Severe perturbations of the blood T cell repertoire in polymyositis, but not dermatomyositis patients

Polymyositis and dermatomyositis are diseases characterized by muscle weakn ess and muscle inflammatory infiltrates. Their pathogenesis remains unclear . A central role for endomysial autoaggressive CD8(+) T cells is suspected in polymyositis and for perivascular B cells in dermatomyositis. We compare d the T cell repertoire of 10 polymyositis and 10 dermatomyositis patients by immunoscope, a method providing a global assessment of the T cell repert oire and a sensitive detection of clonal T cell expansions. Samples were an alyzed qualitatively and quantitatively in the blood (unsorted cells and CD 4(+) and CD8(+) cells) and in muscle infiltrates. Dramatic perturbations of the T cell repertoire were observed in the blood of polymyositis but not d ermatomyositis patients (p < 0.0005), the latter being undistinguishable fr om controls. These perturbations were due to oligoclonal expansions of CD8( +) T cells and most blood clonal expansions were also found in muscle. Thes e results indicate that the pathogenesis of polymyositis and dermatomyositi s is different and reinforce the view that polymyositis but not dermatomyos itis is an autoimmune CD8(+) T cell-mediated disease. Moreover, this method may be helpful for the differential diagnosis of polymyositis and dermatom yositis and for noninvasive follow-up of polymyositis patients.