No abstract

In experimental autoimmune encephalomyelitis (EAE), intravenous transfer of activated CD4+ myelin-specific T cells is sufficient to induce disease. Transferred T cells access the CNS parenchyma by trafficking across the blood brain barrier (BBB) vascular endothelium into the perivascular space, and then across the glial limitans that is made up of astrocytes and microglia. Flow cytometry analysis of cells isolated from CNS tissue does not distinguish between T cell populations at the various stages of migration. In this study, we have used GK1.5 (anti-CD4) treatment along with immunohistochemistry to distinguish between populations of T cells that are associated with the vasculature, T cells that have migrated into the perivascular space, and T cells in the parenchyma. We have also re-evaluated antigen specificity requirements of T cells as they are recruited to the CNS parenchyma. Activated myelin-specific T cells are restricted to the CNS vasculature for at least 24 h post transfer. MHC class II expression on the recipient is required for cells to traffic across the CNS vascular endothelium. Further, Con A-stimulated or non-CNS-specific (ovalbumin-specific) T cells fail to migrate into the perivascular space, and only enter the CNS parenchyma when cotransferred with myelin-specific T cells. Our results indicate that Th1 populations cannot accumulate in the perivascular (subarachnoid, Virchow-Robbins) space without a CNS antigen-specific signal.

Experimental autoimmune encephalomyelitis (EAE) is an autoimmune demyelinating disease of the central nervous system (CNS). Because of similarities in clinical symptoms and CNS histology, 1-5 EAE serves as a model for multiple sclerosis and can be induced in mice by either immunization with myelin protein or peptides 6 or by adoptive transfer of myelin-specific Th1 CD4 ϩ T cells. 7,8As a result, inflammatory cells consisting mostly of CD4 ϩ T lymphocytes and macrophages infiltrate the CNS leading to demyelination and neuronal damage. 9Tumor necrosis factor receptor 1 (TNFR1), also known as the p55 kd TNF receptor, binds to two ligands, TNF and lymphotoxin-␣. 10 The dominant signaling pathway for TNFR1 promotes inflammation by up-regulating inflammatory cytokines, chemokines, and adhesion molecules 11-17 and also suppresses apoptosis by the induction of IAPs (inhibitors of apoptosis) through nuclear factor (NF)-B-dependent pathways.18 TNFR1 also has the ability to induce apoptosis through a death domain in its cytoplasmic region that initiates the FADD-dependent extrinsic apoptotic pathway. 19Our previous experiments have demonstrated that TNFR1 contributes to the pathogenesis of EAE mainly by promoting CNS inflammation, 20 and thereby, in the absence of TNFR1 expression, clinical disease is limited. Through our adoptive transfer experiments we have found a dramatic difference in the location of encephalitogenic T cells within the CNS of wild-type (WT) versus TNFR1-null mice. Although we observed equivalent numbers of T cells in the CNS of TNFR1-deficient mice compared to WT mice, we found that the T cells in the TNFR1-null animals were confined to the leptomeninges and perivascular spaces of the spinal cord, whereas in the