To define the role of alpha/beta interferons (IFN-α/β) in simian immunodeficiency virus (SIV) infection, IFN-α and IFN-β mRNA levels and mRNA levels of Mx, an antiviral effector molecule, were determined in lymphoid tissues of rhesus macaques infected with pathogenic SIV. IFN-α/β responses were induced during the acute phase and persisted in various lymphoid tissues throughout the chronic phase of infection. IFN-α/β responses were most consistent in tissues with high viral RNA levels; thus, IFN-α/β responses were not generally associated with effective control of SIV replication. IFN-α/β responses were differentially regulated in different lymphoid tissues and at different stages of infection. The most consistent IFN-α/β responses in acute and chronic SIV infection were observed in peripheral lymph nodes. In the spleen, only a transient increase in IFN-α/β mRNA levels during acute SIV infection was observed. Further, IFN-α and IFN-β mRNA levels showed a tissue-specific expression pattern during the chronic, but not the acute, phase of infection. In the acute phase of infection, SIV RNA levels in lymphoid tissues of rhesus macaques correlated with mRNA levels of both IFN-α and IFN-β, whereas during chronic SIV infection only increased IFN-α mRNA levels correlated with the level of virus replication in the same tissues. In lymphoid tissues of all SIV-infected monkeys, higher viral RNA levels were associated with increased Mx mRNA levels. We found no evidence that monkeys with increased Mx mRNA levels in lymphoid tissues had enhanced control of virus replication. In fact, Mx mRNA levels were associated with high viral RNA levels in lymphoid tissues of chronically infected animals.
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