Heterogeneity of mouse brain macrophages in alloantigen presentation to naive CD8+ T cells as revealed by a panel of microglial cell lines

Identification of new CNS-resident macrophage subpopulation molecular markers for the discrimination with murine systemic macrophages

A controversial issue in neurobiology concerns the respective functions of central nervous system (CNS)-resident macrophages and systemic infiltrating macrophages morphologically and phenotypically similar during most of CNS injury processes. In a previous work, we isolated sixteen mRNAs differentially expressed between two microglial EOC clones. By studying their pattern of expression, we found that three of them were not expressed in peripheral macrophages, even after stimulation with IFNgamma, TNFalpha or IL10. These three molecules are physiologically expressed by murine adult microglia and could be used to evaluate in vivo their discriminative potential toward CNS-infiltrating macrophages during inflammatory events.

Vitamin D3 inhibits proinflammatory cytokines and nitric oxide production by the EOC13 microglial cell line

In recent years, a neuroimmunomodulatory role for 1,25-dihydroxyvitamine D(3) [1,25(OH)(2)D(3)] has emerged. Microglial cells present a potential target for the effects of this hormone in the brain. This study focuses on the effect of 1,25(OH)(2)D(3) on the expression and production of inflammatory cytokines and nitric oxide (NO) by the EOC13 microglial cell line. The presence of the vitamin D3 receptor in microglia was demonstrated by RT-PCR. 1,25(OH)(2)D(3) inhibited the production of tumor necrosis factor-alpha, interleukin-6, and NO by stimulated microglia in a concentration-related fashion. The production of transforming growth factor-beta1 (TGF-beta1), an anti-inflammatory cytokine, was not modified in the presence of 1,25(OH)(2)D(3), indicating that the effects of 1,25(OH)(2)D(3) may not involve TGF-beta1 regulation. These results show that 1,25(OH)(2)D(3) has direct anti-inflammatory properties on microglia. It further supports the hypothesis that 1,25(OH)(2)D(3) could be involved in the maintenance of the brain homeostasis and may have a therapeutic potential in inflammatory pathologies of the central nervous system.

Identification and IFNgamma-regulation of differentially expressed mRNAs in murine microglial and CNS-associated macrophage subpopulations

CNS-resident macrophages (microglia and CNS-associated macrophages) are the main immunocompetent cells of the central nervous system (CNS) and respond by rapid activation to brain injury. Molecular events occurring during IFNgamma-activation and identification of potential markers of the CNS-resident macrophage subsets were investigated using microglial-derived clones (EOC) differing in their morphology and their antigen presenting activities for CD4+ and CD8+ T-cells. By applying the subtractive process of cDNA representational difference analysis (cRDA), 16 differentially expressed mRNAs were isolated and sequenced, revealing 8 known and 8 novel molecules; 15 of these messages were unpreviously reported in microglia. Two markers of all activated microglial EOC cells were identified (iNOS; IRG-1) and specific subpopulation markers were highlighted, including molecules known to be closely expressed in perivascular spaces. Moreover, some messages could support the distinct morphology, adhesive characteristics, and potential functions of the different clones.

Microglia exhibit clonal variability in eliciting cytotoxic T lymphocyte responses independent of class I expression

Microglia are important immunoregulatory cells within the central nervous system (CNS). Viral infection of primary microglia and splenic macrophage clones revealed that both exhibited a heterogeneous, but relatively low, sensitivity to cytolysis mediated by CD8(+) cytotoxic T lymphocytes (CTL). The majority of clones were poor in processing and presenting epitopes, despite triggering lysis when coated with peptide. These characteristics were retained by stable microglia lines. Reduced lysis did not correlate with class I expression and IFN-gamma treatment only partially enhanced recognition. In contrast, targeting the epitope into the endoplasmic reticulum restored cytolysis to levels achieved with exogenous peptide. An inherent resistance to cytolysis was revealed by efficient engagement of T cells in competition assays and the inability of saturating peptide to enhance cytolysis. These data suggest that microglia heterogeneity in antigen processing, in addition to low sensitivity to CTL lysis, contributes to limited CD8(+) T cell responses and viral CNS persistence.