Ia expression in chronic relapsing experimental allergic encephalomyelitis induced by long-term cultured T cell lines in mice.

Chronic relapsing experimental allergic encephalomyelitis was induced in SJL mice by adoptive transfer of long-term cultured T cell lines. The T cells which were activated with myelin basic protein (MBP) derived from various species, all induced chronic relapsing experimental allergic encephalomyelitis with a similar high incidence. During the relapsing stage, lymphocytes obtained from the spleen responded well to MBP and were capable of transferring experimental allergic encephalomyelitis, whereas thymus lymphocytes did not respond to MBP. There was no difference in the proliferative response of splenocytes to MBP when splenocytes were isolated either from mice with clinical relapse or from mice that did not relapse. Pathological examination revealed a transient appearance of inflammatory cells during the acute stage. Similar cell infiltrates were also observed at the relapsing stage. The I-region associated (Ia) antigens appeared on vessels and astrocytes in the acute inflammatory lesions which coincided with the appearance of inflammatory cell infiltrates. Ia antigen expression diminished with the disappearance of inflammatory cells. During the relapsing stage, the Ia antigens were also expressed on the vessels and astrocytes in the fresh lesions. Our data indicate that MBP-reactive T cells persist at least in the spleen, for a long time. They may be reactivated by certain mechanisms probably in the central nervous system associated with the Ia-antigen expression, which facilitates the effector phase again. The initial event that triggers the Ia-expression is not known as yet.