The roles of chemokines on rabies virus pathogenicity and immunogenicity
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It has been found previously that induction of innate immunity is an important mechanism of rabies virus (RABV) attenuation. To evaluate the effect of overexpression of innate immune molecules on RABV immunogenicity, chemokines MIP-1α, RANTES and IP-10 were initially cloned into the genome of attenuated RABV strain HEP-Flury. These recombinant RABVs were evaluated in the mouse model for virulence and immunogenicity. It was found that overexpression of MIP-1α further attenuated RABV virulence when compared to the parental RABV. On the other hand, overexpression of RANTES and IP-10 increased RABV virulence by inducing excessive infiltration of immune cells into the CNS, especially CD3+ T cells and neutrophils. Furthermore, up-regulation of RANTES and IP-10 enhanced blood-brain-barrier (BBB) permeability. Immunization of mice with the recombinant HEP- MIP1α by the intramuscular route induced significantly higher titers of virus neutralizing antibodies (VNA) and provided more protection against lethal challenge than with parental virus, HEP-MIP1α (–) virus, as well as viruses expressing RANTES or IP-10. Our data thus demonstrate that overexpression of chemokines are not always beneficial during RABV infection. Expression of MIP-1α can induce innate and enhance adaptive immune responses against rabies while further attenuate RABV virulence. On the other hand, over-expression of RANTES or IP-10 increased RABV virulence. Together, these studies indicate that overexpression of MIP-1α can further attenuate RABV virulence and enhance RABV immunogenicity and thus HEP- MIP1α have the potential to be developed as live avirulent RABV vaccines.