The effect of glycoprotein K (gK) overexpression on herpes simplex virus type 1 (HSV-1) infection in two different strains of mice was evaluated using a recombinant HSV-1 virus that expresses two additional copies of the gK gene in place of the latency-associated transcript (LAT). This mutant virus (HSV-gK ؉ T-cell response. Taken together, these results strongly suggest that increased gK levels promote eye disease and chronic infection in infected mice.

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SummaryGlycoprotein K (gK) is a virion envelope component of herpes simplex virus types 1 (HSV-1) and 2 (HSV-2), which plays an important role in virion morphogenesis and egress. We previously demonstrated that immunization of mice with gK, but not with any of the ten other HSV-1 glycoproteins, resulted in exacerbation of corneal scarring and herpetic dermatitis following ocular HSV-1 infection. However, little is known about the gK epitope(s) that is (are) involved in T cell activities in vitro or in vivo. Thus, epitope mapping of gK was performed using a panel of 15-mer peptides with five-amino-acid overlaps spanning the full-length gK, and four expressed gK recombinant proteins representing different regions of gK. Epitope mapping within the gK polypeptide defined the amino acid sequence STVVLITAYGLVLVW as the predominant CD4 + and CD8 + T cell stimulatory region both in vitro and in vivo. IFN-γ expression by CD4 + T cells was CD8 + T cells-dependent. This immunodominant epitope is located within the signal sequence of the gK polypeptide and is highly conserved in HSV-1 and HSV-2 strains. Using prediction algorithms, the peptide is predicted to bind to numerous MHC class I and class II molecules.

During HSV-1 neuronal latency, only one viral gene is consistently observed to be expressed at high levels (6, 39). This LAT (latency-associated transcript) gene has a powerful promoter that is active in most cell types (23,27,37). LAT Ϫ viruses appear to be unimpaired during acute infection (35). Thus, insertion of a foreign gene under the LAT promoter in place of the structural portion of LAT can produce a useful recombinant vector. In this study, we inserted the gene for murine interleukin-4 (IL-4) into both copies of the LAT gene (one in each viral long repeat), under control of the LAT promoter, in place of the 5Ј end of the LAT gene. The recombinant virus carrying this gene, HSV-IL-4, expressed high levels of IL-4 and allowed us to examine the effect of high exogenous IL-4 levels on HSV-1 pathogenicity in mice.IL-4 is a pleiotropic lymphokine synthesized primarily by activated T helper lymphocytes (26, 34). IL-4 enhances the development of TH2 responses and inhibits TH1 development (1,21,43). TH2 cells are involved in humoral (antibody-mediated) immunity and produce IL-4, IL-5, and IL-10 (31, 34). IL-4 is also an important regulator of isotype switching and the stimulation of immunoglobulin E production in B lymphocytes (8-10).Different reports have provided contradictory evidence suggesting that IL-4 may have either protective or detrimental effects during viral infection (4,11,12,24,29,42). Recently, a recombinant mousepox virus expressing IL-4 was reported to have greatly increased pathogenicity in infected mice (22). Even vaccinated mice were not protected against the recombinant virus.In contrast to the results with the IL-4-expressing mousepox virus, we report here that a recombinant HSV-1 expressing IL-4 had decreased pathogenicity. We found that (i) despite wild-type (wt) replication in tissue culture, HSV-IL-4 replication in mouse eyes and brains was decreased compared to that of wt virus; (ii) HSV-IL-4 infection did not kill any mice; and (iii) in mice depleted of CD4 ϩ T cells, HSV-IL-4 had wt pathogenicity, suggesting that a CD4ϩ -T-cell response was involved in protecting mice against HSV-IL-4 infection. MATERIALS AND METHODS Viruses and cells.Triple-plaque-purified wt McKrae and recombinant dLAT2903 strains of HSV-1 have been described previously (35). Rabbit skin (RS) cells, used for preparation of virus stocks, culturing mouse tear films, and determining growth kinetics, were grown in Eagle's minimal essential medium supplemented with 5% fetal calf serum. L929 cells, used for enzyme-linked immunosorbent assay titers, were grown in RPMI 1640 supplemented with 10% fetal calf serum.Mice. Inbred BALB/c, homozygous BALB/c-IL-4 Ϫ/Ϫ , and C57BL/6 mice (Jackson Laboratory, Bar Harbor, Maine) were used. All mice used were between 5 and 8 weeks old.Construction of IL-4 plasmid. The parental virus for this construct was dLAT2903, a mutant of HSV-1 strain McKrae in which the region of LAT from Ϫ161 to ϩ1667 relative to the LAT transcription start site (EcoRV-HpaI) was deleted from both copies of LAT (3...

The expression of interleukin-2 (IL-2) has been implicated in the modulation of the outcome of ocular infection with herpes simplex virus type 1 (HSV-1); however, its effects remain controversial. To clarify the role of IL-2, we constructed a recombinant HSV-1 (HSV-IL-2) that expresses two copies of the murine IL-2 gene under the control of the latency-associated transcript (LAT) promoter of HSV-1 in a LAT-negative virus. In tissue culture, the replication of the HSV-IL-2 was 100-fold lower than that of the wild-type virus at a low multiplicity of infection (MOI). Addition of recombinant anti-IL-2 polyclonal antibody markedly enhanced HSV-IL-2 replication in tissue culture. In the 7-day period after ocular infection of BALB/c mice, the replication of HSV-IL-2 was significantly lower than that of wild-type virus in tear cultures, whole eyes, and brain, but was equivalent to wild-type replication in the trigeminal ganglia. Ocular challenge of BALB/c mice with HSV-IL-2 alone, at an MOI that resulted in only 13% survival when parental virus was used, was associated with 90% survival. This decrease in virulence was further shown to be attributable to the expression of IL-2 by coinfection of mice with HSV-IL-2 and the parental virus. This resulted in a decrease in virulence of the parental virus (5% survival when administered alone versus 50% survival on coinfection with HSV-IL-2). The survival of HSV-IL-2-infected mice was compromised by depletion of either IL-2, CD4؉ , or CD8 ؉ T cells (50% survival) and abolished completely by depletion of both T-cell subtypes. Moreover, depletion of CD4 ؉ T cells, CD8 ؉ T cells, or both increased the titers of HSV-IL-2 in the tears, eyes, trigeminal ganglia, and brains of infected mice, so that titers were equivalent to or higher than that of the parental virus. These results suggest that IL-2 expression by recombinant HSV-1 reduces virulence and that depletion of IL-2 or T cells increases virulence in HSV-1-infected mice.