Figure 4Cross-reactivity of GA-reactive T-cell lines is increased after daily injections of GA. Percentages of the GA-induced T-cell lines cross-reacting to each APL tested at each time point are shown for the 7 patients encoded by gray scale. Proliferative IFN-γ and IL-5 responses were examined for all T-cell lines and are represented separately in the top, middle, and lower third. A minimum SI of 2 and a difference of 2 SD over the background was required for classification as a cross-reactive T-cell line.

Infection of the central nervous (CNS) system by the human immunodeficiency virus (HIV) depends on the migration of infected hematogenous cells into the brain. We thus used quantitative light and electron microscopic immunocytochemistry to study the homing and turnover of bone marrow derived cells in the CNS in radiation bone marrow chimeras under normal conditions and in experimental autoimmune encephalomyelitis (EAE) as an experimental model of brain inflammation. Our studies suggest the following conclusions. First, the central nervous system is continuously patrolled by a small number of T-lymphocytes and monocytes. Meningeal and perivascular monocytes are slowly replaced by hematogenous cells under normal conditions, and this turnover is accelerated in the course of inflammation. In contrast, resident microglia represent a very stable cell pool, which in adult animals is only exceptionally replaced by hematogenous cells, even after recovery from severe brain inflammation. Second, although in bone-marrow-chimeric animals resident microglia, astrocytes, and ependymal cells are not able to present antigen to Lewis T-lymphocytes, the inflammatory reaction in EAE is qualitatively and quantitatively similar in these animals compared to fully histocompatible Lewis rats. Finally, resident microglia express the macrophage activation antigen ED1. Thus, microglia cells appear to function as effector cells in EAE lesions.

Since DNA fragmentation is a key feature of programmed cell death (PCD) and also occurs in certain stages of necrosis, we have adapted the methodology of in situ nicktranslation (IS") to detect DNA fragmentation on a singlecell level. We first established the technique for cell prepa-

The neuropathology of demyelinating lesions in multiple sclerosis was studied in specimens obtained by diagnostic needle biopsy during early stages of the disease. The lesions were characterized by a chronic inflammatory reaction dominated by lymphocytes and macrophages, plaque-like demyelination, and astroglial sclerosis. Oligodendrocytes within the lesions were studied by immunocytochemistry using antibodies against various myelin and oligodendroglia components. The expression of messenger RNA for proteolipid protein was determined by in situ hybridization. Our studies revealed that myelin-oligodendrocyte glycoprotein is a sensitive and reliable marker for identification of oligodendrocytes in demyelinated plaques. The results suggest that in the early course of the disease in some patients, oligodendrocytes may largely be preserved, whereas in others oligodendroglial loss is pronounced. Loss of oligodendrocytes was only marginally related to the stage of demyelinating activity within the lesions. These findings indicate that the pathogenesis of demyelination may vary within different multiple sclerosis patients.

Experimental autoimmune encephalomyelitis (EAE) was induced in Lewis rats by active immunization with myelin from guinea pig spinal cord by the encephalitogenic myelin basic protein or by adoptive transfer using myelin basic protein-specific CD4-positive T cells. Treatment with purified monoclonal antibody (1A-29) to the intercellular adhesion molecule-1 and its F(ab')2 fragments efficiently suppressed active EAE. Control treatment with an irrelevant antibody or saline did not alter the course of the disease. Histological sections of the central nervous system showed a pronounced reduction of inflammatory infiltrates during treatment with antibody to intercellular adhesion molecule-1. In the adoptive transfer model of EAE, 1A-29 had only a minor effect. Proliferation assays on lymph node cells ex vivo from 1A-29- and saline-treated animals were performed. Administration of 1A-29 suppressed antigen-specific T-cell proliferation. The differential effects in EAE versus adoptive transfer EAE suggest that 1A-29 acts predominantly on the induction phase of the immune response and, to a lesser extent, on the transendothelial migration of T cells. We conclude that intercellular adhesion molecule-1-dependent pathways are critically involved in the pathogenesis of EAE and that antibodies to leukocyte adhesion molecules could be a novel therapeutic approach to autoimmune disease of the central nervous system.