Most of these litters contained one or more mice that were noticeably smaller than their littermates, some of which died prematurely (Fig. detrimental to the growth and survival of mice, restriction of hTetherin expression to hematopoietic cells gave apparently healthy mice. The expression of gamma-Mangostin hTetherin in hematopoietic cells had little or no effect on the number of MoMLV-infected splenocytes and thymocytes. However, hTetherin expression significantly reduced cell-free plasma viremia and also delayed MoMLV-induced disease. Overall, these results suggest that MoMLV spread within hematopoietic tissues and cell monolayers involves cell-to-cell transmission that is resistant to tetherin but that virion dissemination via plasma is inhibited by tetherin and is required for full MoMLV pathogenesis. IMPORTANCE Retroviruses are thought to spread primarily via direct cell-to-cell transmission, yet many have evolved to counteract an antiviral protein called tetherin, which may selectively inhibit cell-free virus release. We generated a mouse model with an inducible tetherin transgene in order to study how tetherin affects retroviral dissemination and on which cell types its expression is required to do so. We first developed a novel live-cell imaging assay to demonstrate that while tetherin does indeed dramatically reduce cell-free virus spreading, it has little to no effect on direct cell-to-cell transmission of either vesicular stomatitis virus (VSV) or the retrovirus MoMLV. Using our transgenic mouse model, we found that tetherin expression on hematopoietic cells resulted in the specific reduction of MoMLV cell-free plasma viremia but not the number of infected hematopoietic cells. The delay in disease associated with this scenario suggests a role for cell-free virus in retroviral disease progression. have yielded various results (13,C18). Moreover, studies cannot recapitulate the anatomy of virus-infected tissues in an animal host. Many studies have described the antiviral activity of tetherin effects of tetherin are often confounded by the antiviral effects of other interferon (IFN)-stimulated genes (ISGs). In mice, tetherin is constitutively expressed on only a few cell types, but it is strongly upregulated in response to type I IFN in many cells (19). LP-BM5 murine leukemia virus (MLV) infection in mice induces an IFN response (20), and replication and pathogenesis of this virus are Rabbit polyclonal to NR4A1 enhanced in tetherin-knockout mice (21). Conversely, Moloney murine leukemia virus (MoMLV) does not induce a strong type I IFN response, and tetherin knockout enhances its replication only under conditions of artificial IFN induction (21). However, a naturally occurring tetherin polymorphism that results in higher constitutive gamma-Mangostin surface expression levels correlates with reduced Friend retrovirus replication in mice gamma-Mangostin (22). In the present study, we reexamined the effects of tetherin on the spread of two enveloped viruses (MoMLV and vesicular stomatitis virus [VSV]) by using a novel live-cell imaging analysis of the simplest model of a tissue, a cell monolayer. We also examined its effects on MoMLV dissemination by using mice engineered to carry an inducible human tetherin (hTetherin) transgene. We found that tetherin severely limits cell-free virus spread to distal cells in a monolayer, while the rate of dissemination to proximal cells is largely unaffected. In the case of MoMLV, the predominant mode of spread through a monolayer is via direct cell-to-cell transmission, irrespective of tetherin expression. viral replication assay in which the two modes of virus spread could be measured and discriminated. For the initial development of assays in cultured cells, we took advantage of the known capacity of VSV to spread rapidly in monolayer cultures via both direct cell-to-cell contact and long-distance diffusion of cell-free virions (23). Because of this house, VSV titers are typically measured in PFU, using cell monolayers that are overlaid with smooth agar soon after illness to block virion diffusion through gamma-Mangostin the cell tradition supernatant. Under agar, virions generated by an in the beginning infected cell are gamma-Mangostin propagated only to adjacent cells in the monolayer, generating a roughly circular plaque whose diameter raises with time. The release of cell-free VSV particles from infected cells is definitely inhibited by tetherin (4); therefore, an initial query was whether tetherin.