Cell-Mediated Immune Response to Human T-Lymphotropic Virus Type I

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Abstract
Human T-lymphotropic virus type I (HTLV-I) is a retrovirus that causes persistent infection in many populations in tropical and subtropical regions. HTLV-I chronically activates the cell-mediated arm of the host adaptive immune response. There has been much debate about the role of the immune response in determining the outcome of HTLV-I infection: most seropositive individuals remain lifelong asymptomatic carriers of the virus, whereas a small proportion—usually those with higher equilibrium proviral loads—develop an inflammatory disease of the central nervous system known as HAM/TSP. Here we discuss the cell-mediated immune response to HTLV-I infection. We summarize recent data on the HTLV-I–specific CD4+ cell response and explore its potential role in HAM/TSP pathogenesis. We also explore the controversy surrounding the role of the CD8+ cell response in controlling HTLV-I infection and/or contributing to HAM/TSP disease, highlighting recent studies of T cell gene expression profiles and a newly developed assay of CD8+ cell functional efficiency. Finally, we introduce a possible role for cellular innate immune effectors in HTLV-I infection.