of cervical spondylotic myelopathy further suggest that targeting the Fas death receptor pathway is a viable neuroprotective strategy to attenuate neural degeneration and optimize neurological recovery in cervical spondylotic myelopathy. Our findings highlight the possibility of medical treatments for cervical spondylotic myelopathy that are complementary to surgical decompression.

Emerging concepts in myeloid cell biology after spinal cord injury

Traumatic spinal cord injury (SCI) affects the activation, migration, and function of microglia, neutrophils and monocyte/macrophages. Because these myeloid cells can positively and negatively affect survival of neurons and glia, they are among the most commonly studied immune cells. However, the mechanisms that regulate myeloid cell activation and recruitment after SCI have not been adequately defined. In general, the dynamics and composition of myeloid cell recruitment to the injured spinal cord are consistent between mammalian species; only the onset, duration, and magnitude of the response vary. Emerging data, mostly from rat and mouse SCI models, indicate that resident and recruited myeloid cells are derived from multiple sources, including the yolk sac during development and the bone marrow and spleen in adulthood. After SCI, a complex array of chemokines and cytokines regulate myelopoiesis and intraspinal trafficking of myeloid cells. As these cells accumulate in the injured spinal cord, the collective actions of diverse cues in the lesion environment help to create an inflammatory response marked by tremendous phenotypic and functional heterogeneity. Indeed, it is difficult to attribute specific reparative or injurious functions to one or more myeloid cells because of convergence of cell function and difficulties in using specific molecular markers to distinguish between subsets of myeloid cell populations. Here we review each of these concepts and include a discussion of future challenges that will need to be overcome to develop newer and improved immune modulatory therapies for the injured brain or spinal cord.

Opposing roles for membrane bound and soluble Fas ligand in glaucoma-associated retinal ganglion cell death

Glaucoma, the most frequent optic neuropathy, is a leading cause of blindness worldwide. Death of retinal ganglion cells (RGCs) occurs in all forms of glaucoma and accounts for the loss of vision, however the molecular mechanisms that cause RGC loss remain unclear. The pro-apoptotic molecule, Fas ligand, is a transmembrane protein that can be cleaved from the cell surface by metalloproteinases to release a soluble protein with antagonistic activity. Previous studies documented that constitutive ocular expression of FasL maintained immune privilege and prevented neoangeogenesis. We now show that FasL also plays a major role in retinal neurotoxicity. Importantly, in both TNFα triggered RGC death and a spontaneous model of glaucoma, gene-targeted mice that express only full-length FasL exhibit accelerated RGC death. By contrast, FasL-deficiency, or administration of soluble FasL, protected RGCs from cell death. These data identify membrane-bound FasL as a critical effector molecule and potential therapeutic target in glaucoma.

Harnessing programmed cell death as a therapeutic strategy in rheumatic diseases

Programmed cell death (PCD) is a key process in the regulation of immune cell development and peripheral immune homeostasis. Caspase-dependent apoptosis, as well as a number of alternative cell death mechanisms, account for immune cell PCD induced by cell-intrinsic and extrinsic pathways. In animal models, compelling evidence has emerged that genetic defects in PCD can result in autoimmune disease. Autoimmune disease can arise from single-gene mutations that affect PCD, and defective PCD has been observed in some tissues and cells from patients with rheumatic disease. Selectively inducing PCD in autoreactive B and T cells is very attractive as a therapeutic strategy because it offers the possibility of permanent elimination of these pathogenic cell subsets. In addition, the anti-inflammatory effects of apoptotic cells may add to the therapeutic benefit of induced PCD. Immune cell subsets vary widely in their sensitivity to specific inducers of cell death, and understanding these differences is key to predicting the outcome of inducing apoptosis for therapeutic means. Here, we review approaches that have been used to induce PCD in the treatment of autoimmune disease, and describe the prospects of bringing these experimental strategies into clinical practice.

A deadly migration

CD95 has long been viewed as a death receptor regulating apoptosis. In this issue of Immunity, Letellier et al. (2010) tell us a different story, about the capability of CD95L to regulate leukocyte recruitment to sites of inflammation.

Inflammation dampened by gelatinase A cleavage of monocyte chemoattractant protein-3

Tissue degradation by the matrix metalloproteinase gelatinase A is pivotal to inflammation and metastases. Recognizing the catalytic importance of substrate-binding exosites outside the catalytic domain, we screened for extracellular substrates using the gelatinase A hemopexin domain as bait in the yeast two-hybrid system. Monocyte chemoattractant protein-3 (MCP-3) was identified as a physiological substrate of gelatinase A. Cleaved MCP-3 binds to CC-chemokine receptors-1, -2, and -3, but no longer induces calcium fluxes or promotes chemotaxis, and instead acts as a general chemokine antagonist that dampens inflammation. This suggests that matrix metalloproteinases are both effectors and regulators of the inflammatory response.