Immunophenotypic characterization of the cutaneous exanthem of SIV-infected rhesus monkeys. Apposition of degenerative Langerhans cells and cytotoxic lymphocytes during the development of acquired immunodeficiency syndrome

A T-cell tropic retrovirus, simian immunodeficiency virus (SIV), has recently been isolated from immunodeficient rhesus monkeys. This virus has remarkable similarities to human immunodeficiency virus (HIV), the etiologic agent of acquired immunodeficiency syndrome. Subsequent studies of simian infection with SIV have shown it to be a relevant animal model for studying the pathogenesis of AIDS in man. In both HIV-infected humans and SIV-infected monkeys, a cutaneous maculopapular eruption has been described. To date, the pathogenesis and possible relationship of these exanthema to the evolution of systemic immunosuppression have remained obscure. In this study, the mononuclear cell infiltrates that characterize skin rashes of SIV-infected rhesus monkeys were found to be composed predominantly of cells with phenotypic characteristics of cytotoxic/suppressor (T8⁺) lymphocytes and natural killer cells. Many of these cells expressed membrane-bound interleukin-2 receptor molecules. Double labeling and immunoelectron microscopy revealed these cells in direct contact with degenerative Langerhans cells within the epidermis and dermis. These observations suggest that the cutaneous rash associated with SIV infection may be the consequence of target cell injury of Langerhans cells by effector cells with cytotoxic potential.