Characteristics of in vitro cytotoxic effects of myelin basic protein-reactive T cell lines on syngeneic oligodendrocytes.

We have previously found that Lewis rat myelin basic protein (MBP)-reactive lymphocytes (Lc) were cytotoxic in vitro to cultured syngeneic oligodendrocytes (oligos). We report here additional studies to characterize this reaction. The effector lymphocytes in the cytotoxic reaction are also encephalitogenic as evidenced by the capacity of other aliquots of these cells to transfer experimental allergic encephalomyelitis (EAE). We confirmed that the presence of both MBP and antigen-presenting cells (APC) are required for this in vitro cytotoxic effect. This reaction (measured by 51Cr release from labeled oligos) is dose-dependent on the effector/target ratio with marked 51Cr release at a 20/l ratio. Effector/target cell contact is required since: (a) 51Cr release is not significantly increased when effector Lc and oligo are separated by a micropore membrane (28% vs. 24% spontaneous release); (b) no cytotoxic activity is present in the supernatant fluid of a toxic reaction. The adhesion of 51Cr-labeled effector Lc to unlabeled oligo is increased in the presence of both MBP and APC (21 +/- 1.0% of cell adhering) as compared with effector Lc + APC (12 +/- 2.7%), or effector Lc alone (14 +/- 2.8%). Surface expression of class I major histocompatibility complex (MHC) antigens was expressed on the surface of the target oligos during this in vitro cytotoxic reaction. This may explain our previously observed MHC restriction in this reaction. The findings described here may explain some of the in vivo pathogenic events in EAE.