Experimental autoimmune myositis in the Lewis rat: lack of spontaneous T-cell apoptosis and therapeutic response to glucocorticosteroid application

Recently, it has been shown that inflammatory T-cells in human idiopathic m yositis only very rarely undergo spontaneous apoptosis. The animal model of experimental autoimmune myositis (EAM) in the Lewis rat was chosen to inve stigate whether similar findings hold true in rat muscle and if glucocortic osteroids act by induction of T-cell apoptosis in inflammatory lesions. The rate of spontaneous T-cell apoptosis in rat EAM was low, even in muscle sp ecimens with extensive inflammation. After intravenous glucocorticosteroid pulse therapy we found a dramatic increase in the rate of apoptotic T-cells in the inflamed muscles. Up to 50% of these apoptotic T-cells were CD8 pos itive apoptotic T-cells. T-cell apoptosis was significantly lower in simila rly inflamed muscle specimens of the control group. We suggest that glucoco rticosteroids induce apoptosis of endomysial T-cells in human idiopathic po lymyositis. Glucocorticosteroid-induced apoptosis may be a candidate mechan ism in the termination of inflammatory activity. (C) 2000 Elsevier Science B.V. All rights reserved.