The newly discovered type III interferon lambda (IFN-lambda) has antiviral activity against a broad spectrum of viruses and potent immune-related activities. Its major producers are peripheral blood mononuclear cells (PBMCs) and dendritic cells. The above functions and cells are deeply involved in AIDS pathogenesis, but there is no information so far on IFN-lambda effects on HIV. Therefore we addressed the sensitivity of HIV-1 replication to cell exposure to human IFN-lambda2. Human PBMCs and C8166 T cells were treated with human Type III or Type I IFNs, and the ability of HIV-1 to bind and replicate in untreated and IFN-treated cells was investigated. Virus amounts were quantified by infectivity and p24 assays. In parallel, we evaluated the possible antiproliferative effects of IFN-lambda2 and the expression of CD4, CXCR4, and CCR5 genes, whose transcripts were quantified by real time RT-PCR. Data showed increased adsorption of HIV to IFN-treated cells in a dose-dependent fashion. Virus yields increased accordingly. In both systems the accumulation of CD4, CXCR4, and CCR5 transcripts was increased, particularly in PBMCs. Antiproliferative activity and classical antiviral state were instead detected on PBMCs, but not on C8166 cells. We concluded that pretreatment of PBMCs and C8166 cells with Type III and Type I IFNs causes increased HIV binding and replication. These effects are likely to be due to increased expression of HIV receptors and coreceptors on the plasma membrane. These findings indicate another mechanism utilized by HIV for subversion of host defenses.