Abstract
Simian T-cell lymphotropic viruses (STLV), the nonhuman primate counterparts of human T-cell lymphotropic viruses (HTLV), are endemic in many populations of African and Asian monkeys and apes. Although an etiologic link between STLV1 infection and lymphoproliferative disorders such as malignant lymphomas has been suggested in some nonhuman primate species, most STLV infections are inapparent, and infected animals remain clinically healthy. The retroviral transactivator, tax, is well known to increase transcription of viral and cellular genes, resulting in altered cytokine profiles. This study compared the cytokine profiles of peripheral blood mononuclear cell (PBMC) cultures from 25 STLV1-seropositive rhesus macaques (Macaca mulatta) with those of age- and sex-matched seronegative controls. IFNγ, TNFα, IL10, and IL2 levels in unstimulated PBMC culture supernatants were measured at 24, 48, and 72 h by using enzyme immunoassays. IFNγ concentrations were found significantly higher in the supernatants of PBMC cultures of seropositive monkeys as compared with seronegative controls. In addition, although IL2 concentrations were not significantly elevated in the supernatants of PBMC cultures of all seropositive monkeys as compared with all seronegative controls, IL2 levels were increased in a subset of 5 pairs. Increased constitutive cytokine release occurred in the absence of spontaneous proliferation. The increased constitutive release of IFNγ and IL2 suggests that STLV1 alters immune functions in infected but clinically healthy rhesus macaques and further characterizes STLV1 infection of rhesus macaques as a potential model for human HTLV1 infection.