Nondetectable levels of interferon gamma is a critical host defense during the first day of herpes simplex virus infection

The inflammatory response triggered by Influenza virus: a two edged sword

Influenza A virus (IAV) is a relevant respiratory tract pathogen leading to a great number of deaths and hospitalizations worldwide. Secondary bacterial infections are a very common cause of IAV associated morbidity and mortality. The robust inflammatory response that follows infection is important for the control of virus proliferation but is also associated with lung damage, morbidity and death. The role of the different components of immune response underlying protection or disease during IAV infection is not completely elucidated. Overall, in the context of IAV infection, inflammation is a 'double edge sword' necessary to control infection but causing disease. Therefore, a growing number of studies suggest that immunomodulatory strategies may improve disease outcome without affecting the ability of the host to deal with infection. This review summarizes recent aspects of the inflammatory responses triggered by IAV that are preferentially involved in causing severe pulmonary disease and the anti-inflammatory strategies that have been suggested to treat influenza induced immunopathology.

Vaccine-induced T cell-mediated immunity plays a critical role in early protection against pseudorabies virus (suid herpes virus type 1) infection in pigs

The aim of our study was to evaluate the relative importance of antibody and T cell-mediated immunity in protection against pseudorabies virus (suid herpes virus type 1) infection in pigs. We induced different levels of immune responses by using: (1) a modified live vaccine; (2) the same modified live vaccine with an oil-in-water (o/w) adjuvant; (3) an inactivated vaccine; and (4) the same inactivated vaccine with an o/w adjuvant. Subsequently, we challenged pigs with virulent pseudorabies virus (PRV). We demonstrated that best-protected pigs stood out by maintaining strong T cell-mediated immune (CMI) responses after challenge. Of the immune parameters tested, protection against virus shedding was correlated best with the magnitude of the IFN-gamma response of in vitro re-stimulated peripheral blood mononuclear cells (PBMC) with an additional role for PRV-specific IgG2 antibodies. The use of an o/w adjuvant resulted in higher antibody and CMI responses, in particular with an increased frequency of memory T helper blast cells of in vitro re-stimulated PBMC. However, this adjuvant-induced enhancement of the immune response had a limited additional effect on the efficacy of inactivated vaccines. This study suggests a major contribution of the CMI response in early protection against PRV infection and that PRV-induced IFN-gamma responses may serve as a suitable indicator for assessing the immune status of vaccinated pigs.

Cytokine expression in murine corneas during recurrent herpetic stromal keratitis

PURPOSE

Recurrent herpetic stromal keratitis (HSK) is a potentially blinding, immune-mediated disease. To better understand the immunopathology of recurrent HSK, we examined the cytokine profile of mouse corneas with the condition.

METHODS

The eyes of latently infected mice were examined for corneal pathology and cytokine content following UV-B-stimulated herpes simplex virus (HSV) reactivation.

RESULTS

Peak HSV-induced corneal disease, manifested by stromal opacification, occurred 7-14 days after viral reactivation in latently infected mice. In qualitative RT-PCR analyses, IFNgamma, IL-10, IL-4, and IL-12 p40 mRNA were simultaneously expressed before and during recurrent HSK. Competitive, semi-quantitative RT-PCR evaluation of cytokine mRNA revealed highest IFNgamma expression before and during clinical disease with a decline thereafter. IL-4 levels peaked and declined before day 14, while IL-10 peaked on days 7 or 14 and paralleled IFNgamma at lower levels. Small amounts of IL-12 p40 mRNA were detected late in the disease course. ELISA evaluation of corneal extracts demonstrated similar results, featuring early expression of Th2 cytokines relative to disease.

CONCLUSIONS

The presence of Th2 cytokines during early stages of recurrent herpetic corneal lesions indicate the presence of a mixed Th1 and Th2 cell infiltrate, which is likely associated with a memory response to viral antigens. These data suggest that disease resolution in corneas with recurrent HSK may depend upon the balance between destructive and protective cytokines at individual sites of viral recurrence.

Role of interleukin-4 (IL-4), IL-12, and gamma interferon in primary and vaccine-primed immune responses to Friend retrovirus infection

The immunological resistance of a host to viral infections may be strongly influenced by cytokines such as interleukin-12 (IL-12) and gamma interferon (IFN-gamma), which promote T helper type 1 responses, and IL-4, which promotes T helper type 2 responses. We studied the role of these cytokines during primary and secondary immune responses against Friend retrovirus infections in mice. IL-4- and IL-12-deficient mice were comparable to wild-type B6 mice in the ability to control acute and persistent Friend virus infections. In contrast, more than one-third of the IFN-gamma-deficient mice were unable to maintain long-term control of Friend virus and developed gross splenomegaly with high virus loads. Immunization with a live attenuated vaccine virus prior to challenge protected all three types of cytokine-deficient mice from viremia and high levels of spleen virus despite the finding that the vaccinated IFN-gamma-deficient mice were unable to class switch from immunoglobulin M (IgM) to IgG virus-neutralizing antibodies. The results indicate that IFN-gamma plays an important role during primary immune responses against Friend virus but is dispensable during vaccine-primed secondary responses.

Gamma interferon is not required for mucosal cytotoxic T-lymphocyte responses or heterosubtypic immunity to influenza A virus infection in mice

Heterosubtypic immunity (HSI) is defined as cross-protection against influenza virus of a different serotype than the virus initially encountered and is thought to be mediated by influenza virus-specific cytotoxic T lymphocytes (CTL). Since gamma interferon (IFN-gamma) stimulates cytotoxic cells, including antigen-specific CTL which may control virus replication by secretion of antiviral cytokines such as tumor necrosis factor alpha and IFN-gamma, we have investigated the mechanism of HSI by analyzing the role of IFN-gamma for HSI in IFN-gamma gene-deleted (IFN-gamma(-/-)) mice. It has been reported that IFN-gamma is not required for recovery from primary infection with influenza virus but is important for HSI. Here, we conclusively show that IFN-gamma is not required for induction of secondary influenza virus-specific CTL responses in mediastinal lymph nodes and HSI to lethal influenza A virus infection. Although T helper 2 (Th2)-type cytokines were upregulated in the lungs of IFN-gamma(-/-) mice after virus challenge, either Th1- or Th2-biased responses could provide heterosubtypic protection. Furthermore, titers of serum-neutralizing and cross-reactive antibodies to conserved nucleoprotein in IFN-gamma(-/-) mice did not differ significantly from those in immunocompetent mice. These results indicate that lack of IFN-gamma does not impair cross-reactive virus-specific immune responses and HSI to lethal infection with influenza virus. Our findings provide new insight for the mechanisms of HSI and should be valuable in the development of protective mucosal vaccines against variant virus strains, such as influenza and human immunodeficiency virus.

A mouse model to study immunity against pseudorabies virus infection: significance of CD4+ and CD8+ cells in protective immunity

In this study we firstly established a vaccination/challenge model to study pseudorabies virus infection in mice. The mouse model was used to investigate the significance of CD4+ and CD8+ cells and of IFN gamma production in protective immunity. Functional depletion of CD4+ and CD8+ and IFN gamma was obtained in vivo by intraperitoneal injection of alginate-encapsulated anti-CD4, -CD8 or -IFN gamma producing hybridoma's before and at the moment of vaccination. The observed protective immunity was correlated with underlying immunologic responses such as PRV-specific DTH reactivity, lymphoproliferation and cytotoxicity. The significance of CD4+ and CD8+ cells and of IFN gamma production was also investigated for these immunological responses by the same in vivo depletion technique. The results demonstrated that protective vaccination of mice, that could be induced by immunization with 10(7) plaque forming units of the avirulent PRV mutant NIA3 TK-, was characterized by a typical anti-viral Th1 type immune response. A clear PRV-specific, CD4-dependent DTH reactivity and a classical CD8-dependent, MHC-restricted cytotoxicity was induced after protective immunization and the humoral immune response had a bias towards PRV-specific IgG2a formation. In vivo treatment with anti-CD8 and anti-IFN gamma demonstrated that the cytotoxic response and humoral IgG2a response, respectively, were strongly reduced, whereas protection against lethal challenge was unaffected. On the other hand anti-CD4 treatment reduced the induced protection so that 30% of the mice died after lethal challenge. The results of our study demonstrated that CD4+, DTH like effector cells are a crucial effector mechanism for protective immunity against PRV.

Protective role of gamma interferon during the recall response to influenza virus

During secondary immune responses to influenza virus, virus-specific T memory cells are a major source of gamma interferon (IFN-gamma). We assessed the contribution of IFN-gamma to heterologous protection against the A/WSN/33 (H1N1) virus of wild-type and IFN-gamma-/- mice previously immunized with the A/HK/68 (H3N2) virus. The IFN-gamma-/- mice displayed significantly reduced survival rates subsequent to a challenge with various doses of the A/WSN/33 virus. This was associated with an impaired ability of the IFN-gamma-/- mice to completely clear the pulmonary virus by day 7 after the challenge, although significant reduction of the virus titers was noted. However, the IFN-gamma-/- mice developed type A influenza virus cross-reactive cytotoxic T lymphocytes (CTLs) similar to the wild-type mice, as demonstrated by both cytotoxicity and a limiting-dilution assay for the estimation of CTL precursor frequency. The pulmonary recruitment of T cells in IFN-gamma-/- mice was not dramatically affected, and the percentage of CD4(+) and CD8(+) T cells was similar to that of wild-type mice. The T cells from IFN-gamma-/- mice did not display a significant switch toward a Th2 profile. Furthermore, the IFN-gamma-/- mice retained the ability to mount significant titers of WSN and HK virus-specific hemagglutination-inhibiting antibodies. Together, these results are consistent with a protective role of IFN-gamma during the heterologous response against influenza virus independently of the generation and local recruitment of cross-reactive CTLs.

Quantitative detection of porcine interferon-gamma in response to mitogen, superantigen and recall viral antigen

Five monoclonal antibodies (mAbs) specific for porcine interferon-gamma (PoIFN-gamma) were isolated and utilized to develop a PoIFN-gamma sandwich ELISA. Specific reactivity of each mAb with E. coli derived recombinant PoIFN-gamma, but not with rPoIL-2 or rPolL-10, was confirmed in an indirect ELISA and in Western blots. Competitive ELISAs showed that mAbs P2A4 and P2C11 bound an epitope which was not recognized by mAbs P2G10, P1B7 or P2F6. The latter three mAbs were able to neutralize the ability of natural and recombinant PoIFN-gamma to induce the de novo expression of class II MHC antigens on porcine endothelial cells. To simplify the detection of biologically active porcine IFN-gamma, a sandwich ELISA was developed using the mAb P2G10 as a capture antibody and mAb P2C11 as the detecting reagent. The sensitivity of the assay for PolFN-gamma ranged from 1 to 50 ng/ml. Peripheral blood mononuclear cells (PBMC) from all pigs tested produced IFN-gamma when stimulated with either mitogen (PHA) or superantigen (SEB). In contrast, only PBMC obtained from pigs which had previously been vaccinated against PrV produced IFN-gamma in response to stimulation with this virus. Interestingly, cultures with the highest lymphoproliferative response did not necessarily have the highest level of IFN-gamma production.Furthermore, for recall viral antigen, the lymphoproliferative response decreased with time after immunization, whereas the IFN-gamma response increased. Thus, measurement of IFN-gamma production appears to be a good indicator of anti-viral immunological memory.

Interferon-gamma and tumor necrosis factor-alpha specifically induce formation of cytomegalovirus-permissive monocyte-derived macrophages that are refractory to the antiviral activity of these cytokines

Monocytes/macrophages are key cells in the pathogenesis of human cytomegalovirus (HCMV). Although HCMV infection in monocytes is restricted to early events of gene expression, productive infection has been demonstrated in differentiated macrophages in vitro. We examined the cellular and cytokine components that are essential for HCMV replication in Concanavalin A-stimulated monocyte-derived macrophages (MDM). By negative selection, depletion of CD8+ T lymphocytes, but not CD4+ T lymphocytes, CD19+ B cells, or CD56+ NK cells, resulted in a 60-70% reduction in the number of HCMV-infected MDM, and a 4 log decrease in virus production. Neutralization of IFN-gamma and TNF-alpha, but not IL-1, IL-2, or TGF-beta, decreased production of virus by 4 logs and 2 logs, respectively. Subsequently, addition of recombinant IFN-gamma or TNF-alpha to purified monocyte cultures was sufficient to produce HCMV-permissive MDM. While IFN-gamma and TNF-alpha possess antiviral properties, addition of these cytokines to permissive MDM cultures did not affect production of HCMV. Thus, rather than inhibiting replication of HCMV, IFN-gamma and TNF-alpha specifically induce differentiation of monocytes into HCMV-permissive MDM, which are resistant to the antiviral effects of these cytokines.

Immunohistological characterization of the local cellular response directed against pseudorabies virus in pigs

The aim of this study was to investigate the kinetics of a primary and secondary immune response against pseudorabies virus (PRV). Pigs vaccinated with strain 783 and unvaccinated pigs were challenged with wild-type PRV by either intranasal or subcutaneous infection. Non-challenged pigs were used as controls. On days 1, 3 and 7 after challenge, tissues from the site of infection, and the tonsils of intranasally and the draining lymph nodes of subcutaneously challenged pigs were sampled. Immunohistological staining was used to characterize the various cell populations at the primary site of virus replication and in the lymphoid tissue. Tissue sections were stained for the T-cell markers CD2, CD3 gamma delta, CD4 and CD8, for the B-cell markers IgM, IgA and IgG, for a macrophage marker, and for PRV antigen. After challenge, PRV was detected during a shorter period in vaccinated pigs, and was less disseminated than in unvaccinated pigs. Cellular infiltrates were detected both in the nasal mucosa and the subcutaneous tissue of both unvaccinated and vaccinated pigs. Cell infiltrates, however, appeared earlier in vaccinated than in unvaccinated pigs, indicating a difference in kinetics of the primary and secondary immune response. The appearance of T-cells preceded the appearance of B-cells, but the proportion of the various subsets did not differ between unvaccinated and vaccinated pigs. These findings suggest that the early immune response in vaccinated pigs may contribute to the rapid clearance of virus at the primary site of infection. In addition, T-cells appear to have a more important role in the clearance of PRV than B-cells.

Involvement of the complement system in the protection of mice from challenge with respiratory syncytial virus Long strain following passive immunization with monoclonal antibody 18A2B2

Passive immunization of mice with 131 micrograms of the non-neutralizing monoclonal antibody (mAb) 18A2B2, directed against the A subgroup epitope of the G glycoprotein of respiratory syncytial virus Long strain (RSV), confers protection against viral i.n. challenge. The role of the Fc fragment of this antibody as well as the involvement of antibody-dependent cellular cytotoxicity (ADCC) and complement-mediated cytolysis towards protection was evaluated in vivo. Passive immunization with the Fab fragment alone (618-907 micrograms mouse-1) was unable to confer protection in mice. Furthermore, we passively immunized with the mAb 18A2B2 SCID beige mice, which are deficient in natural killer (NK) cell activity, to ascertain the role of NK cells in the protective mechanism. These mice were free of virus 5 days following viral challenge, indicating that NK cells do not contribute significantly towards the protective action of this antibody. Moreover, passively immunized BALB/c mice decomplemented with 8-10 U of cobra venom factor (CoVF) and DBA/2J mice (C5 deficient) were only partially protected. These findings suggest that in mice the alternative and classical pathways of the complement system are involved in the passive protection mechanism conferred by the non-neutralizing mAb 18A2B2. To our knowledge, it is the first description of a protective mechanism in mice that involves a non-neutralizing antibody and the complement system.

Gamma interferon expression during acute and latent nervous system infection by herpes simplex virus type 1

This study was initiated to evaluate a role for gamma interferon (IFN-gamma) in herpes simplex virus type 1 (HSV-1) infection. At the acute stage of infection in mice, HSV-1 replication in trigeminal ganglia and brain stem tissue was modestly but consistently enhanced in mice from which IFN-gamma was by ablated monoclonal antibody treatment and in mice genetically lacking the IFN-gamma receptor (Rgko mice). As determined by reverse transcriptase PCR, IFN-gamma and tumor necrosis factor alpha transcripts were present in trigeminal ganglia during both acute and latent HSV-1 infection. CD4+ and CD8+ T cells were detected initially in trigeminal ganglia at day 5 after HSV-1 inoculation, and these cells persisted for 6 months into latency. The T cells were focused around morphologically normal neurons that showed no signs of active infection, but many of which expressed HSV-1 latency-associated transcripts. Secreted IFN-gamma was present up to 6 months into latency in areas of the T-cell infiltration. By 9 months into latency, both the T-cell infiltrate and IFN-gamma expression had cleared, although there remained a slight increase in macrophage levels in trigeminal ganglia. In HSV-1-infected brain stem tissue, T cells and IFN-gamma expression were present at 1 month but were gone by 6 months after infection. Our hypothesis is that the persistence of T cells and the sustained IFN-gamma expression occur in response to an HSV-1 antigen(s) in the nervous system. This hypothesis is consistent with a new model of HSV-1 latency which suggests that limited HSV-1 antigen expression occurs during latency (M. Kosz-Vnenchak, J. Jacobson, D.M. Coen, and D.M. Knipe, J. Virol. 67:5383-5393, 1993). We speculate that prolonged secretion of IFN-gamma during latency may modulate a reactivated HSV-1 infection.

The antiviral activity of tumour necrosis factor on herpes simplex virus type 1: role for a butylated hydroxyanisole sensitive factor

We have previously shown that specific antibodies (Mab 32/Ab 301) against tumour necrosis factor (TNF) enhance its antiviral activity in vaccinia virus-infected mice. In the present study, TNF alone was found to have antiviral activity against herpes simplex virus-1 (HSV-1). Antibody enhancement was found, both in vivo and in vitro, at lower TNF doses. The magnitude of the TNF-induced antiviral response was dependent upon the genetic background of the mouse. C57BL/6 mice were very sensitive to the antiviral activity of TNF, which was inhibited by the free radical scavenger butylated hydroxyanisole (BHA). TNF plus Mab 32 induced a significant antiviral effect in L929 cells which was associated with pronounced CPE. The CPE was largely reversed in the presence of BHA, and furthermore, TNF antiviral activity was significantly reversed in the presence of BHA. Specific inhibitors of nitric oxide synthetase, lipoxygenase or cyclo-oxygenase did not influence either the CPE or growth kinetics of HSV-1, suggesting that neither reactive nitrogen intermediates nor arachidonic acid metabolites were involved in the antiviral mechanism of TNF. This, together with observed increases in Cu/Zn SOD levels in virus infected cells, suggests that reactive oxygen intermediates may have a role in the direct control of HSV-1 growth and that free radicals may play a part in the antiviral activity induced by TNF.

The interferons: a biological system with therapeutic potential in viral infections

Successful medical use of interferon for chronic viral infections is increasingly dependent on understanding the biologic and molecular mechanisms of the interferon system. Interferon (IFN) is one of the body's natural defenses. Production of IFN is a defensive response to foreign components of microbes, tumors and antigens. This IFN response begins with the production of the IFN proteins (alpha, beta and gamma) which then induce antiviral, antimicrobial, antitumor, and immunomodulatory actions. Thus, the initial production or administration of IFN(s) does not protect directly but instead reacts with specific receptors on cell surfaces to activate cytoplasmic transduction signals that then enter the nucleus to stimulate cellular genes encoding a number of effector proteins which lead to the defensive actions. The known molecular, humoral and cellular mechanisms by which these effector proteins exert their antiviral activities are presented. In addition, the pathogenesis of chronic infections is overviewed in the context of the interferon defenses.

Distinction of mouse interferon-alpha subtypes by polymerase chain reaction utilizing consensus primers and type-specific oligonucleotide probes

We have developed a novel method to study the subtype-specific expression of interferon-alpha (IFN-alpha) in the mouse system: we synthesized and used consensus oligonucleotide primers to allow simultaneous polymerase chain reaction (PCR) amplification of multiple murine IFN-alpha gene sequences. In addition, a set of subtype-specific oligomer probes were designed and used to distinguish between IFN-alpha genes that differ by only a few bases. The consensus primers, corresponding to two regions highly conserved among murine IFN-alpha subtypes, were used in reverse transcription and PCR amplification of total cellular RNA, isolated from IFN-gamma-treated murine L-929 cells, to yield a fragment of the anticipated approximately 520-bp size. Southern analysis of the amplified product using an internal consensus oligomer probe confirmed specific amplification of murine IFN-alpha gene(s). Subtype-specific oligonucleotide probes indicate that IFNs-alpha 1, -alpha 2, and -alpha 5 are present following IFN-gamma treatment, whereas IFN-alpha 4 remains virtually absent. Our results indicate that the expression of specific IFN-alpha subtypes may be subject to complex regulation, dependent upon inducing agents and cell types involved, and countless other factors. The procedure described here represents a novel method for studying the subtleties of the murine IFN-alpha mRNA expression.

Suppression of rat cytomegalovirus replication by antibodies against gamma interferon

The role of gamma interferon (IFN-gamma) in the resolution of rat cytomegalovirus (RCMV) infection was investigated. In the spleen, IFN-gamma-producing cells reached maximum numbers on day 7 after infection. Prophylactic treatment with high doses of recombinant rat IFN-gamma exerted antiviral activity in fibroblasts and protected immunosuppressed rats against a lethal RCMV challenge. Remarkably, in immunocompetent rats, neutralization of endogenous IFN-gamma activity significantly reduced the numbers of RCMV antigen-expressing cells in the spleen, the predominant site of viral replication. Moreover, protection of radiation-immunosuppressed infected rats by transferred immune T cells was enhanced by coinjection of IFN-gamma neutralizing antibodies. The observations were paralleled by in vitro findings: low concentrations of IFN-gamma enhanced viral replication in both macrophages and fibroblasts. These data suggest that IFN-gamma can play different and even opposite roles in the regulation of RCMV replication in vivo; T lymphocytes may contribute to the progression of RCMV infection by secreting IFN-gamma.

Synergistic anti-HSV effect of tumor necrosis factor alpha and interferon gamma in human corneal fibroblasts is associated with interferon beta induction

HSV-1 (17) replicated to high titer in human corneal fibroblasts (> 10(8) PFU/10(5) cells) following infection at one PFU per 100 cells. Pretreatment of the cells for 24 h with 50 U/ml recombinant human tumor necrosis factor alpha (TNF-alpha) or 5 IU/ml of human interferon gamma (IFN-gamma) resulted in only modest reduction (2- to 19-fold) in virus yield. However, when the two cytokines were combined the antiviral effect was dramatically increased. There was > 1000-fold reduction in virus titer in 8 of 8 trials. In contrast, the combinations of 50 U/ml TNF-alpha with 5 IU/ml IFN-alpha or IFN-beta did not produce a synergistic effect. The pronounced synergistic antiviral activity of TNF-alpha+IFN-gamma could be demonstrated in fibroblast cultures from different donors, and HSV-2 as well as HSV-1 strains were inhibited. There was no evidence that dual cytokine treatment was toxic for uninfected or HSV-infected cells. Insight into the mechanism responsible for the synergistic effect was provided by the observation that TNF-alpha+IFN-gamma induced IFN-beta. In addition, anti-IFN-beta but not anti-IFN-alpha antibodies could reverse the antiviral effect, and reconstitution with IFN-beta could duplicate the phenomenon. We conclude that the combination of TNF-alpha and IFN-gamma at low concentrations can exert a powerful anti-herpes effect in human corneal fibroblasts which can be chiefly attributed to the induction of IFN-beta.

Antibodies may act synergistically or additively with interferon to inhibit poliovirus

We investigated the protective effects of combinations of interferon-alpha (IFN-alpha) and neutralizing monoclonal antibodies (mAbs) and serum antibodies against poliovirus type 1 (PV-1) in vitro. Our results indicate that the antiviral effects of IFN-alpha and most neutralizing mAbs to PV-1 act synergistically to inhibit PV-1. However, the antiviral effects of IFN-alpha and one type specific mAb to PV-1 were additive. Further, the protective effects observed with combinations of IFN-alpha and rabbit, monkey or human serum containing effects observed with combinations strains Mahoney (Mah) and Sabin (Sab) were similar to those observed with combinations of IFN-alpha and mixtures of mAbs with synergistic and additive activities. Our studies suggest that the antiviral activity of neutralizing antibody acts with the antiviral activity of IFN to inhibit virus infection synergistically or additively and that the different antibody activities are associated with the mechanism of neutralization.

Role of interferon in lethality and lymphoid atrophy induced by Coxsackievirus B3 infection in mice

To assess the importance of interferon (IFN) in the pathology of coxsackievirus B3 (CVB-3) infection, we evaluated both mortality rate and lymphoid involution in young adult BALB/C mice infected with lethal doses of the virus and treated either with anti-IFN antibody or with murine IFN-alpha/beta. Administration of antibody to IFN caused a profound worsening of the pathology and an increase in the mortality rate in infected animals. Treatment with murine IFN exerted a significant ameliorative effect on lethality when administered concomitantly with or soon after virus infection. The extent of this protection was correlated with the plasma levels of exogenous or endogenous IFN at 6 h postinfection, whereas no correlation with IFN titers was found later. The effects of IFN apparently were not directly mediated by antiviral effects, because at the times studied, no relation was found between IFN levels and virus titers, at least in the plasma of the infected animals. Lymphoid atrophy, assessed by measuring spleen weight, was only partially reversed by early IFN treatment. These data suggest that IFN production is critical during the early phases of infection, whereas it does not seem to play a significant protective role at later stages.

An assay for the detection of interferon dependent and interferon independent antibody activities

A spectrophotometric assay is described for the detection of interferon (IFN) dependent antibody (IDA) activity (i.e., antibodies that act with IFN to synergistically inhibit virus infection) and IFN independent antibody (IIA) activity (i.e., antibodies that act additively with IFN to inhibit virus infection). Four neutralizing monoclonal antibodies (mAb) against poliovirus type 1 (PV-1) were tested. Three mAb exhibited IDA activity and one mAb exhibited IIA activity against PV-1 strain Sabin. Concomitantly, the respective IDA and IIA activities were confirmed by a yield reduction assay. Also, the spectrophotometric assay detected IIA activity against PV-1 and IDA activity against PV-2 and PV-3 in human serum. Interestingly, antibody to a synthetic peptide of PV-1 capsid protein VP2 exhibited IIA activity against PV-2 strain MEF. Thus, this assay can facilitate the identification and investigation of IDA and IIA activities. Further, the assay adds economic feasibility to studying the natural occurrence of these antibody activities in the general population and can be useful in assessing the therapeutic potential of vaccine induced and hyperimmune antibodies.

Cytopathogenicity, drug susceptibility, and thymidine kinase activity of a retinovirulent herpes simplex virus type 2

We investigated some of the biological and biochemical characteristics of a neuroinvasive, retinovirulent herpes simplex virus type 2 strain SL (HSV-2[SL]) and compared them with those of a neurovirulent, nonretinovirulent HSV-2 (186). HSV-2(SL) was shown to spread rapidly and produce large syncytium in vitro. HSV-2(SL) and HSV-2(186) were equally susceptible to acyclovir (ACV) and thymine arabinoside (Ara-T). However, HSV-2(SL) was fourfold and 44-fold more susceptible than HSV-2(186) to iododeoxyuridine (IUdR) and bromovinyldeoxyuridine (BVDU), respectively. In addition, cytosolic TK from HSV-2(SL)-infected cells phosphorylated 4, 20, and 23,000 times more IUdR, iododeoxycytidine (IdCyD), and Ara-T than the TK of HSV-2(186), respectively. Further, HSV-2(186) TK did not phosphorylate Ara-T, but HSV-2(186) replication was inhibited by Ara-T. These studies indicate that the retinovirulent HSV-2(SL) has a syn phenotype and a TK with broad substrate activity.

Ocular avirulence of a herpes simplex virus type 1 strain is associated with heightened sensitivity to alpha/beta interferon

BALB/c mice infected on the scarified cornea with herpes simplex virus type 1 strain 35 [HSV-1(35)] rarely developed ocular disease even at challenge doses as high as 10(7) PFU per eye. In contrast, HSV-1(RE) consistently induced stromal keratitis at an inoculum of 2 x 10(4) PFU. The goal of this study was to determine the reason for the difference in virulence between the two HSV strains. Both HSV-1 strains replicated to similar titers in excised corneal "buttons." However, after in vivo infection of the cornea, the growth of strain 35 was evident only during the first 24 h postinfection, whereas the replication of strain RE persisted for at least 4 days. In vitro tests revealed that HSV-1(35) was greater than 10 times more sensitive to alpha/beta interferon (IFN-alpha/beta) than HSV-1(RE). Both strains induced comparable serum levels of IFN after intraperitoneal inoculation. The kinetics of HSV-1(35) clearance from the eye was markedly altered by treatment with rabbit anti-IFN-alpha/beta. Virus titers exceeding 10(4) PFU per eye could be demonstrated 4 to 5 days postinfection in mice given a single inoculation of antiserum 1 h after infection. Furthermore, anti-IFN treatment in 3-week-old mice infected with HSV-1(35) led to the development of clinically apparent corneal disease which subsequently progressed to stromal keratitis in the majority of recipients. These results indicate that the striking difference in the capacity of HSV-1(35) and HSV-1(RE) to induce corneal disease was related to the inherently greater sensitivity of strain 35 to IFN-alpha/beta produced by the host in response to infection.

Isolation of a herpes simplex virus type 2 that is retinovirulent in mice

The virulence of a herpes simplex virus type 2 (HSV-2) isolated from the urine of a patient (SL) with acquired immunodeficiency syndrome (AIDS) and bilateral acute retinal necrosis (ARN), was investigated in mice. The ratio of plaque forming units (PFU) in fibroblasts to the 50% lethal dose (LD50) of HSV-2(SL) in mice was 10 fold more than the PFU to LD50 ratio of a neurovirulent HSV-2, strain 186. Further, HSV-2(SL) caused retinitis with and without lethal encephalitis in mice inoculated intracranially (i.c.). In contrast, mice inoculated with HSV-2(186) died of encephalitis without ocular disease. HSV-2(SL) was isolated from eye and/or brain tissue 1 to 15 days post i.c. inoculation. Ocular disease progressed from an initial mild chorioretinitis on day 8 to total retinal necrosis with panuveitis by day 11 in mice given 10 PFU of HSV-2(SL) i.c. HSV antigen was detected initially in the cells of the optic nerve and spread into the ganglial cells of the nerve fiber layer, the neurosensory cells of the inner nuclear layer, and the cells of the retinal pigment epithelium (RPE) between days 8 and 10. Thus, this study supports the concept that HSV neurovirulence varies between strains and presents a HSV-2 neurotransmission animal model of ARN.

Role of interferon-gamma in inducing cytotoxicity of peripheral blood mononuclear leukocytes to bovine herpesvirus type 1 (BHV-1)-infected cells

In the present study, the possible role of interferon (IFN)-gamma on the induction of cytotoxic activity of peripheral blood mononuclear leukocytes (PBML) from BHV-1-immune cattle was investigated. Supernatants obtained from BHV-1-immune PBML, stimulated under conditions similar to those required to demonstrate cytotoxicity, contained an antiviral substance capable of inducing 2'-5'-oligoadenylate synthetase activity in MDBK cells and MHC class II antigen expression on epithelial cells. These supernatants also contained IFN-alpha, but were devoid of tumor necrosis factor and interleukin-2 biological activities. Further studies during primary infection and hyperimmunization with BHV-1 showed that IFN-gamma production and non-MHC-restricted cytotoxicity against BHV-1-infected targets always occurred concomitantly, suggesting that they represent an important part of the detectable CMI responses mounted against this virus. Furthermore, it was also demonstrated that cytotoxicity of PBML against BHV-1-infected cells was reduced with the addition of antibodies to bovine IFN-gamma to the cytotoxic assay. Bovine recombinant IFN-gamma was able to enhance the in vitro cytotoxic activity of PBML from immune cattle, but not from their nonimmune counterparts. This suggests that other factors, in addition to IFN-gamma, may be essential in the development of non-MHC-restricted cytotoxic responses during BHV-1 infection.

Evidence that NK cells and interferon are required for genetic resistance to lethal infection with ectromelia virus

C 57 BL/6 mice developed resistance to lethal intravenous challenge with virulent (Moscow strain) ectromelia virus between 2 and 3 weeks of age. The fraction of C57 BL/6 mice in which virus was detected in spleen was significantly lower than for DBA/2 mice by day 3. Thereafter, C 57 BL/6 mice had significantly reduced virus titers in spleen compared with those of DBA/2 mice. Resistance was abrogated by treatment with anti-asialo GM1 gammaglobulin, which blocks NK cell activity, or with anti-interferon (IFN) alpha, beta. C 57 BL/6 mice carrying the bg/bg mutation, associated with a deficiency of NK cells, were highly susceptible to lethal infection as were athymic mice derived from a resistant genetic background. Virus titers in spleens of C 57 BL/6 mice treated with anti-asialo GM1 or anti-IFN alpha, beta were significantly higher 4 days after virus challenge than were titers in C 57 BL/6 mice treated with normal rabbit serum. The results strongly suggest that genetic resistance to lethal ectromelia virus infection requires non-specific host defenses such as NK cells and IFN alpha, beta that are activated during the first 3 to 4 days of infection.