Development of lymphoid hyperplasia in transgenic mice expressing the HIV tat gene.

During HIV infection, individuals experience multiorgan disorders such as adenopathy, splenomegaly, and lung and brain diseases. There is an increasing body of evidence that the HIV trans-activating tat gene product possesses multiple activities. First, it can activate several cellular genes; second, in its extracellular soluble form, it plays the role of growth factor in some cells such as Kaposi's sarcoma cells. Thus, we introduced the HIV tat gene, under the control of the cellular proteolipoprotein promoter, into the germline of mice and demonstrate that, when expressed, the tat gene product induces lymphoid hyperplasia in spleen, lymph nodes, and lung, as is observed in AIDS patients, but not in the brain or testes. Our findings indicate that HIV, through some of its genes, directly participates in the pathogenesis of AIDS.

The basic domain of the lentiviral Tat protein is responsible for damages in mouse brain: involvement of cytokines.

The HIV and visna lentiviruses induce an inflammatory reaction in the central nervous system (CNS) of the infected hosts leading to dysmyelination, demyelination, and neuronal loss. The basic domain of the transactivating Tat protein has been involved in CNS damage. Infusion of basic containing domain Tat peptides in the lateral ventricle (systemic injection) or in the grey matter, i.e., hippocampus and thalamus (local injection), induced an inflammatory process characterized by the formation of an edema and invasion of macrophage accompanied by reactive astrogliosis. Control peptides originating from either lentiviral proteins or irrelevant protein as ovalbumin did not lead to any inflammatory reaction or cell death. The inflammation led to the loss of ependymal cells in the lateral ventricles and neurons in the grey matter. RNA extracted from the Tat-injected hemisphere reacted with TNF-alpha, IL-1 alpha and beta, and IL-6 probes. The macrophage/microglia inducible nitric oxyde synthase was also expressed. Blockade of TNF-alpha by a pentoxifylline treatment led to the decrease of IL-1 and iNOS expression accompanied by a reduction of the volume of the lesions indicating that the Tat-induced lesions might be mediated by TNF production.

The maedi-visna virus Tat protein induces multiorgan lymphoid hyperplasia in transgenic mice.

Sheep infected with maedi-visna virus experience immunological disorders leading to progressive chronic diseases involving the brain, lung, spleen, and lymph nodes. To study the biological activity of the viral transactivating Tat protein, we generated transgenic mice carrying the tat gene. Analysis of the transgenic mouse tissues for tat mRNA revealed that while low at the messenger level, the expression of the transgene correlated with dramatic follicular lymphoproliferative disorders involving the lung, spleen, lymph nodes, and skin. This finding suggests that the viral protein possesses a high pathological potency. Our findings show that the maedi-visna virus tat gene product contributes to the pathogenesis of multiorgan proliferative disorders associated with maedi-visna virus infection.