Investigation of in vivo activated T cells in multiple sclerosis and inflammatory central nervous system diseases.

Monoclonal antibodies have recently been characterized which identify activated T cells at different stages of differentiation. We compared the expression of the late appearing activation antigen defined by monoclonal antibody TS2/7 with the expression of early appearing activation antigens in a group of patients with active multiple sclerosis, encephalitis, non-inflammatory other neurologic diseases, and normal controls. An increase in TS2/7 reactivity of peripheral blood T cells was found in MS patients compared to controls (P less than 0.001), however, there was no increase in the level of early activation antigens. This was in contrast to three patients with viral encephalitis, who had an increase in the early activation antigen 4F2, but minimal, if any, increase in the TS2/7 reactive antigen. This study demonstrates that in vivo, as in vitro, it is possible to identify multiple differentiation stages for activated T cells. Furthermore, the presence of activated T cells in the peripheral blood of multiple sclerosis patients suggests that there is systemic immune activation in MS, and could provide a means to monitor abnormal immunologic activity in MS when these cells are functionally characterized.