Decreased reactivation of a herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) mutant using the in vivo mouse UV-B model of induced reactivation

Abstract

Blinding ocular herpetic disease in humans is due to herpes simplex virus type 1 (HSV-1) reactivations from latency, rather than to primary acute infection. The cellular and molecular immune mechanisms that control the HSV-1 latency-reactivation cycle remain to be fully elucidated. The aim of this study was to determine if reactivation of the HSV-1 latency-associated transcript (LAT) deletion mutant (dLAT2903) was impaired in this model, as it is in the rabbit model of induced and spontaneous reactivation and in the trigeminal ganglia (TG) explant-induced reactivation model in mice. The eyes of mice latently infected with wild-type HSV-1 strain McKrae (LAT((+)) virus) or dLAT2903 (LAT((-)) virus) were irradiated with UV-B, and reactivation was determined. We found that compared to LAT((-)) virus, LAT((+)) virus reactivated at a higher rate as determined by shedding of virus in tears on days 3 to 7 after UV-B treatment. Thus, the UV-B-induced reactivation mouse model of HSV-1 appears to be a useful small animal model for studying the mechanisms involved in how LAT enhances the HSV-1 reactivation phenotype. The utility of the model for investigating the immune evasion mechanisms regulating the HSV-1 latency/reactivation cycle and for testing the protective efficacy of candidate therapeutic vaccines and drugs is discussed.

Keywords: Animal model; Eye; HSV-1; Immunology; LAT; Recurrent herpetic disease; UV-B; Virology.

Figure 1. Schematic representation of the time line used in the UV-B model

Mice were infected with HSV-1 as described in Materials & Methods closely adhering to the published model as shown in a video (Morris et al, 2012a). Tears were collected on the indicated days (days 0-7). Eye disease was scored on the indicated days (days 10, 17, 31).

Figure 2. UV-B induced reactivation of virus from mice latently infected with HSV-1 strain McKrae

Mice were infected and ~30 days later when latency was well established, virus was induced by UV-B irradiation of eyes as described in Materials & Methods and (Morris et al, 2012a). Panel A: The cumulative percent of eyes that shed UV-B induced reactivated virus within one week of UV-B irradiation. Panel B: The cumulative percent of virus positive cultures (daily eye swabs plated on indicator cells). Expt. 1: Results of the right eyes of 9 mice. Expt. 2: Results of both eyes from 10 mice (20 eyes).

Figure 3. Recurrent eye disease following UV-B irradiation

The eyes from the experiment 1 shown in figure 2 were monitored for eye disease (clouding on a scale of 0 to 4 (Morris et al, 2012a)) on days 10, 17, and 31 post UV-B irradiation. Groups: wt McKrae, 15 eyes; Control, naïve age matched mice receiving the same UV-B irradiation treatment, 20 eyes. “**” Indicates highly significant differences on that day with a P value <0.001 as determined by a two sided Fisher exact test.

Figure 4. UV-B induced reactivation of LAT⁽⁺⁾ versus LAT⁽⁻⁾ virus

Fifteen mice/group (30 eyes) were infected, subjected to UV-B irradiation 30 days p.i., and induced reactivation analyzed as described in the legend to Figure 2. P values were determined by 2-sided Fisher exact test.