Abstract
The xenotropic/polytropic subgroup of mouse leukemia viruses (MLVs) all rely on the XPR1 receptor for entry, but these viruses vary in tropism, distribution among wild and laboratory mice, pathogenicity, strategies used for transmission, and sensitivity to host restriction factors. Most, but not all, isolates have typical xenotropic or polytropic host range, and these two MLV tropism types have now been detected in humans as viral sequences or as infectious virus, termed XMRV, or xenotropic murine leukemia virus-related virus. The mouse xenotropic MLVs (X-MLVs) were originally defined by their inability to infect cells of their natural mouse hosts. It is now clear, however, that X-MLVs actually have the broadest host range of the MLVs. Nearly all nonrodent mammals are susceptible to X-MLVs, and all species of wild mice and several common strains of laboratory mice are X-MLV susceptible. The polytropic MLVs, named for their apparent broad host range, show a more limited host range than the X-MLVs in that they fail to infect cells of many mouse species as well as many nonrodent mammals. The co-evolution of these viruses with their receptor and other host factors that affect their replication has produced a heterogeneous group of viruses capable of inducing various diseases, as well as endogenized viral genomes, some of which have been domesticated by their hosts to serve in antiviral defense.
Highlights
Gammaretroviruses of three distinct host range tropisms have been isolated from the laboratory mouse (Table 1)
While the mouse X-mouse leukemia viruses (MLVs) are generally able to infect all mammals, XMRV is uniquely restricted by Chinese hamster and gerbil cells (Table 3), a restriction associated with sequence differences in the receptor determining region of Xpr1 ECL4 [101]
Multiple examples of xenotropism exist among the retroviruses
Summary
Gammaretroviruses of three distinct host range tropisms have been isolated from the laboratory mouse (Table 1). Inbred strains of laboratory mice tend to carry multiple copies of both Xmvs and M/Pmvs, these virus subtypes are largely segregated into different species in the house mouse complex [71] (Figure 1, 2 and 3). Some of the wild mouse ERVs are active, and infectious viruses of xenotropic or atypical host ranges have been isolated from lymphoid tissues or cultured cells of Eurasian species and from mice trapped in California [57,75,76,77,78,79] (Figure 2). The various X/P-MLVs isolated from laboratory and wild mouse species differ phenotypically on the basis of host range, variable reactivity with antiMLV antibodies, cross-interference, cytopathicity, and pathogenicity in mice Sequence data for these viruses is limited, but comparisons of available env sequences indicate there is significant heterogeneity, in the RDB of the Env glycoprotein.
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