EFFECT OF THEILER MURINE ENCEPHALOMYELITIS VIRUS AND CYTOKINES ON CULTURED OLIGODENDROCYTES AND ASTROCYTES

The pathogenesis of Theiler's murine encephalomyelitis virus (TMEV)-in duced demyelinating disease is still controversial. Our hypothesis is that primary infection of oligodendrocytes (OLGs) is not a crucial eve nt in the pathogenesis of demyelination in this model. In fact, it has been proposed that myelin may be destroyed, as an innocent bystander, following an antiviral delayed-type hypersensitivity (DTH) response. This hypothesis would not need widespread oligodendroglial infection, because virus present in other cells would be sufficient to trigger a DTH response, The present study demonstrates that cultured OLGs and as trocytes from susceptible strains of mice (SJL and DBA) and immortaliz ed OLGs can be infected with TMEV in vitro. Infection of OLGs, however , is at very low levels and does not result in overt cytolytic effect. In contrast, infection of immortalized OLGs is very efficient and res ults in clear cytolysis. Because an Important characteristic of DTH re sponses is the liberation of potentially injurious cytokines into adja cent tissues, we also examined the effects of mouse recombinant tumor necrosis factor-alpha (TNF-alpha), interleukin-1 alpha (IL-1 alpha), a nd interferon-gamma (IFN-gamma) on cultured OLGs and immortalized OLGs . We found that TNF-alpha caused immortalized OLG cytotoxicity in a ti me- and dose-dependent manner, In contrast, no cytotoxicity was observ ed on primary OLGs with any of the above cytokines. To determine wheth er functional effects could be demonstrated on primary OLGs by either virus or cytokines, we measured mRNA expression of different myelin pr oteins in primary and immortalized OLGs exposed to virus or TNF-alpha. Neither the BeAn strain or the GDVII strain of TMEV interfered with m yelin protein mRNA expression in primary OLGs, whereas GDVII virus dra matically reduced myelin OLG glycoprotein (MOG) mRNA in immortalized O LGs. Interestingly, although even high concentrations of TNF-alpha (10 ,000 U/ml) did not produce primary OLG cytotoxicity, they resulted in a significant reduction in mRNA for both myelin basic protein (MBP) an d MOG in these cells. TNF-alpha (at 500 U/ml) also specifically reduce d MOG mRNA in immortalized OLGs. Because immortalized OLGs are conside red to be arrested at an early stage of maturation, our results sugges t that immature OLGs are susceptible to both virus- and cytokine-depen dent cytotoxicity, whereas mature OLGs are resistant to cytolysis by e ither TMEV or cytokines. TNF-alpha, however, is capable of reducing mR NA expression of myelin proteins in primary OLGs; therefore, it may pa rticipate in the induction of demyelination, as suggested by the DTH-m ediated hypothesis. (C) 1996 Wiley-Liss, Inc.