Reactive gliosis is a characteristic response of astrocytes to inflammation and trauma of the central nervous system. To investigate whether soluble factors (cytokines) from inflammatory mononuclear cells that accumulate at lesion sites can provide the cellular signals to initiate gliosis and to identify such cytokines, we have tested and found that supernatants derived from subsets of activated human T lymphocytes (CD8' or CD41) are potent mitogens for cultured human adult astrocytes. This effect is blocked by a neutralizing antibody to -interferon (IFN). Recombinant A consideration in relating relevance of in vitro proliferation results to reactive gliosis in vivo is that gliotic scars seldom develop after insults to the embryonic brain (22-24) but are common features in adult brain injuries. Thus, it becomes important to assess proliferation of astrocytes derived from adult animals, rather than from neonatal ones. We have adopted such a strategy by using adult human astrocytes isolated from surgical brain biopsies and have addressed the following questions. Do activated human T lymphocytes produce sufficient cytokines to induce proliferation of cultured adult human astrocytes; if so, which cytokine (s) (see Results), were treated with trysin and seeded on poly(L-lysine)-coated (10 jag/ml) 9-mm Aclar fluorocarbon coverslips at 10,000 cells per coverslip. These mixed cells were used for the present study; methods for eliminating microglia from rodent glia cultures (leucine methyl ester and silica ingestion) (28-30) were not effective for human preparations. Culture medium was Eagle's minimum essential medium supplemented with 5% (vol/vol) fetal calf serum, Gentamicin (20 gg/ml), and dextrose (1 mg/ml) (all from GIBCO).

Expression of Class II major histocompatibility complex (MHC) antigens on astrocytes has been implicated as contributing to the immune responses characteristic of chronic autoimmune diseases of the central nervous system. We examined the properties and regulation of HLA-DR on cultured human adult astrocytes. We found that a proportion of human astrocytes from each of fifteen individual donors expressed HLA-DR under basal culture condition; while this proportion differed among the human subjects (range 3-65%), the results for each individual remained relatively constant when analyzed at several time points (up to 125 days in vitro). Attempts to modulate HLA-DR expression by a variety of cytokines likely to be present in inflammatory infiltrates in the brain showed that only gamma-interferon could increase the proportion of human astrocytes that expressed HLA-DR. Whether the variability of HLA-DR expression on astrocytes between different individuals reflects a genetic trait which can influence susceptibility to autoimmune central nervous system diseases remains to be determined.

The efficacy of glatiramer acetate in multiple sclerosis (MS) is thought to involve the production of Th2 regulatory lymphocytes that secrete anti-inflammatory cytokines; however, other mechanisms cannot be excluded Given that activated T lymphocytes infiltrate into the CNS and become in dose proximity to microglia, we evaluated whether glatiramer acetate affects the potential interaction between T cells and microglia. We report that the co-culture of activated T lymphocytes with microglia led to the induction of several cytokines, and that these were reduced by glatiramer acetate treatment Morphological transformation of bipolar/ramified microglia into an activated ameboid form was attenuated by glatiramer acetate. These results reveal a novel mechanism for glatiramer acetate: the impairment of activated T cells to effectively interact with microglia to produce cytokines. The net result of a non-inflammatory milieu within the CNS, in spite of T cell infiltration, may help account for the amelioration of disease activity in MS patients on glatiramer acetate therapy.

Human adult astrocytes derived from brain surgical resections showed marked morphologic heterogeneity when cultured in vitro, ranging from a flat, fibroblast-like appearance to process-bearing cells with little soma cytoplasm. The majority of cells were intermediate in morphology, bearing a prominent cytoplasmic cell body with processes radiating from them. The morphologic heterogeneity was more extensive than that of adult rat astrocytes, and was not correlated with the extent of attendant gliosis in the surgical specimens, or the site of the surgical resection. None of the human astrocytes expressed A2B5, thus preventing their classification on basis of lineage into type 1 or type 2 astrocytes. However, functional differences appear to exist between subpopulations of human astrocytes, since the proportion of process-bearing human astrocytes that expressed HLA-DR in vitro was significantly greater than that found for flat astrocytes.

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