Effect of transforming growth factor-beta1 on microglial MHC-class II expression

Neuroprotective effects of G-CSF administration in microglia-mediated reactive T cell activation in vitro

G-CSF is a growth factor that has known neuroprotective effects in a variety of experimental brain injury models. As both antigen-presenting microglia and reactive T cells are key components in the development and progression of EAE, the aim of this study is to investigate the neuroprotective effects of recombinant human G-CSF, as administered in microglia-mediated reactive T cell assay in vitro. Our results indicate that G-CSF treatment has no apparent effect for the resting un-activated microglia. G-CSF pre-protection of microglia increased protective cytokine IL-4 production and effectively inhibited the productions of NO and other inflammatory mediators (IFN-γ, TNF-α, IL-1β, IL-17, and chemokine MCP-1) after LPS stimulation. G-CSF suppressed the proliferative response of microglia-mediated MOG_35-55 reactive T cells. G-CSF-microglia-T cells increased IL-4 and IL-10 secretions and decreased IFN-γ, TNF-α, and IL-17 productions. G-CSF significantly elevated CD4⁺CD25⁺ regulatory T cell subset in microglia-mediated reactive T cells. Moreover, G-CSF inhibited MHC-II expression of microglia after LPS activation or in the interactions of microglia and reactive T cells. G-CSF administration induced the apoptosis and enhanced the G0/G1 to S phase transition and elevated the gene expression of apoptosis markers in microglia-mediated reactive T cells after stimulated by specific antigen MOG_35-55. These findings reveal that G-CSF administration potently neuroprotects the central nervous system (CNS) from immune-mediated damage in microglia-mediated reactive T cell activation. Apoptosis of reactive T cells in CNS is important in attenuating the development of autoimmune CNS diseases. G-CSF administration has neuroprotective effects in CNS and the potential to be a therapeutic agent in multiple sclerosis.

STAT1-Independent Down-Regulation of Interferon-Gamma-Induced Class II Transactivator and HLA-DR Expression by Transforming Growth Factor Beta-1 in Human Glomerular Endothelial Cells

BACKGROUND

The competition between STAT1 and Smad3 for a limiting amount of the nuclear protein p300, a transcriptional coactivator, was suggested to be a mechanism for the antagonism between interferon-gamma (IFN-gamma) and transforming growth factor-beta1 (TGF-beta1). We investigated the effect of TGF-beta1 on IFN-gamma-induced HLA-DR production in cultured human glomerular endothelial cells (HGECs), and the involvement of p300 in this process.

METHODS

Cell surface expression of HLA-DR and mRNA levels of HLA-DR and class II transactivator (CIITA), the master regulator of HLA-DR gene transcription, were measured by cellular ELISA and Northern blot, respectively. The levels of STAT1 and Smad3 protein were analyzed by Western blot. Nuclear binding activity of STAT1 was assessed by electrophoretic mobility shift assay.

RESULTS

IFN-gamma increased the cell surface expression of HLA-DR along with increases in the mRNA levels of CIITA and HLA-DR, while these stimulatory effects of IFN-gamma were down-regulated by TGF-beta1. IFN-gamma increased phosphorylation of STAT1 and this activation was not inhibited by TGF-beta1. IFN-gamma increased binding of p-STAT1 to p300, while TGF-beta1 increased binding of Smad3 to p300. TGF-beta1-induced Smad3 binding to p300 was inhibited by IFN-gamma, whereas IFN-gamma-induced p-STAT1 binding to p300 was not inhibited by TGF-beta1. IFN-gamma increased DNA binding activity of STAT1. Inhibition of interaction between STAT1 and p300 by addition of anti-p300 antibody to nuclear extract down-regulated DNA binding activity of STAT1. In contrast, TGF-beta1 did not inhibit IFN-gamma-induced STAT1 binding to DNA.

CONCLUSIONS

TGF-beta1 down-regulated IFN-gamma-induced CIITA and HLA-DR expression in HGECs. Though there was an antagonism between IFN-gamma and TGF-beta1, the competition for p300 between p-STAT1 and Smad3 was not the mechanism for it.

A DNA vaccine expressing tyrosinase-related protein-2 induces T-cell-mediated protection against mouse glioblastoma

A mouse glioblastoma cell line, termed GL261, was shown to express high levels of proteins involved in melanin biosynthesis such as the tyrosinase-related protein-2 (TRP-2), which is commonly overexpressed in melanoma cells. Mice injected with GL261 cells developed a CD8(+) T-cell response to TRP-2 and a DNA vaccine expressing human (h)TRP-2 induced CD8(+) T cells that recognized TRP-2 expressed by GL261 cells indicating that this melanoma-associated antigen may be suited for active immunotherapy of glioblastoma. Mice vaccinated with a DNA vaccine expressing TRP-2 were partially protected against subcutaneous, intravenous, or intracerebral challenge with the glioblastoma cells. Vaccine-induced protection against intracerebral challenge required both CD4(+) and CD8(+) T cells. Vaccine efficacy was enhanced upon addition of IL-12 as a genetic adjuvant. These results indicate that this well-defined melanoma-associated antigen can induce an adaptive immune response, which limits the intracerebral progression of a glioblastoma.

Lipopolysaccharide/interferon-gamma and not transforming growth factor beta inhibits retinal microglial migration from retinal explant

BACKGROUND

/aims: The retina possesses a rich network of CD45(+) positive myeloid derived cells that both surround inner retinal vessels and lie within the retina (microglia). Microglia migrate and accumulate in response to neurodegeneration and inflammation. Although microglia express MHC class II, their role remains undefined. The aims of this study are to investigate changes in human microglia phenotype, migration, and activation status in response to pro-inflammatory and anti-inflammatory stimulation.

METHODS

Donor eyes were obtained from the Bristol Eye Bank with consent and whole retina was removed. 5 mm retinal trephines were cultured in glucose enhanced RPMI on cell culture insert membranes for up to 72 hours. The effects of lipopolysaccharide/interferon-gamma (LPS/IFNgamma) and transforming growth factor beta inhibits (TGFbeta) stimulation, alone or in combination, on migration, phenotype, and activation status (iNOS expression) of microglia were studied using immunofluorescence and cytokine analysis by ELISA.

RESULTS

CD45(+) MHC class II(+) retinal microglia were observed within retinal explants, and in culture microglia readily migrated, adhered to culture membrane, downregulated MHC class II expression, and produced interleukin 12 (IL-12) and tumour necrosis factor alpha (TNFalpha). Following LPS/IFNgamma stimulation microglia remained MHC class II(-) iNOS(-), and secreted IL-10. Migration was suppressed and this could be reversed by neutralising IL-10 activity. TGFbeta did not affect ability of microglia to migrate and was unable to reverse LPS/IFNgamma induced suppression.

CONCLUSIONS

Microglia readily migrate from retinal explants and are subsequently MHC class II(-), iNOS(-), and generate IL-12. In response to LPS/IFNgamma microglia produce IL-10, which inhibits both their migration and activation. TGFbeta was unable to counter LPS/IFNgamma effects. The data infer that microglia respond coordinately, dependent upon initial cytokine stimulation, but paradoxically respond to classic myeloid activation signals.

Microglia in neurodegeneration: molecular aspects

Inflammatory events in the CNS are associated with injuries as well as with well-known chronic degenerative diseases, such as Multiple Sclerosis, Parkinson's, or Alzheimer's disease. Compared to inflammation in peripheral tissues, inflammation in brain appears to follow distinct pathways and time-courses, which likely has to do with a relatively strong immunosuppression in that organ. For this reason, it is of great importance to get insights into the molecular mechanism governing immune reactions in brain tissue. This task is hard to achieve in vivo, but can be approached by studying the major cell type responsible for brain inflammation, the microglia, in culture. Since these cells are the only professional antigen-presenting cells resident in brain parenchyma, molecular mechanisms of antigen presentation are being discussed first. After covering the expression and regulation of anti- and proinflammatory cytokines, induction and regulation of two key enzymes and their products-COX-2 and iNOS-are summarized. Possibly, pivotal molecular targets for drug therapies of brain disorders will be discovered in intracellular signaling pathways leading to activation of transcription factors. Finally, the impact of growth factors, of neurotrophins in particular, is highlighted. It is concluded that the presently available data on the molecular level is far from being statisfying, but that only from better insights into molecular events will we obtain the information required for more specific therapies.