The Roles of Chemokines in Rabies Virus Infection: Overexpression May Not Always Be Beneficial

Abstract

It was found previously that induction of innate immunity, particularly chemokines, is an important mechanism of rabies virus (RABV) attenuation. To evaluate the effect of overexpression of chemokines on RABV infection, chemokines macrophage inflammatory protein 1␣ (MIP-1␣), RANTES, and IP-10 were individually cloned into the genome of attenuated RABV strain HEP-Flury. These recombinant RABVs were characterized in vitro for growth properties and expression of chemokines. It was found that all the recombinant viruses grew as well as the parent virus, and each of the viruses expressed the intended chemokine in a dose-dependent manner. When these viruses were evaluated for pathogenicity in the mouse model, it was found that overexpression of MIP-1␣ further decreased RABV pathogenicity by inducing a transient innate immune response. In contrast, overexpression of RANTES or IP-10 increased RABV pathogenicity by causing neurological diseases, which is due to persistent and high-level expression of chemokines, excessive infiltration and accumulation of inflammatory cells in the central nervous system, and severe enhancement of blood-brain barrier permeability. These studies indicate that overexpression of chemokines, although important in controlling virus infection, may not always be beneficial to the host.Rabies virus (RABV) is a negative-strand RNA virus belonging to the Rhabidoviridae family, genus Lyssavirus, which causes rabies (fatal encephalomyelitis) in many species of mammals (5). More than 55,000 humans die of rabies each year worldwide (26). Once clinical signs develop, rabies is always fatal (12, 53). Despite the lethality of rabies, only mild inflammation and little neuronal destruction were observed in the central nervous system (CNS) of rabies patients (31, 32). Adaptation of wild-type (wt) RABV in laboratory animals and/or cell culture leads to attenuation in phenotype, and laboratory-adapted RABVs have been used for vaccine development (1, 10). To delineate the mechanism(s) of RABV attenuation, previous studies compared the host responses to infection with either laboratory-attenuated or wt RABV (52). It was found that laboratory-attenuated RABV induced extensive inflammation, apoptosis, and neuronal degeneration, as well as induction of expression of innate immune genes in the CNS; however, wt RABV caused little or no neuronal damage and avoided the activation of expression of innate molecule genes. Other investigators also reported the induction of innate immunity in mice or neuronal cells infected with laboratory-attenuated viruses (20,33,37). The mostly upregulated genes in the innate immune responses after infection with attenuated RABV include genes encoding for inflammatory chemokines and type I interferon (IFN) as well as 33, 378). Further studies have shown that the expression of chemokines (mRNA and proteins), particularly macrophage inflammatory protein 1␣ (MIP-

Ambivalent Role of the Innate Immune Response in Rabies Virus Pathogenesis

“…This observation, together with previous studies investigating the role of IFN in rabies (28,33,36), questions the efficiency of IFN in controlling RABV infection in the NS. In the same vein, since several studies have pointed out that infiltrating T cells recruited into the brain by chemokines have a direct antiviral effect on RABV infection (14,19,59), it was expected that mice exhibiting reduced T cell infiltration, as LGP2 TG mice do, would be less able to control RABV spread in the NS than WT mice. In striking contrast, LGP2 TG mice, not WT mice, eliminated RABV infection from the brain at day 11 p.i.…”

A Novel Rabies Vaccine Expressing CXCL13 Enhances Humoral Immunity by Recruiting both T Follicular Helper and Germinal Center B Cells

“…Viruses were titrated via direct fluorescent antibody assays in BSR cells as described previously (11). Briefly, BSR cells seeded in 96-well plates were inoculated with serial 10-fold dilutions of the virus and incubated at 37°C for 3 days.…”

Enhancement of Blood-Brain Barrier Permeability and Reduction of Tight Junction Protein Expression Are Modulated by Chemokines/Cytokines Induced by Rabies Virus Infection

“…CVS-B2c is a RABV that was attenuated in the laboratory by passaging the challenge virus standard (CVS-24) in baby hamster kidney (BHK21) cells (31). The recombinant virus HEP-CXCL10 (rHEP-CXCL10) was constructed in our laboratory previously (7). A fluorescein isothiocyanate (FITC)-conjugated anti-RABV nucleoprotein antibody was obtained from Fujirebio (Malvern, PA).…”

“…In the mouse model, inflammation is mild after infection with wild-type (wt) RABV (6). However, extensive inflammation, apoptosis, and expression of innate immune genes have been found in the CNSs of mice infected with laboratory-attenuated RABV (7)(8)(9)(10)(11)(12). Recently, it has been found that blood-brain barrier (BBB) permeability is enhanced in mice infected with laboratory-attenuated, but not wt, RABV (10,13).…”