HIV Type 1 Induction of Interleukin 1 and 6 Production by Human Thymic Cells

Abstract

In vitro and in vivo studies have demonstrated that HIV can infect thymocytes at different maturational stages and lead to changes in the thymic microenvironment. To determine the effect of HIV on thymic stromal cells and the production of cytokines important in thymocyte development, three types of adherent thymic cultures were established and studied: thymic epithelial cells (TECs), macrophage-enriched, and mixed cultures of macrophages and TECs (Mφ/TEC). Cultures were exposed to HIV-1 strains HIV-1_IIIB and HIV-1_Ba-L, and studied from day 2 to day 26 for the presence of infection, cytopathology, and cytokine (IL-1α, IL-1β, and IL-6) production. Mφ/TEC and macrophage-enriched cultures were infected by both HIV strains without cytopathic changes. The TECs grew well in culture for at least 6 weeks and showed no evidence of infection, cytopathology, or changes in cytokine production with HIV. Only cultures containing macrophages (Mφ/TEC or macrophage enriched) showed changes in cytokine production with HIV. Sustained production of IL-1α was seen for up to 20 days, with small or no increases in IL-1β. Mφ/TEC and TEC cultures produced high constitutive levels of IL-6 that were not changed by HIV. Unstimulated macrophage-enriched cultures produced small amounts of IL-6 that were increased by HIV 20-fold. This study suggests that HIV infection in vivo can lead to infection of thymic macrophages resulting in cytokine abnormalities and a constant source for HIV to infect maturing thymocytes. These cytokine effects could lead to abnormal maturation and contribute to the lack of regeneration of the mature CD4⁺ T cell pool.