Journal of Neuroimmunology, 70 (2) 1996, pp 93-101. http://www.sciencedirect.com/science/journal/01655728 http://dx.doi.org/10.1016/S0165-5728%2896%2900043-4 Corticosteroid Treatment Of Experimental Autoimmune Encephalomyelitis In The Lewis Rat Results in Loss of Vβ 8.2 + And Myelin Basic Protein-Reactive Cells from the Spinal Cord, with Increased Total T-Cell Apoptosis but Reduced Apoptosis of Vβ 8.2 + Cells P. A. McCombe, I. Nickson, Z. Tabi and M. P. Pender Neuroimmunology Research Unit, Department of Medicine, The University of Queensland, Clinical Sciences Building, Royal Brisbane Hospital, Herston, Qld. 4029, Australia Abstract We have studied the effects of corticosteroid treatment on the numbers of lymphocytes obtained from the spinal cords of Lewis rats with acute experimental autoimmune encephalomyelitis (EAE) induced by inoculation with myelin basic protein (MBP) and adjuvants. Flow cytometric studies showed that treatment with dexamethasone (4 mg/kg) 8–12 h prior to study on day 14 after inoculation resulted in a reduction in the numbers of CD5 + , TCR + and V 8.2 + cells in the spinal cord. Limiting dilution analysis indicated that dexamethasone treatment 12 h prior to study on day 12 after inoculation reduced the frequencies of MBP-reactive and interleukin-2-responsive lymphocytes in the spinal cord to low levels, but reduced the frequency of concanavalin-A-responsive lymphocytes to a lesser extent. Using propidium iodide staining of nuclear chromatin we also studied lymphocyte apoptosis. Greater numbers of apoptotic cells were found in the cells extracted from the spinal cords of rats, examined on day 14, that had been treated 1–12 h previously with dexamethasone, than in saline-treated controls. This increased level of apoptosis was observed in the CD5 + and TCR + cell populations. At 1–4 h after dexamethasone treatment there was a reduction in the selective apoptosis of V 8.2 + cells that normally occurs during spontaneous recovery from EAE. Therefore apoptosis of V 8.2 + cells cannot explain the reduction in the numbers of V 8.2 + cells and MBP-reactive cells in the CNS after dexamethasone treatment. By 8–12 h after dexamethasone treatment the selectivity of the apoptotic process was restored. These studies suggest that a reduction in the number of T-lymphocytes in the central nervous system contributes to the beneficial effects of corticosteroids in EAE. Keywords: apoptosis; corticosteroids; experimental autoimmune encephalomyelitis; multiple sclerosis; recovery; T-lymphocytes 1. Introduction Experimental autoimmune encephalomyelitis (EAE) is mediated by CD4 + T-lymphocytes and can be induced in susceptible animals by active inoculation with myelin antigens and adjuvants or by the passive transfer of T-lymphocytes sensitized to these antigens. EAE is the best available animal model of multiple sclerosis. Recovery from EAE is associated with loss of T-lymphocytes from the central nervous system (CNS) (Matsumoto and Fujiwara, 1987; McCombe et al., 1992; Zeine and Owens, 1993) and apoptosis of these lymphocytes in the CNS (Pender et al., 1991 and Pender et al., 1992; Schmied et al., 1993). In the Lewis rat, the encephalitogenic lymphocytes in EAE induced by inoculation with myelin basic protein (MBP) (MBP–EAE) are predominantly V 8.2 + (Offner et al., 1993; Tsuchida et al., 1993; Imrich et al., 1995). In MBP–EAE induced by the passive transfer of V 8.2 + MBP-specific