Endogenous cytokine production protects T cells from spontaneous apoptosis during highly active antiretroviral therapy.

BACKGROUND: The availability of therapeutic regimens that effectively interfere with HIV-1 replication provides novel opportunities to investigate mechanisms of T-cell depletion as well as repopulation in infected individuals. METHODS: Nineteen HIV-1-infected individuals were investigated during one-year follow-up of highly active retroviral therapy (HAART). The frequencies of apoptotic T cells, as determined by propidium iodide, staining, TUNEL assay and analysis of annexin V, were assessed either in the absence or in the presence of anti-interleukin (IL)2 and anti-IL-4 neutralizing Ab. Spontaneous and lectin-induced cytokine production were assessed by ELISA. RESULTS: Increments of both naive and memory CD4 and CD8 T cells during HAART are accompanied by a decrease of T-cell apoptosis that, after 12 months of HAART, reaches normal levels. This is associated with increments of both spontaneous and activation-induced production of IL-2 and IL-4 by peripheral blood mononuclear cells (PBMCs), though only the latter was found defective at enrolment. During HAART, blocking of either IL-2 or IL-4 production by PBMCs using neutralizing Ab restores levels of T-cell apoptosis consistent with those determined at enrolment. These data suggest that both IL-2 and IL-4 produced by PBMCs during HAART provide anti-apoptotic signals that can contribute to an increased survival of T cells and may thus play a part in long-term immune reconstitution. CONCLUSIONS: An effective viral suppression and, possibly, effects of PI on molecular targets other than viral components, can support a progressive normalization of T-cell survival that, at least in part, depends upon the restoration of proper soluble signals. These results provide evidence of a supporting role of endogenous cytokine production in peripheral T-cell repopulation during an effective and prolonged viral suppression. This may be relevant for the definition of immune-intervention targets aimed at immune reconstitution in HIV-1-infected patients.

Decreased T cell apoptosis and T cell recovery during highly active antiretroviral therapy (HAART).

T cell apoptosis represents a common mechanism of T cell depletion in HIV-1-infected individuals reflecting maturational and functional T cell abnormalities either directly or indirectly induced by the virus. In the present study, the effects of highly active antiretroviral therapy (HAART) on the spontaneous apoptosis of distinct T cell subsets were investigated during a 6-month follow-up in a cohort of HIV-1-infected individuals with CD4(+) cell counts between 100 and 500 cells/microliter and plasma HIV-1 RNA levels >/=10, 000 copies/ml. We determined that the rapid and sustained increase of both naive (CD45RA(+)CD62L(+)) and memory (CD45R0(+) and CD45RA(+)/CD62L(-)) CD4(+) and, to as lesser extent, CD8(+) T cells in peripheral blood was associated with a significant decrease of apoptotic CD4(+) and CD8(+) as well as CD3(+)CD4(-)CD8(-) T cells. Among CD4(+) lymphocytes, at enrollment, the highest frequency of apoptotic cells was observed within the memory compartment, as defined by CD45R0 expression. During HAART, however, the frequency of CD4(+)CD45R0(+) apoptotic T cells progressively decreased in association with a significant downregulation of surface activation markers that indicated decreased levels of systemic immune stimulation. These results indicate that effective viral suppression can contribute to progressive normalization of maturational and functional T cell abnormalities responsible for the high levels of T cell apoptosis in HIV-1-infected individuals. This, in turn, may contribute to a reduced rate of T cell loss and immune reconstitution during HAART.

Inflammatory cytokines and HIV-1-associated neurodegeneration: oncostatin-M produced by mononuclear cells from HIV-1-infected individuals induces apoptosis of primary neurons.

Neurologic abnormalities are common in HIV-1-infected patients and often represent the dominant clinical manifestation of pediatric AIDS. The neurological dysfunction has been directly related to CNS invasion by HIV-1 that is principally, if not exclusively, supported by blood-derived monocytes/macrophages and lymphocytes. By using primary long term cultures of human fetal sensory neurons as well as sympathetic precursors-like neuronal cells, we determined that blood-derived mononuclear cells from HIV-1-infected individuals spontaneously release soluble mediators that can potently inhibit the growth and survival of developing neurons as well as the viability of postmitotic neuronal cells by inducing apoptotic cell death. Analysis of the cytokines produced by lymphomonocytic cells, HIV-1 infected or activated, indicated that oncostatin M (oncM) is a major mediator of these effects. Since low TGF-beta1 concentrations were capable of enhancing oncM-mediated neuronal alterations, our data indicate that by acting in concert with other cytokines, oncM may induce neuronal demise in both the developing and the mature brain. Thus, this cytokine may contribute to the setting of the neuronal cell damage observed in HIV-1-infected individuals.