Acute and latent herpes simplex virus neurological disease in mice immunized with purified virus-specific glycoproteins gB or gD

Groups of 5-week-old BALB/c mice were immunized intraperitoneally with approximately 10 micrograms of purified alum-precipitated glycoprotein gB or gD of either herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2) origin. Control mice received injections of alum-precipitated 1% bovine serum albumin (BSA). Following a second immunization 4 weeks later, seroconversion was confirmed by demonstrating the presence of glycoprotein-specific antibody by immune precipitation. All animals were challenged with lethal doses of either HSV-1 or HSV-2 by footpad inoculation and assessed for acute virus-induced neurological disease and the development of ganglionic latency. Whereas 70% of control (BSA-immunized) HSV-1-infected animals developed ascending myelitis and died, 100% of mice immunized with either gB-1, gB-2, gD-1, or gD-2 antigens remained free of clinical illness and survived HSV-1 challenge. In contrast, gB-1-or gB-2-immunized mice were not protected against acute HSV-2-induced neurological disease and showed a mortality rate of 60-90% (equivalent to that seen in controls), although mean survival times were prolonged. However, significant protection against HSV-2 challenge was observed with gD-1 or gD-2 immunization. When sacral ganglia were removed from surviving mice 9-12 months after virus challenge, latent virus was detected in all gB- or gD-immunized animals, although the extent of latent infection was restricted. These results provide evidence that glycoprotein gD might be superior to glycoprotein gB as an immunogen for the control of acute HSV-1 and HSV-2 neurological disease in mice. However, neither glycoprotein prevents ganglionic latency, the source of virus for recurrent herpesvirus infections.     

Use of monoclonal antibodies for analysis of antibody-dependent immunity to ocular herpes simplex virus type 1 infection.

Monoclonal antibodies specific for the five major glycoproteins of herpes simplex virus type 1 (HSV-1) were tested for their capacity to mediate immunity to ocular HSV-1 infection. The specificity of the immunoglobulin made by each monoclone was determined by immunoprecipitation of [14C]glucosamine-labeled polypeptides from detergent-solubilized HSV-1-infected cells. Of the five monoclonal antibodies studied, two immunoprecipitated glycoproteins gA/B, one immunoprecipitated glycoprotein gC, one immunoprecipitated glycoprotein gD, and one immunoprecipitated glycoprotein gE. All five were effective in passively transferring immunity to mice when they were given 4 to 24 h after HSV-1 infection on an abraded cornea. Four of the monoclonal antibodies were also evaluated for their capacity to neutralize HSV-1 and to promote complement-mediated cell lysis and antibody-dependent cellular cytotoxicity. It was found that none of these in vitro assays correlated with the protective activity of the antibodies in vivo. In fact, one of the monoclonal antibodies was unreactive in all three immunological reactions, even though it was highly effective in promoting recovery from HSV-1 induced ocular disease in vivo. The results suggest that antibodies can interact in vivo with virus-specific glycoproteins gA/B, gC, gD, and gE to initiate recovery from HSV-1-induced ocular disease, and that the therapeutic effectiveness of a specific monoclonal antibody does not correlate with its immunological reactivity in vitro.     

Detection of type-specific antibody to herpes simplex virus type 1 by radioimmunoassay with herpes simplex virus type 1 glycoprotein C purified with monoclonal antibody.

Herpes simplex virus type 1 (HSV-1) and HSV-2 specify at least four glycoproteins designated gA/gB, gC, gD, and gE. Previous studies have shown that gC produced by HSV-1 is antigenically distinct from the corresponding HSV-2 glycoprotein. With the exception of gC, the glycoproteins of both serotypes share antigenic sites. Standard serological assays fail to differentiate the antibody to the shared antigenic determinants from the type-specific antibody. In this paper, we describe a procedure for purifying gC from HSV-1-infected cell extracts with an immunoadsorbent prepared with an HCL monoclonal antibody. When used in a solid-phase radioimmunoassay, gC proved to be a type-specific antigen for quantitation of antibody to HSV-1. Among individuals who had no antibody to HSV at the onset of infection, all of those with primary HSV-1 infection developed antibody to gC. Subjects with primary HSV-2 infection failed to develop antibody reactive with gC of HSV-1 (P less than 0.01). Both immunoglobulin G and M antibodies against gC were detected in sera from subjects with either primary or recurrent HSV-1 infection. Higher antibody titers to gC were found in sera from individuals with recurrent infection than in sera from those with primary HSV-1 infection.     

Antibody-mediated recovery from subcutaneous herpes simplex virus type 2 infection.

Young adult mice infected with 3 X 10(6) plaque-forming units of herpes simplex virus type 2 (HSV-2) died within 9 to 12 days after spread of the virus from the sites of infection to the spinal cord and brain. Administration of HSV-2-neutralizing antisera prepared in syngenic mice or in rabbits inhibited spread of the virus from the footpad of infected animals and prevented death. A single intraperitoneal inoculum of antiserum (virus-neutralizing titer of 1:128) was effective in protecting mice when the antiserum was given at 8 to 48 h, but not at 72 h, after virus inoculation. Immune sera absorbed with HSV-2-infected cells no longer protected mice from subcutaneous infection, whereas absorption with noninfected cells had no effect. Thus, HSV-2-specific antibodies appeared to be responsible for the protection observed. If the mice were given a sublethal dose of irradiation (390 rads) at 24 h before antibody transfer, protection was no longer obtained. This suggested that the mechanism of protection probably was not solely due to in vivo neutralization of virus, but required the participation of a radiosensitive component which has not yet been defined.     

Estimation of the B lymphocyte precursor frequencies to herpes simplex type 1 glycoproteins by a limiting dilution assay

The precursor frequency of B lymphocytes from Balb/c mice producing HSV-1 glycoprotein B (gB), glycoprotein C (gC), and glycoprotein D (gD) antibody was determined by limiting dilution analysis under conditions to detect antibody from the clonal progeny of a single B cell precursor. In spleens of naive mice the average gC frequency was 1/48,917 +/- 5,550, while gD was 1/73,330 +/- 15,898, and gB frequency was in excess of 1/100,000. Immunization with live HSV-1 (KOS) increased the B cell frequencies of all three glycoproteins to approximately 1:3,000; however, the serum gB antibody ELISA titer was fivefold higher than gC or gD.     

表达单纯疱疹病毒Ⅱ型糖蛋白D的重组痘苗病毒活疫苗…

我们以前曾报道，表达单纯疱疹病毒Ⅱ型糖蛋白的重组痘苗病毒能保护被免疫小鼠抵抗致死量ＨＳＶ－２病毒的攻击。在此工作基础上，严格按人用疫苗研究要求的实验条件，成功地建立了表达ＨＳＶ－２ｇＤ的重组痘苗病毒活疫苗株，首先将经聚合酶链反应修饰的ＨＳＶ－２ｇＤ基因插入痘苗表达质粒ｐＪＳＢ１１７５，置于痘苗病毒Ｐ７．５Ｋ早／晚期启动子控制下，将同位重组质粒用Ｌｉｐｏｆｅｃｔｉｎ方法转染已受野型ＴＫ＾＋痘苗病毒天     

表达单纯疱疹病毒Ⅱ型糖蛋白D的重组痘苗病毒活疫苗株的建立

我们以前曾报道，表达单纯疱疹病毒Ⅱ型糖蛋白Ｄ（ＨＳＶ－２ｇＤ）的重组痘苗病毒（实验疫苗株）能保护被免疫小鼠抵抗致死量ＨＳＶ－２病毒的攻击。在此工作基础上，严格按人用疫苗研究要求的实验条件，成功地建立了表达ＨＳＶ－２ｇＤ的重组痘苗病毒活疫苗株。首先将经聚合酶链反应（ＰＣＲ）修饰的ＨＳＶ－２ｇＤ基因插入痘苗表达质粒ｐＪＳＢ１１７５，置于痘苗病毒Ｐ７５Ｋ早／晚期启动子控制下。将此重组质粒用Ｌｉｐｏｆｅｃｔｉｎ方法转染已受野型ＴＫ＋痘苗病毒天坛７６１株感染的人胚肺二倍体细胞。经同位素探针（３２Ｐ－ＨＳＶ－２ｇＤ）原位杂交法和３轮蚀斑纯化，筛选出基因组内整合有ＨＳＶ－２ｇＤ基因的重组痘苗病毒。斑点和Ｓｏｕｔｈｅｒｎ杂交证实，ＨＳＶ－２ｇＤ基因已插入痘苗病毒基因组内预期的ＴＫ区段，间接免疫荧光检测显示，重组病毒感染细胞后能有效地表达ＨＳＶ－２ｇＤ蛋白。     

Glycoprotein gB of herpes simplex virus expresses type-common and type-specific antigenic determinants in vivo.

Four monoclonal antibodies directed against glycoprotein B of herpes simplex virus were evaluated for their ability to immunize mice passively against acute virus-induced neurological illness and death when administered intraperitoneally 2 hours prior to footpad challenge with type 1 or type 2 virus. Two monoclonal antibodies, H120 and H157, failed to reduce the severity of neurological disease in infected animals. In contrast, H233 and H368 antibodies provided significant protection in type-common and type-specific fashions, respectively. A direct correlation was observed between in vitro neutralization and in vivo protection. These results provide the first in vivo evidence that glycoprotein gB of herpes simplex virus expresses both type-common and type-specific determinants during the evolution of acute virus-induced neurological disease.     

Induction of bilateral retinal necrosis in mice by unilateral intracameral inoculation of a glycoprotein-C deficient clinical isolate of herpes simplex virus type 1

Summary Herpes simplex virus can cause acute retinal necrosis, a blinding retinal disease in man. A unilateral intracameral inoculation of herpes simplex virus type 1 (HSV-1) in mice induces retinal necrosis primarily in the contralateral eye and provides an experimental model for the disease. Previous studies suggested that a major envelope glycoprotein of HSV-1, glycoprotein C (gC), is required for retinal necrosis. We studied HSV-1 strain TN-1, a gC-deficient clinical isolate from a lesion of herpetic keratitis, for its pathogenicity in mice with an intracameral inoculation of the virus and found that TN-1 could induce severe necrotizing retinitis in both inoculated and uninoculated eyes of BALB/c mice. Inoculation with a lower dose of TN-1 resulted in a unilateral necrotizing retinitis in the uninoculated eyes. Tissue virus titration of infected mice killed at various times after inoculation detected an infectious virus in various organs including the eyeballs, trigeminal ganglia, brain and adrenal glands. Anterior chamber-associated immune deviation (ACAID) was observed in TN-1-inoculated mice as well as in mice inoculated with gC-positive laboratory strain KOS 7 days postinoculation. Our findings suggested that gC of HSV-1 is not necessary for either the induction of retinal necrosis, neural spread of the virus, or ACAID.     

The immunoglobulin response to individual HSV-1 viral polypeptides: kinetics of the response during primary and secondary experimental infection with herpes simplex virus

We studied the immunoglobulin response to individual viral polypeptides in experimental primary and secondary infection with herpes simplex virus (HSV)-1 in mice. After a single footpad inoculation with 10(5.6) pfu of HSV-1, immunoglobulin to proteins mol. wts (10(3)) 44 and 75 appeared on day 7. Antibodies to gB, gC, gD, 42 x 10(3)- and (48-52) x 10(3)-mol. wt proteins appeared on day 11 and antibody to the major capsid protein, VP154, appeared on day 15 after infection. The secondary immune response was characterised by early production of antibody to gD on day 3 followed by antibodies against the 42 x 10(3)- and 44 x 10(3)-mol. wt proteins on days 4 and 5 respectively. Antibodies to glycoprotein gC and gB were delayed until day 7 of the secondary immune response. In both primary and secondary immune responses the responses against proteins of mol. wts (10(3)) 42 and 44 were particularly intense and of high titre. We conclude that the kinetics of anti-polypeptide antibody appearance is markedly asynchronous; and that the anti-glycoprotein responses occur too late in primary infection to contribute to viral clearance.     

Efficacy of herpes simplex virus type 1 immunization in protecting against acute and latent infection by herpes simplex virus type 2 in mice.

ICR mice were immunized with herpes simplex virus type 1 (HSV-1) and later challenged with HSV-2 by footpad inoculation. Both immunized animals and age-matched, nonimmunized controls were observed for ascending neurological disease and latent infection of spinal ganglia resulting from the HSV-2 challenge. Control animals had a 78% incidence of acute and latent infection compared with a 1.7% incidence in immunized mice. The data show immunity to HSV-1 is protective against both acute and latent infection by HSV-2.     

Analysis of the intracellular maturation of the herpes simplex virus type 1 glycoprotein gH in infected and transfected cells.

We have expressed the HSV-1 glycoprotein, gH, in transiently transfected COS-1 cells. The expressed protein was retained intracellularly, contained unprocessed carbohydrate, and was unrecognized by the monoclonal antibody, LP11. In addition, the protein was aggregated. These properties suggest that unlike other HSV glycoproteins, gH is misfolded in transfected cells. Pulse-chase studies of HSV-1-infected cells indicate that the kinetics of processing of gH are comparable to those of gB, gC, and gD. Rescue studies suggest that gH may interact with another protein during maturation in infected cells. However, we were unable to detect any stable interaction, although analysis of gH on neutral sucrose gradients shortly after synthesis indicated a possible transient association with a high molecular weight molecule or complex. The processing and cell surface expression of gH were also analyzed in HSV-1 virus mutants lacking gB, gC, or gD. Our results indicate that the maturation and cell surface transport of gH did not require the presence of these HSV-1 glycoproteins. In addition, three truncation mutants were constructed by linker insertion mutagenesis. Each of the three truncated proteins was synthesized, but the proteins were aggregated, contained only endo H-sensitive carbohydrate, and none were secreted.     

Necrotizing chorioretinitis in mice inoculated with herpes simplex virus type 1 with or without glycoprotein C: anterior chamber-associated immune deviation does not persist

Summary BALB/c mice developed contralateral necrotizing retinitis following intracameral inoculation with herpes simplex virus type 1 (HSV-1). The animals showed a positive delayed-type hypersensitivity (DTH) response at 10 days postinoculation, indicating that the anterior chamber-associated immune deviation was transient after HSV-1 inoculation. Since glycoprotein C (gC) of HSV-1 is a major immunogen, we examined DTH and the antibody response induced by a gC-deficient strain TN-1 and compared them with those induced by the recombinant gC-positive mutants. We found that gC was not required for DTH reaction, and that gC was neither necessary for nor protective against the contralateral retinal necrosis. Serial lymphocyte subset analyses of the draining lymph nodes revealed an absolute increase of B cells, CD 4-positive T cells, and CD 8-positive T cells. CD 4-positive T cells but not CD 8-positive T cells increased in the contralateral eyes during the inflammation and necrosis. The coincident emergence of the positive DTH and contralateral retinal necrosis of HSV-1-inoculated mice, together with the presence of CD 4-positive cells in the retina, indicated that CD 4-positive T cells responsible for DTH induction may participate in the retinal necrosis.     

Protective immunity against lethal HSV-1 challenge in mice by nucleic acid-based immunisation with herpes simplex virus type-1 genes specifying glycoproteins gB and gD

DNA-based vaccines were employed to assess protective immunity against herpes simplex virus in experimental infections of hairless (strain SKH1) and BALB/c mice. Mice were vaccinated with plasmids containing the herpes simplex virus type-1 (HSV-1) glycoprotein B (gB) or D (gD) genes under the human cytomegalovirus immediate-early promoter control. Vaccines were injected intramuscularly (i.m.) or intraperitoneally (i.p.) as purified DNA alone or as formulations supplemented with different non-ionic block copolymers. Antibody responses were assessed by immunofluorescence and radio-immunoprecipitation assays. Mice inoculated with either gB or gD plasmid, alone or with non-ionic block copolymers CRL 1029 and CRL 1190, produced high levels of antibodies specific for gB or gD. Three weeks after the last vaccination, mice were challenged with a clinical HSV-1 isolate (ABGK-1) by inoculation of a shaved and subsequently scarified area between the third and fourth lumbar vertebrae. Mice immunised with either gD or gB plasmid alone or mixed with copolymers were protected against lethal HSV-1 challenge when immunisation was performed via the i.m. route. Immunisations given via the i.p. route induced humoral responses in some mice and protected the animals against lethal HSV-1 challenge only when the formulations contained copolymers. The BALB/c mouse model was shown to be as good a model as the hairless mouse model.     

Identification and preliminary mapping with monoclonal antibodies of a herpes simplex virus 2 glycoprotein lacking a known type 1 counterpart

The properties of herpes simplex virus 2 (HSV-2)-specific proteins reactive with monoclonal antibody H966 derived from mice immunized with HSV-2 strain G are reported. The reactive proteins contained in infected cell lysates subjected to electrophoresis in denaturing gels and transferred to nitrocellulose sheets form a relatively sharp band characteristic of Mr 124,000 proteins and a diffuse, more slowly migrating band. Antigens reactive with H966 were detected on the surface of viable, unfixed cells. The electrophoretic mobility of the H966-reactive proteins made in the presence of tunicamycin was more rapid than that of the proteins made in the absence of the drug. Direct evidence that the HSV-2-specific antigen was a glycoprotein emerged from purification of [14C]glucosamine-labeled proteins with similar electrophoretic mobilities by immunoabsorption to H966 bound to Sepharose beads. Analyses of the reactivity of HSV-1 X HSV-2 recombinants indicated the gene specifying the glycoprotein maps in the S component of the DNA. The glycoprotein detected by H966 has no known counterpart in HSV-1 and corresponds to the glycoprotein previously designated as gC of HSV-2 and reported to map to the right of gC specified by HSV-1. Inasmuch as an HSV-2 gene colinear with HSV-1 gC has been reported to specify a glycoprotein currently designated as gC of HSV-2 by Para et al. [J. Virol. 45, 1223-1227 (1983)], the glycoprotein identified by H966 should be designated as gG.     

Kinetic analysis of glycoprotein C of herpes simplex virus types 1 and 2 binding to heparin,heparan sulfate,and complement component C3b

Glycoprotein C (gC) from herpes simplex virus (HSV) facilitates virus entry by attaching the virion to host cell-surface heparan sulfate (HS). Although gC from HSV-1 (gC1) and from HSV-2 (gC2) bind to heparin, gC2 is believed to play a less significant role than gC1 in attachment of virus to cells. This attachment step is followed by the binding of gD to one of several cellular receptors. gC also plays an important role in immune evasion by binding to the C3b fragment of the third component of the host complement system. Yet, although both gC1 and gC2 protect HSV against complement-mediated neutralization, only gC on HSV-1-infected cells acts as a receptor for C3b. We used optical biosensor technology to quantitate the affinities (K(D)) and the stabilities (k(off)) between both serotypes of gC with heparin, HS, and C3b to address three questions concerning gC interactions. First, can differences in affinity or stability account for differences between the contributions of HSV-1 and HSV-2 gC in attachment? Our data show that the gC2-HS complex is highly unstable (k(off) = 0.2 s(-1)) compared to the gC1-HS complex (k(off) = 0.003 s(-1)), suggesting why gC2 may not play an important role in attachment of virus to cells as does gC1. Second, does gC2 have a lower affinity for C3b than does gC1, thereby explaining the lack of C3b-receptor activity on HSV-2 infected cells? Surprisingly, gC2 had a 10-fold higher affinity for C3b compared to gC1, so this functional difference in serotypes cannot be accounted for by affinity. Third, do differences in gC-HS and gD-receptor affinities support a model of HSV entry in which the gC-HS interaction is of lower affinity than the gD-receptor interaction? Our biosensor results indicate that gC has a higher affinity for HS than gD does for cellular receptors HveA (HVEM) and HveC (nectin-1).     

A block in glycoprotein processing correlates with small plaque morphology and virion targetting to cell-cell junctions for an oral and an anal strain of herpes simplex virus type-1

Summary The characteristics of two clinical isolates of HSV-1 obtained from an oral (424) and an anal (490) lesion were compared with the highly passaged KOS strain. In contrast to KOS, the clinical isolates produced small plaques, were more cell-associated and the predominant viral glycoprotein species for gC and gD in infected cell lysates was the precursor, high mannose glycoform. Total virus production in Vero cells was equivalent for the three virus strains in one-step growths. Pulse-chase studies of glycoprotein C processing showed a reduction in rate at 7.5h post infection and a significant block in processing at 10.5h post infection for 424 and 490 but not KOS. Similar results were obtained for gD. The significant reduction in glycoprotein processing for 424 and 490 suggests a block in transport of viral glycoproteins or virions to and through the Golgi apparatus. Extracellular virions and the cell surface, prior to cell lysis, contained the processed gC glycoform suggesting a competent cellular glycan processing system. Upon co-infection of 424 or 490 with KOS or a gC^– KOS strain, gC was processed to levels equivalent to KOS indicating that 424 and 490 are not inhibitory but that an activity(s) encoded by KOS facilitates maturation of gC from 424 and 490. Unlike KOS infected Vero cells, virion-containing vacuoles were observed in the cytoplasm at 12h p.i. and extracellular virions were concentrated at cell-cell junctions of 424 or 490 infected cells but not in the perinuclear region. These results suggest that intracellular transport of viral glycoproteins and virions in 424 and 490 infected cells is different from KOS infected cells. The reduced level of viral glycoprotein maturation, virus release, cell surface presence and presence of virions at cell-cell junctions are consistent with small plaque production in tissue culture cells.Portions of this work were presented in the 17th International Herpesvirus Workshop, Pittsburgh, PA, 1993.     

DNA immunization with a herpes simplex virus 2 bacterial artificial chromosome

Construction of a herpes simplex virus 2 (HSV-2) bacterial artificial chromosome (BAC) is described. BAC vector sequences were inserted into the thymidine kinase gene of HSV-2 by homologous recombination. DNA from cells infected with the resulting recombinant virus was transformed into E. coli, and colonies containing the HSV-2 BAC (HSV2-BAC) were isolated and analyzed for the expected genotype. HSV2-BAC DNA was infectious when transfected back into mammalian cells and the resulting virus was thymidine kinase negative. When used to immunize mice, the HSV2-BAC DNA elicited a strong HSV-2 specific antibody response that was equal to or greater than live virus immunization. Further, HSV2-BAC immunization was protective when animals were challenged with a lethal dose of virus. The utility of the HSV2-BAC for construction of recombinant virus genomes was demonstrated by elimination of the HSV-2 glycoprotein D (gD) gene. A recombinant HSV-2 BAC with the gD gene deleted was isolated and shown to be incapable of producing infectious virus following transfection unless an HSV gD gene was expressed in a complementing cell line. Immunization of mice with the HSV2 gD-BAC also elicited an HSV-2 specific antibody response and was protective. The results demonstrate the feasibility of DNA immunization with HSV-2 bacterial artificial chromosomes for replicating and nonreplicating candidate HSV-2 vaccines, as well as the utility of BAC technology for construction and maintenance of novel HSV-2 vaccines. The results further suggest that such technology will be a powerful tool for dissecting the immune response to HSV-2.     

Cell-mediated immunity to herpes simplex virus: recognition of type-specific and type-common surface antigens by cytotoxic T cell populations.

In this communication, we examine the specificity of anti-herpes simplex virus (HSV) cytotoxic T lymphocytes (CTL). Serological studies of the two related HSV serotypes (HSV-1 and HSV-2) have revealed both type-specific and cross-reactive antigenic determinants in the viral envelope and on the surface of infected cells. By analysis of cytotoxicity of CTL, generated in vitro by restimulation of splenocytes from mice primed with one or the other HSV serotype, the recognition of both type-specific and cross-reactive determinants on infected target cells by anti-HSV CTL was detectable. Thus, effector cells generated by priming and restimulating with the same virus recognized both type-specific and cross-reactive determinants on target cells infected with the homologous virus, but only cross-reactive determinants on target cells infected with the heterologous HSV serotype. CTL generated by restimulation with the heterologous virus were capable of recognizing only the cross-reactive determinants on either HSV-1- or HSV-2-infected target cells. These results indicate that two subpopulations of CTL exist in a population of anti-HSV immune spleen cells--those which recognize type-specific determinants and those specific for cross-reactive antigenic determinants present on the surface of HSV infected cells. The type-specific subset of anti-HSV CTL was shown to recognize the gC glycoprotein of HSV-1 infected target cells. In addition to the gC glycoprotein, at least one other type-specific surface antigen was also recognized by anti-HSV CTL in addition to the cross-reactive determinants recognized by anti-HSV CTL.     

Vaginal infection of mice with HSV type 2 variant ER-: a new animal model for human primary genital HSV type 2 infections.

Studying the pathogenesis of vaginal infections in mice with two variants of Herpes simplex virus type 2 (HSV-2) strain ER we observed that both variants ER+ and ER- caused severe vaginitis but only ER+ invaded the CNS leading to lethal neurological disease. In contrast, mice infected with ER- cleared the virus from the vagina and recovered from infection. ER+ and ER- expressed equal levels of thymidine kinase (TK) indicating a TK-independent difference in neurovirulence. Using the non-neurovirulent variant ER-, we were able to investigate humoral immune responses later after infection. Vaginal infection with ER- suppressed serum antibody formation after a secondary systemic HSV-1 infection. Fresh isolates of HSV-1 and HSV-2 caused uniformly a lethal neurological disease after vaginal inoculation of mice. However, some animals survived an intraperitoneal infection with these isolates. Infection with HSV-1 isolates stimulated a strong antibody production, whereas infection with HSV-2 isolates suppressed antibody formation, thus supporting earlier results from our group obtained with laboratory strains. Since suppression of antibody formation could be demonstrated with clinical HSV-2 isolates and likewise after vaginal infection with HSV-2 variant ER- we consider this phenomenon to be of relevance in human genital HSV-2 infections. Vaginal infection of mice with variant ER- represents a new model for primary genital HSV-2 infections; this model could be useful for histopathological, virological, immunological and drug testing studies.