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 alpha-1-antitrypsin (alpha 1), 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.