Systemic sclerosis immunoglobulin G autoantibodies bind the human cytomegalovirus late protein UL94 and induce apoptosis in human endothelial cells

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Abstract
Systemic sclerosis is an autoimmune disease characterized by immunological and vascular abnormalities. Autoantibodies against intracellular antigens are associated with particular clinical features of the disease1, whereas autoantibodies against cell surface antigens may be pathogenic by inducing endothelial cell damage2,3, considered the primary event in the pathogenesis of the disease. Latent human cytomegalovirus infection may contribute to progression of systemic sclerosis through its ability to infect endothelial cells4; however, direct links between human cytomegalovirus infection and systemic sclerosis are still lacking5. Molecular mimicry is one of the mechanisms that account for the link between infection and autoimmunity6,7,8. Here we have identified an immunodominant peptide using systemic sclerosis serum screening of a random peptide library; such peptide shares homology with autoantigens and with the human cytomegalovirus late protein UL94 (ref. 9). Immunoglobulin G antibodies against the peptide affinity-purified from the sera of patients with systemic sclerosis specifically recognized the viral product and autoantigens; moreover, such antibodies induced endothelial cell apoptosis through specific interaction with the cell surface integrin–NAG-2 protein complex10. Our results provide evidence that antibodies against human cytomegalovirus cause apoptosis of endothelial cells11, considered the initial pathogenic event of systemic sclerosis, and indicate a previously unknown mechanism for the etiological link between human cytomegalovirus infection and autoimmunity.