Experimental keratitis in rabbits by human HSV‐1 variants: Prevention and treatment

Abstract

The efficacy of different therapies and vaccine preparations was assessed for treating or preventing herpetic ocular keratitis induced by experimental inoculation in rabbits with two HSV-1 variants that display different pathogenetic potential. Early administration of acyclovir (ACV) promoted fast healing and prevented neurologic involvements: alpha-interferon (alpha-IFN) was less efficient than ACV; combined therapy with both drugs increased the antiviral effects. In an attempt to prevent the disease, rabbits were vaccinated with a slightly pathogenic HSV-1 variant or with a secreted form of an engineered HSV-1 glycoprotein gB (gB-1s) and were subsequently challenged with a highly pathogenic HSV-1 variant. Immunization of rabbits with gB-1s was much more efficient than immunization with live virus in reducing the severity of herpetic keratitis and in preventing CNS disease.

Effects of the Passive Transfer of Anti-gB Antibodies in a Rabbit Model of HSV-1 -Induced Keratitis

“…As previously reported [8], the immunization of rabbits with gBl-s associated with an immunologic adjuvant provided a high degree of protection against herpetic disease, whatever the adjuvant utilized: in fact, an aluminum hydroxide solu tion was used in this case, while previous experiments were performed using Freund's complete adjuvant. In this trial, gBl-s vaccination proved very effective, both in preventing CNS involvement and animal death as well as in reducing the severity and time course o f LV herpetic keratitis.…”

“…Fifty microlitcrs o f virus suspension (containing I05 PFU) was introduced in the con junctival sac and gently massaged onto the eye with the eyelids [7], For 16 days or until the animals died, eye scores were read at 2-day intervals, using a cobalt-filtered blue light on eyes previously stained with fluorescein. Corneal lesions were graded on a scale o f 0 to +5 according to the surface area involved, as previously described [8], The eyes were photographed with a Contax camera equipped with a macrolens.…”

“…For these reasons, they have been the focus of most immunological and vaccine studies. gD immunization has proved to protect mice from both the development of stromal keratitis and its spread to the CNS [9,13]; however, in rabbits it could not reduce the incidence of latency, although it did provide some protection against epithelial and stromal keratitis [10], As regards gB, previous results have shown that immunization with a secreted form of gB from HSV-1 (gBl-s) could protect mice against lethal, latent and recurrent HSV-1 infections [11], and in rabbits it was very efficient in preventing CNS disease and in reduc ing the severity of keratitis [8]. Furthermore, among viral glycoproteins, gB and gD have been shown to elicit the highest neutralizing antibody titers, thus offering the best protection against lethal challenge and establishment of la tency in mice [12],…”

“…Therefore, immunization has been considered the most de sirable approach to limiting the disease and preventing pri-mary and/or latent infections. Positive results have been ob tained both with live, attenuated or inactivated virus vac cines [5][6][7][8] and with subunit vaccines, prepared from purified HSV glycoproteins [8][9][10][11][12]. Particularly the latter approach has been extensively developed because o f its comparable safety over the use of attenuated viruses, which neither offer complete protection from ocular involvement nor prevent latency.…”

“…For this reason and as the rabbit response to drug ther apy correlates well with that in humans [2,21], this experi mental model was chosen to test the effectiveness of passive immunization in preventing herpetic disease. For passive transfer experiments, antibodies directed against gBl-s were used, as this glycoprotein had previously shown a high immunogenicity in active immunization trials [8,11]. Rab bits were immunized by intramuscular injection of homolo gous polyclonal serum against gBl-s, given before, simulta neously or after the ocular challenge with a large, highly pathogenic, plaque variant of HSV-1 (large variant, LV) [22], In rabbits, this variant produces a stromal keratitis with neurological involvement, resulting in encephalitis and death of the animal [7].…”