Background
The non-pathogenic course of SIV infection in its natural host is characterized by robust viral replication in the absence of chronic immune activation and T cell proliferation. In contrast, acutely lethal enteropathic SIVsmm strain PBj induces a strong immune activation and causes a severe acute and lethal disease in pig-ta
iled macaques after cross-species transmission. One important pathogenicity factor of the PBj virus is the PBj-Nef protein, which contains a conserved diacidic motif and, unusually, an immunoreceptor tyrosine-based activation motif (ITAM).
Results
Mutation of the diacidic motif in the Nef protein of the SIVsmmPBj abolishes the acute phenotype of this virus.
In vitro, w
ild-type and mutant PBj (PBj-Nef202/203GG) viruses replicated to sim
ilar levels in macaque PBMCs, but PBj-Nef202/203GG no longer triggers ERK mitogen-activated protein (MAP) kinase pathway including an alteration of a Nef-associated Raf-1/ERK-2 multiprotein signaling complex. Moreover, stimulation of IL-2 and down-modulation of CD4 and CD28 were impaired in the mutant virus. Pig-ta
iled macaques infected with PBj-Nef202/203GG did not show enteropathic complications and lethality as observed with w
ild-type PBj virus, despite efficient replication of both viruses
in vivo. Furthermore, PBj-Nef202/203GG infected animals revealed reduced T-cell activation in periphery lymphoid organs and no detectable induction of IL-2 and IL-6.
Conclusions
In sum, we report here that mutation of the diacidic motif in the PBj-Nef protein abolishes disease progression in pig-ta
iled macaques despite efficient replication. These data suggest that alterations in the ab
ility of a lentivirus to promote T cell activation and proliferation can have a dramatic impact on its pathogenic potential.
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