Targeting Astrocytes Research Articles

Target APC polarization at immunological synapses (IS) in vivo: infected astrocytes polarize towards CTL cells during the brain antiviral immune response. (91.13)

Abstract IS mediate intercellular communication between T cells and APCs. T cells’ structure and membrane proteins are polarized at IS. T cell polarization at the IS consists of a peripheral supramolecular activation cluster (pSMAC), which is high in LFA-1, and low in TCR, and a central SMAC, high in TCR, and low in LFA-1. The MTOC, Golgi and secretory vesicles are also polarized towards the IS. Here we demonstrate that during an anti-viral immune response in the brain, APCs are also polarized. Brain astrocytes were infected with an adenoviral (Ad) vector expressing Thymidine Kinase (TK), a marker of infected cells. 30 days later we immunized systemically against Ads, and 14 days later animals were sacrificed and brains prepared for microscopical analysis. Brain sections were immunostained for TCR, LFA-1, TK, EAAT2, γ-Tubulin, α-Tubulin and GM130. Confocal analysis revealed that target infected astrocytes, normally a non-polarized cell, became completely repolarized. Target astrocytes retract all processes and form a single large protrusion towards the T cell. The MTOC and Golgi are then targeted towards and into the protrusion, and membrane proteins become polarized. These results demonstrate that CTL signaling, potentially mediated through IS, induces profound morphological changes in target APCs. This work was funded by grants from NINDS/NIH.

Delineation of tissue damage mechanisms in experimental autoimmune encephalomyelitis (EAE). II. Characteristics of astrocyte detachment mediated by myelin basic protein (MBP) specific CD4 + T lymphocytes

We have shown that encephalitogenic, myelin basic protein (MBP)-specific CD4 + T cells can cause astrocyte and oligodendrocyte detachment in vitro. Similar processes may damage the central nervous system (CNS) in vivo by causing disorganization and destruction of brain tissue structure. The finding that ‘bystander’ allogeneic fibrosarcoma cells were detached by MBP-specific CD4 + T cells only when syngeneic astrocytes were present, suggested that a soluble cell-detaching factor (CDF) is released during the specific astrocyte-CD4 + effector interaction. In this study, CDF activity was detected in the supernatants of MBP-reactive CD4 + T cells incubated with concanavalin A or astrocytes. Lymphocyte-induced astrocyte lysis, but not detachment, was inhibited by the protein synthesis inhibitors, cycloheximide and puromycin, indicating that de novo protein synthesis is required for this type of lysis, but not for detachment. Astrocyte detachment was not inhibited, but rather augmented, by the trypsin inhibitors, soybean trypsin inhibitor (SBTI) and α-1-antitrypsin (α1), suggesting that the CDF activity is not due to tryptic serine proteases, although it may be protease susceptible. The heparanase inhibitor, heparin, inhibited CD4 + T cell-mediated astrocyte detachment at low doses, but augmented detachment at higher doses, indicating that detaching activity is not due to heparanases. The actin microfilament disrupting agent, cytochalasin B (CB), inhibited astrocyte detachment induced by MBP-specific CD4 + T cells. CB pretreatment of the target astrocytes, but not of the effector CD4 + T cells, inhibited astrocyte detachment, suggesting that the integrity of the target's, but not the effector's, cytoskeleton is required for astrocyte detachment. The results herein suggest that during astrocyte interaction with MBP-specific CD4 + T cells, soluble factors are released that trigger an intrinsic astrocyte detachment mechanism.

Brain inflammatory exudate in Junin virus-infected rats: Its characterization by the immunoperoxidase (PAP) technique

Morphologic changes in cyclophosphamide (CY)-suppressed vs. control non-suppressed new-born rats infected i.c. with XJC13 strain of Junin virus were compared and the cells involved in CNS lesions were identified by the PAP technique. Fifty per cent of the control rats exhibited widespread cerebral necrosis vs. only 15% of the immunosuppressed animals. The first cells to reach Junin virus-infected CNS in controls were T lymphocytes, which destroyed viral antigen-laden target neurons and astrocytes. B lymphocytes and macrophages, presumably attracted by viral antigen and/or by lymphokines, made their appearance a day or two later. Activated macrophages phagocytosed necrotic cells and perhaps exerted a cytotoxic effect upon target neural cells, whereas the actual role of B lymphocytes requires further explanation. In CY-treated rats, cerebral lesions were smaller and the cellular exudate, though similar, proved much scantier than in controls. A similar extent of cerebellar necrosis was observed in both groups.