Vaccine-Associated Maintenance of Epithelial Integrity Correlated With Protection Against Virus Entry

To identify the mechanisms by which human immunodeficiency virus type 1 (HIV-1) might penetrate the epithelial barrier during sexual transmission to women and the mechanisms of vaccine-associated protection against entry, we characterized early epithelial responses to vaginal inoculation of simian immunodeficiency virus strain mac251 (SIVmac251) in naive or SIVmac239Δnef-vaccinated rhesus macaques. Vaginal inoculation induced an early stress response in the cervicovaginal epithelium, which was associated with impaired epithelial integrity, damaged barrier function, and virus and bacterial translocation. In vaccinated animals, early stress responses were suppressed, and the maintenance of epithelial barrier integrity correlated with prevention of virus entry. These vaccine-protective effects were associated with a previously described mucosal system for locally producing and concentrating trimeric gp41 antibodies at the mucosal interface and with formation of SIV-specific immune complexes that block the stress responses via binding to the epithelial receptor FCGR2B and subsequent inhibitory signaling. Thus, blocking virus entry may be one protective mechanism by which locally concentrated non-neutralizing Ab might prevent HIV sexual transmission to women.

Vaccine-modified NF-kB and GR signaling in cervicovaginal epithelium correlates with protection

Cervicovaginal epithelium plays a critical role in determining the outcome of virus transmission in the female reproductive tract (FRT) by initiating or suppressing transmission-facilitating mucosal immune responses in naïve and SIVmac239Δnef-vaccinated animals, respectively. In this study, we examined the very early responses of cervical epithelium within 24 h after vaginal exposure to SIV in naive and SIVmac239Δnef-vaccinated rhesus macaques. Using both ex vivo and in vivo experimental systems, we found that vaginal exposure to SIV rapidly induces a broad spectrum of pro-inflammatory responses in the epithelium associated with a reciprocal regulation of NF-kB and glucocorticoid receptor (GR) signaling pathways. Conversely, maintenance of high-level GR expression and suppression of NF-kB expression in the epithelium were associated with an immunologically quiescent state in the FRT mucosa and protection against vaginal challenge in SIVmac239Δnef-vaccinated animals. We show that the immunologically quiescent state is induced by FCGR2B-immune complexes interactions that modify the reciprocal regulation of NF-kB and GR signaling pathways. Our results suggest that targeting the balance of NF-kB and GR signaling in early cervicovaginal epithelium responses could moderate mucosal inflammation and target cell availability after vaginal infection, thereby providing a complementary approach to current prevention strategies.

Epithelium-innate immune cell axis in mucosal responses to SIV

In the SIV (simian immunodeficiency virus)-rhesus macaque model of HIV-1 (human immunodeficiency virus type I) transmission to women, one hallmark of the mucosal response to exposure to high doses of SIV is CD4 T-cell recruitment that fuels local virus expansion in early infection. In this study, we systematically analyzed the cellular events and chemoattractant profiles in cervical tissues that precede CD4 T-cell recruitment. We show that vaginal exposure to the SIV inoculum rapidly induces chemokine expression in cervical epithelium including CCL3, CCL20, and CXCL8. The chemokine expression is associated with early recruitment of macrophages and plasmacytoid dendritic cells that are co-clustered underneath the cervical epithelium. Production of chemokines CCL3 and CXCL8 by these cells in turn generates a chemokine gradient that is spatially correlated with the recruitment of CD4 T cells. We further show that the protection of SIVmac239Δnef vaccination against vaginal challenge is correlated with the absence of this epithelium-innate immune cell-CD4 T-cell axis response in the cervical mucosa. Our results reveal a critical role for cervical epithelium in initiating early mucosal responses to vaginal infection, highlight an important role for macrophages in target cell recruitment, and provide further evidence of a paradoxical dampening effect of a protective vaccine on these early mucosal responses.

Amino acid phosphoramidate monoesters of 3'-azido-3'-deoxythymidine: relationship between antiviral potency and intracellular metabolism

A series of phosphoramidate monoesters of 3'-azido-3'-deoxythymidine (AZT) bearing aliphatic amino acid methyl esters (3a, 3c, 4a, 4c, 5-7) and methyl amides (3b, 3d, 4b, 4d) was prepared and evaluated for anti-HIV-1 activity in peripheral blood mononuclear cells (PBMCs). These compounds, which showed no cytotoxicity at concentrations of 100 microM, were effective at inhibiting HIV-1 replication at concentrations of 0.08-30 microM. Since the D-phenylalanine and D-tryptophan derivatives exhibited equivalent or enhanced antiviral activity compared to their L-counterparts, there appears to be no specific stereochemical requirement for the amino acid side chain. In addition, except for the D-phenylalanine derivatives, the methyl amides had greater antiviral activity than the corresponding methyl esters. On the basis of the observed antiviral activity of AZT phosphoramidate monoesters 3a and 4a in PBMCs and CEM cells, the mechanism of action of these two compounds was investigated. AZT-MP and substantial amounts of either phosphoramidate were detected in PBMCs and CEM cells treated with either 3a or 4a. Biological mechanistic studies demonstrated that 3a and 4a affect viral replication at a stage after virus entry and preceding viral DNA integration. Quantitation of the intracellular levels of AZT-TP in PBMCs and CEM cells treated with 3a and 4a in the presence and absence of exogenous thymidine correlated the intracellular levels of AZT-TP to the antiviral activity and suggested that AZT-TP was responsible for the activity observed. In addition, the reduced toxicity of 3a and 4a toward CEM cells relative to AZT correlated with reduced levels of total phosphorylated AZT and not AZT-TP. Stable carbamate analogues of 3a and 4a were prepared and shown to inhibit the production of AZT-MP from cell-free extracts of CEM cells, further suggesting that a phosphoramidate hydrolase may be responsible for intracellular P-N bond cleavage. Taken together, these results suggest that the biological activity and intracellular metabolism of nucleoside phosphoramidate monoesters are distinct from that of phosphoramidate diesters.

Clinicopathological studies of a patient with adult T-cell leukemia and pseudogynecomasty

We present a rare case of adult T cell leukemia/lymphoma (ATL) in which leukemic T cells expressed CD4 and CD25 surface antigens and infiltrated mammary glands during clinical course of the disease. A 40-year-old male was admitted with long-standing skin lesions and leukocytosis. Peripheral blood lymphocytes were highly pleomorphic and presented CD2, CD4, CD25, CD38 membrane surface antigens. The patient proved to be seropositive for human T-cell lymphotropic virus type I (HTLV-I) antibodies. Monoclonal expansion of lymphoid cells integrated with HTLV-I genome was observed, and the diagnosis of ATL chronic type was made. He underwent a chemotherapy regimen, and skin lesions and leukocytosis improved markedly. He progressed with an indolent clinical course of ATL, when he was admitted with bilateral hyperplasia of breast, recurrent skin lesions, and leukocytosis. Breast biopsy revealed bilateral gynecomasty, extensive leukemic infiltration of typical ATL cells in the mammary glands, and the presence of mammary epithelial cells productively infected with HTLV-I. This is the first report describing invasion of the mammary tissue with HTLV-I-transformed T-cells and HTLV-I-associated breast disease.

A nonpeptide integrin antagonist can inhibit epithelial cell ingestion of Streptococcus pyogenes by blocking formation of integrin alpha 5beta 1-fibronectin-M1 protein complexes

Streptococcus pyogenes can be efficiently internalized by a variety of human epithelial cells. beta-lactam antibiotics, commonly used to treat S. pyogenes infections, do not readily permeate mammalian cells. There is growing evidence that the ability of streptococci to enter host cells contributes to the frequent failure of antibiotics to eradicate the organism from infected individuals. Recent studies have suggested that host cell entry requires the formation of a complex of a bacterial fibronectin (Fn) binding protein (e.g., M1 protein or protein F1/SfbI), human Fn, and the epithelial cell Fn receptor, integrin alpha5beta1. We report here that a low molecular weight, nonpeptide antagonist of integrin alpha5beta1, SJ755, can inhibit internalization of streptococci by primary human tonsillar epithelial cells and immortalized human epithelial (A549) cells, thus increasing the extent of bacterial killing by antibiotics. SJ755 blocked Fn binding by human tonsillar epithelial and A549 cells, suggesting that integrin alpha5beta1 is the major Fn receptor expressed by both cell types. SJ755 did not affect Fn binding by purified M1 protein or M1(+) bacteria. Purified M1 protein failed to associate with integrin alpha5beta1 unless the integrin had been prebound by Fn. Also, SJ755 blocked formation of alpha5beta1-Fn-M1 complexes in vitro. These results support the previous proposal that Fn functions as a molecular bridge between M1 protein and integrin alpha5beta1. Furthermore, these results suggest that integrin antagonists may enhance the efficacy of antibiotics in treatment of S. pyogenes infections.

Mammary epithelial cells support and transfer productive human T-cell lymphotropic virus infections

OBJECTIVES

To investigate whether luminal and basal human mammary epithelial cells (HMEC) are susceptible to productive infection by human T-cell lymphotropic virus types I and II (HTLV-I and HTLV-II) and whether HTLV infection of breast epithelial cells could contribute to the seeding of milk with HTLV infectivity and support virus transmission from mother to nursing infant.

STUDY DESIGN/METHODS

Primary cultures of basal epithelial cells were infected by coculture with mitomycin-C-treated HTLV-producer T-cell lines and HTLV-infected milk epithelial cells, and the transfer of infection was monitored by polymerase chain reaction (PCR) amplification and immunocytochemical staining.

RESULTS

Basal mammary epithelial cells were found to be susceptible to HTLV infection and capable of transferring HTLV infection to normal peripheral blood lymphocytes (PBL).

CONCLUSIONS

A reservoir for HTLV infectivity could exist in mammary epithelial cells and contribute to the introduction of HTLV infectivity into milk by infecting lymphocytes that traverse the epithelium and by the release of infected epithelial cells, infectious cell fragments, and free virions directly into the milk.

Persistent HTLV-I infection of breast luminal epithelial cells: a role in HTLV transmission?

Human T cell leukemia viruses are predominantly transmitted from mother to child by breastfeeding. Endemic levels of HTLV infection are associated with ethnic groups that have traditionally practised long-term breastfeeding. In the course of long-term lactation, we have found that human milk contains leukocytes and epithelial cells and that mixed primary cultures of these milk cells are susceptible to HTLV-I infection in vitro. We have established and characterized an immortalized line of milk epithelial cells, HTLV-LEC, that are productively infected and transformed with HTLV-I. This is the first reported case of human cells, other than T cells, that are transformed with HTLV-I. Cultures of HTLV-LEC are distinctive because of the synthesis of an extensive extracellular matrix that appears to support in vitro morphogenesis. HTLV-I infection can be transmitted from HTLV-LEC into normal epithelial cells and leukocytes. Our results suggest that infected epithelial cells could be involved in the persistence and transmission of virus infection in HTLV-I carriers.

A novel type of defective viral genome suggests a unique strategy to establish and maintain persistent lymphocytic choriomeningitis virus infections

Defective interfering RNAs have long been thought to be a causal factor of persistent RNA virus infections. Here we describe a novel type of defective genome of lymphocytic choriomeningitis virus and the unique mechanism by which these RNAs appear to contribute to the establishment and maintenance of persistent infection. The defective genomes have short deletions in the untranslated regions at their termini and additional nontemplated terminal nucleotides. This and previous work from our laboratory suggested that the RNAs were competent for replication but not for transcription. From experiments using a technique to unambiguously determine the sequences of individual RNA termini, it appears that some truncated RNAs can be repaired. The data suggest that the loss or gain of nucleotides from the RNA termini during the course of infection is the mechanism for establishing and maintaining persistence.

Differential immune recognition of LCMV nucleoprotein and glycoprotein in transgenic mice expressing LCMV cDNA genes

We have generated doubly transgenic (DT) mice that independently express cDNA genes for the nucleocapsid protein (NP) and the surface glycoproteins (GP) of lymphocytic choriomeningitis virus (LCMV). By RT-PCR, transcription of both transgenes was detected at low levels in brain and kidney but was not observed in the thymus. Additionally, transcription of the GP transgene was observed in the spleen. Following challenge with exogenous LCMV, an anti-NP CTL response was induced in LCMV-infected DT mice, suggesting that nonresponsiveness to NP had not been established. In contrast, LCMV- infected DT mice were nonresponsive to GP and failed to mount any CTL response against GP, either at Day 7 or Day 30 postinfection or following expansion of splenocyte populations in vitro. A significant number (33%) of adult DT mice survived intracerebral infection with LCMV, suggesting that virus-induced immunopathology in the central nervous system can be diminished by combined expression of the transgenes whereas no protective effect was conferred on singly transgenic mice, expressing NP or GP alone. The DT mice therefore create a novel host genetic background for comparative studies of the anti-LCMV immune responses relative to parental C57Bl/6 mice.

Infection and cellular activation by human T-cell leukemia viruses, types I and II

Resting peripheral blood mononuclear cells (PBMC) or purified T-cells can be induced to proliferate when cocultured in vitro with fixed HTLV-infected T-cells. This process of HTLV-dependent cellular activation and induction of proliferation has been considered distinctive because of an apparent independence from conventional T-cell costimulatory signals. We have examined several HTLV-infected cell lines and found that proliferation was readily induced in resting PBMC by T-cells that were productively-infected with HTLV. However, equivalent HTLV-productive infection in a B-cell line failed to induce proliferation in PBMC, suggesting that HTLV-dependent induction of proliferation in PBMC was, at least in part, dependent upon a T-cell-specific signal. Furthermore, the induction of proliferation in PBMC populations was found to overlap with, and actually require, transfer and establishment of HTLV infection within the T-cell compartment of the PBMC population. These findings suggest that virus-induced activation of target cells may be directly associated with transfer and spread of HTLV infection.

Human PKR transfected into murine cells stimulates expression of genes under control of the HIV1 or HTLV-I LTR

We have analyzed the effect of transfection into murine NIH/3T3 cells of the human dsRNA-activated kinase PKR on the expression of the beta-galactosidase reporter gene, placed under control of the HIV1 or the HTLV-I LTR. beta-Galactosidase expression is stimulated when the reporter plasmids are cotransfected with wild-type PKR but inhibited when cotransfected with a catalytically inactive mutant PKR. In the case of HIV1, beta-galactosidase expression was not stimulated when cotransfection was carried out with PKR harboring mutations in the dsRNA binding domains, indicating that stimulation depends on the classical mode of PKR activation through dsRNA binding. In contrast, the dsRNA binding mutants of PKR could still partially stimulate beta-galactosidase expression from the HTLV-I LTR, suggesting that PKR activation in this case may involve different/additional mechanisms. These results show that, in addition to the known down-regulation of protein synthesis through elF2 phosphorylation, PKR can also positively stimulate gene expression in vivo, most probably through phosphorylation of a substrate distinct from elF2.

Lymphocytic choriomeningitis virus-induced immune dysfunction: induction of and recovery from T-cell anergy in acutely infected mice

Acute infection of immunocompetent mice by lymphocytic choriomeningitis virus induces a potent cytotoxic T-lymphocyte response that eliminates infectious virus. Concurrently and paradoxically, there is a general suppression of lymphocyte responses to mitogens and to other infectious agents. Splenocytes from infected mice released significant amounts of gamma interferon in response to mitogenic stimulation in vitro, but neither interleukin 2 nor interleukin 4 was similarly elevated relative to the amounts released by control cells. Early T-cell receptor-proximal signaling events were found to be intact, confirming that the cells were viable and had received the mitogenic stimuli in an appropriate manner. Acutely infected adult thymectomized mice regained concanavalin A responsiveness in parallel with euthymic mice, if T cells were left unmanipulated for several weeks after clearance of virus from the mice. Therefore, although acute lymphocytic choriomeningitis virus infection has the effect of disrupting proliferation when the T-cell receptor is ligated, this state is only temporary. In contrast, T cells from persistently infected adult mice reveal long-lasting alterations in concanavalin A responsiveness.

Sequence heterogeneity in the termini of lymphocytic choriomeningitis virus genomic and antigenomic RNAs

Sequence analysis of lymphocytic choriomeningitis virus L and S RNAs has revealed evidence of heterogeneity within the termini of the genomic and antigenomic RNAs. The RNAs are missing from 0 to 38 bases, show characteristic patterns of deleted nucleotides at both 5' and 3' termini, and often have a nontemplated base at the terminus. The same deletions, at either the 5' or the 3' terminus of the genomic L and S RNAs, are frequently found in the complementary strand of antigenomic RNA, suggesting that RNAs with deleted termini may be recognized as functional templates for replication. RNAs extracted from virions, or viral nucleocapsids isolated from acutely infected cells, are similar in the nature and extent of terminal heterogeneity that have been observed. This finding brings into question the function of the conserved sequences located at the termini of arenavirus genomic RNAs. Our data suggest that, while replication and packaging of the genomic and antigenomic RNA molecules can occur with terminally deleted molecules, mature transcripts may be derived only from full-length templates containing the conserved terminal sequence.

Macrophages in mice acutely infected with lymphocytic choriomeningitis virus are primed for nitric oxide synthesis

Following infection of adult mice with lymphocytic choriomeningitis virus (LCMV) there is a well documented suppression of T-cell and B-cell functions concurrent with the strong anti-LCMV immune response. Macrophages have been shown to be infected and activated during acute LCMV infection and there is some evidence to indicate that there is altered antigen presentation in acutely infected mice. We have examined nitric oxide (NO) production by splenic macrophages during acute infection of adult mice. Our results show that these macrophages are primed for production of NO, that the inducible production of NO parallels the immune suppression, and that NO production is dependent on the presence of IFN gamma. However, neither in vivo nor in vitro treatment with N-monomethyl-L-arginine (NMA), a specific inhibitor of nitric oxide synthase, altered the induction or maintenance of virus-induced immune suppression in mice acutely infected with LCMV.

Trafficking of activated cytotoxic T lymphocytes into the central nervous system: use of a transgenic model

We have used cell or tissue-specific promoters to express lymphocytic choriomeningitis virus (LCMV) proteins in selected cells in independent lines of transgenic mice. Upon adoptive transfers into these mice, MHC-restricted LCMV-specific cytotoxic T lymphocytes homed specifically to either the choroid plexus (SV40 promoter) or beta cells of the islets of Langerhans (rat insulin promoter). The availability of promoters specific for neurons, oligodendrocytes and astrocytes makes this approach compelling for evaluating T cell trafficking into the CNS and for analyzing antigen presentation in vivo in the CNS.

Lymphocytic choriomeningitis virus induces a chronic wasting disease in mice lacking class I major histocompatibility complex glycoproteins

Lymphocytic choriomeningitis virus (LCMV) induces a chronic, wasting syndrome when injected intracerebrally into H-2b mice homozygous for a beta 2-microglobulin (beta 2-m (-/-)) gene disruption. These mice have very few CD8+ T cells and express little class I MHC glycoprotein, though minimal levels of the H-2Db molecule have been detected on in vitro cultured beta 2-m (-/-) cells. The underlying immunopathological process in these beta 2-m (-/-) mice is mediated by virus immune CD4+ effectors. However, adoptively transferred CD8+ T cells from normal, LCMV-infected H-2Db compatible donors induce significant (but low level) meningitis in beta 2-m (-/-) recipients. Such mice develop neither the neurological disease characteristic of LCM nor the persistent, though generally non-fatal, debility that occurs when only the CD4+ T cell subset is involved.

Concurrent sequence analysis of 5' and 3' RNA termini by intramolecular circularization reveals 5' nontemplated bases and 3' terminal heterogeneity for lymphocytic choriomeningitis virus mRNAs

We have used a technique of RNA circularization coupled with polymerase chain reaction amplification for simultaneous analysis of the 5' and 3' termini of subgenomic mRNAs derived from the S RNA of lymphocytic choriomeningitis virus during an acute infection of BHK cells. These mRNAs possess 1 to 7 nontemplated nucleotides of apparently random sequence at their 5' ends. The predominant mRNA species have 4 or 5 nontemplated nucleotides. The 5' termini of the mRNAs also have properties consistent with the presence of a 5' cap structure. The 3' termini of the mRNAs lack poly(A) tails, and we have shown that transcription termination occurs at heterogeneous positions within the intergenic region of the S RNA. The identification of several distinct termini in the vicinity of a putative stem-loop structure in the RNA templates suggests that transcription termination may be mediated by a structural signal rather than a precise sequence signal.

Detection of virus-specific RNA-dependent RNA polymerase activity in extracts from cells infected with lymphocytic choriomeningitis virus: in vitro synthesis of full-length viral RNA species

We have developed an in vitro assay for the lymphocytic choriomeningitis virus (LCMV) RNA-dependent RNA polymerase with ribonucleoprotein complexes extracted from acutely infected tissue culture cells. The RNA products synthesized in vitro corresponded in size to the full-length genomic L and S RNAs and subgenomic NP and GP mRNAs normally produced in vivo during acute LCMV infection. In a temporal analysis spanning the first 72 h of acute infection, the in vitro polymerase activity of ribonucleoprotein complexes was maximal at 16 h and declined significantly at later times. In contrast, the intracellular levels of the viral L protein (the putative polymerase protein) appeared to be maximal at 48 to 72 h postinfection. Our results suggest that the accumulation of L protein correlates with reduced viral replication and transcription at later times in acute infection and may be involved in the transition from acute to persistent LCMV infection.

Molecular characterization of a cloned dolphin mitochondrial genome

DNA clones have been isolated that span the complete mitochondrial (mt) genome of the dolphin, Cephalorhynchus commersonii. Hybridization experiments with purified primate mtDNA probes have established that there is close resemblance in the general organization of the dolphin mt genome and the terrestrial mammalian mt genomes. Sequences covering 2381 bp of the dolphin mt genome from the major noncoding region, three tRNA genes, and parts of the genes encoding cytochrome b, NADH dehydrogenase subunit 3 (ND3), and 16S rRNA have been compared with corresponding regions from other mammalian genomes. There is a general tendency throughout the sequenced regions for greater similarity between dolphin and bovine mt genomes than between dolphin and rodent or human mt genomes.

Genetic analysis of in vivo-selected viral variants causing chronic infection: importance of mutation in the L RNA segment of lymphocytic choriomeningitis virus

Viral variants with different biological properties are present in the central nervous systems (CNS) and lymphoid tissues of mice persistently infected with lymphocytic choriomeningitis virus (LCMV). Viral isolates from the CNS are similar to the original Armstrong LCMV strain and induce potent virus-specific T-cell responses in adult mice, and the infection is rapidly cleared. In contrast, LCMV isolates derived from spleens of carrier mice cause persistent infections in adult mice. This chronic infection is associated with low levels of antiviral T-cell responses. In this study, we genetically characterized two independently derived spleen variants by making recombinants (reassortants) between the spleen isolates and wild-type (wt) LCMV and showed that the ability to persist in adult mice and the associated suppression of T-cell responses segregates with the large (L) RNA segment. In addition, we analyzed a revertant (isolated from the CNS) derived from one of the spleen variants. By comparing the biological properties of three reassortants that contained the same S segment but had the L segment of either the original wt Armstrong LCMV, the spleen variant derived from it, or the CNS revertant derived from the spleen variant, we were able to show unequivocally that biologically relevant mutations occurred in the L segment not only during generation of the spleen variant from wt LCMV but also in reversion of the spleen variant to the wt phenotype. Thus, our results showed that (i) genetic alterations in the L genomic segment were involved in organ-specific selection of viral variants, and (ii) these mutations profoundly affected the ability of LCMV to cause chronic infections in adult mice.

Deleted viral RNAs and lymphocytic choriomeningitis virus persistence in vitro

Lymphocytic choriomeningitis virus (LCMV) infection of most tissue culture cell lines results in a non-cytopathic persistent infection. Persistent infections in vitro share many characteristics with persistent LCMV infection of mice; both are associated with decreased titres of infectious virus, restricted accumulation of viral glycoproteins at the surface of infected cells and the generation of interfering particles. We have used gel electrophoresis and hybridization techniques to analyse LCMV gene expression during persistent infection of a number of tissue culture cell lines. Our study has demonstrated that, although deleted viral RNAs can be detected during persistent LCMV infection in vitro, there may not be an obligatory association between deleted RNAs and persistence. In addition, we have found that LCMV interfering activity can be produced in the apparent absence of deleted intracellular viral RNAs.

Molecular analysis of viral RNAs in mice persistently infected with lymphocytic choriomeningitis virus

Infection of newborn mice with lymphocytic choriomeningitis virus (LCMV) results in a lifelong persistent infection. Persistently infected animals continuously produce low levels of infectious virus and accumulate large amounts of intracellular viral nucleic acid (P. J. Southern, P. Blount, and M. B. A. Oldstone, Nature [London] 312:555-558, 1984). We have used gel electrophoresis and hybridization techniques to analyze viral RNAs that appear during the establishment and maintenance of a persistent LCMV infection in vivo to identify any role for defective and/or defective interfering RNAs. We have found a complex, heterogeneously sized population of viral RNAs in multiple independent tissues that is uniquely associated with persistent infections in vivo, but we have not yet established whether these RNAs have a causal or a consequential association with persistent infection by LCMV. Within the complex virus RNA population, full-length genomic L and S RNAs were readily detectable and represented the most abundant individual viral RNA species. RNAs apparently corresponding in size to the viral nucleoprotein and glycoprotein mRNAs could also be detected in these tissue RNA samples. The presence of glycoprotein mRNA indicates a potential mechanism of posttranscriptional regulation to account for the previously documented restriction in viral glycoprotein expression in persistently infected mice (M. B. A. Oldstone and M. J. Buchmeier, Nature (London) 300:360-362, 1982).

Virus-lymphocyte interactions. II. Expression of viral sequences during the course of persistent lymphocytic choriomeningitis virus infection and their localization to the L3T4 lymphocyte subset

Viruses that cause in vivo persistent infections need to selectively compromise the host's immunologic surveillance machinery in order to survive. To understand the molecular basis of how this is accomplished we have analyzed persistent virus infection by lymphocytic choriomeningitis in its normal host, the mouse. Earlier we noted by infectious center analysis that five in 10(4) lymphocytes carried by persistently infected mice contained infectious materials throughout the course of infection. A previous publication extended these results, in BALB mice by showing that the L3T4+ lymphocyte subset in lymph nodes and spleens was predominantly involved. Using cDNA labeled probes to the viral genome and in situ hybridization we report that 1 to 2% of circulating lymphocytes from several mouse strains contain viral RNA sequences for the three viral structural genes. By FACS analysis, the Thy-1.2+, L3T4+ subset primarily harbors virus while viral sequences are usually not detected in the Lyt-2+ subset as early as 6 days after initiating infection in newborns and throughout the course of the persistence. These findings suggest that incomplete, presumably defective, virus is generated in a subset of Th lymphocytes during persistent infection and that during this time infection of cytotoxic T cell subsets is minimal.

Virus-lymphocyte interactions. II. Expression of viral sequences during the course of persistent lymphocytic choriomeningitis virus infection and their localization to the L3T4 lymphocyte subset

Viruses that cause in vivo persistent infections need to selectively compromise the host's immunologic surveillance machinery in order to survive. To understand the molecular basis of how this is accomplished we have analyzed persistent virus infection by lymphocytic choriomeningitis in its normal host, the mouse. Earlier we noted by infectious center analysis that five in 10(4) lymphocytes carried by persistently infected mice contained infectious materials throughout the course of infection. A previous publication extended these results, in BALB mice by showing that the L3T4+ lymphocyte subset in lymph nodes and spleens was predominantly involved. Using cDNA labeled probes to the viral genome and in situ hybridization we report that 1 to 2% of circulating lymphocytes from several mouse strains contain viral RNA sequences for the three viral structural genes. By FACS analysis, the Thy-1.2+, L3T4+ subset primarily harbors virus while viral sequences are usually not detected in the Lyt-2+ subset as early as 6 days after initiating infection in newborns and throughout the course of the persistence. These findings suggest that incomplete, presumably defective, virus is generated in a subset of Th lymphocytes during persistent infection and that during this time infection of cytotoxic T cell subsets is minimal.

Analyses of the cytotoxic T lymphocyte responses to glycoprotein and nucleoprotein components of lymphocytic choriomeningitis virus

The outcome of infection by lymphocytic choriomeningitis virus (LCMV) in the natural murine host is determined in large part by the cytotoxic T lymphocyte response (CTL) mounted by the host. In order to define the specificities of CTL induced by LCMV infection, we have cloned and expressed the full-length nucleoprotein (NP) gene and 75% of the glycoprotein (GP) gene of LCMV in vaccinia virus vectors and have used these recombinant viruses to sensitize syngeneic target cells to lysis by anti-LCMV CTL. We have studied the anti-LCMV CTL responses induced on three different mouse H2 (major histocompatibility complex) backgrounds. First, we find that the relative recognition of the two LCMV proteins differs markedly on different H2 haplotypes; both proteins are seen on the H2bb background, while only NP is recognized on two other haplotypes (H2dd and H2qq). Second, we show that on the H2bb background the anti-GP CTL response comprises a major component of the overall CTL response, in marked contrast to several other viruses, e.g., influenza virus, vesicular stomatitis virus, and respiratory syncytial virus where anti-GP responses, if present, comprise only a minor portion of the whole. Third, LCMV GP can be a major target antigen for CTL induced by a serotypically distinct strain of LCMV, again in contrast to the above virus systems in which CTL cross-reactivity among different serotypes is dependent largely on the recognition of "internal" proteins.

Temporal analysis of transcription and replication during acute infection with lymphocytic choriomeningitis virus

We have analyzed the accumulation of viral genomic and messenger RNAs in tissue culture cells during the first 24 hr of acute infection with lymphocytic choriomeningitis virus (LCMV). This has allowed comparison of the relative amounts of the genomic L and S RNAs (both genomic sense and genomic complementary sense) and of nucleoprotein (NP) and glycoprotein precursor (GP-C) mRNAs. Using these techniques NP mRNA was detected simultaneously with genomic S RNA, but the amount of NP mRNA accumulating during this period of infection was higher than that of GP-C mRNA. This is consistent with a model for ambisense RNA transcription and replication proposed by D.D. Auperin, V. Romanowski, M. Galinski and D. H. L. Bishop (J. Virol. 52: 897-904, 1984). The accumulation of S RNA exceeded that of L RNA and, for both L and S RNAs, the amount of genomic sense RNA was higher than that of genomic complementary RNA.

Analysis of the genomic L RNA segment from lymphocytic choriomeningitis virus

The arenavirus genomic L RNA segment represents approximately 70% of the viral genetic material but current understanding of the organization, regulation, and functioning of the viral L products remains limited. Biological studies with reassortant viruses have implicated the L RNA segment in the lethal infection of adult guinea pigs produced by LCMV-WE but no further explanation of the pathogenic process is presently available. We have initiated a detailed molecular analysis of LCMV L products based on construction and characterization of L-specific cDNA clones and synthesis of L-specific hybridization probes. Nucleotide sequencing studies have allowed the derivation of a partial amino acid sequence for a predicted L protein and antisera raised against synthetic peptides have demonstrated an L protein in Western blotting experiments. Using this approach we have identified a single high molecular weight protein (approximately 200,000 Da) in purified virions and in viral ribonucleoprotein complexes extracted from acutely infected tissue culture cells. This L protein is translated from a nonpolyadenylated, genomic complementary L mRNA and potentially represents part or all of the viral RNA-dependent RNA polymerase.

Site-specific antibodies define a cleavage site conserved among arenavirus GP-C glycoproteins

Arenaviruses share a common strategy for glycoprotein synthesis and processing in which a mannose-rich precursor glycoprotein, termed GP-C in lymphocytic choriomeningitis virus (LCMV), is posttranslationally processed by oligosaccharide trimming and proteolytic cleavage to yield two structural glycoproteins, GP-1 and GP-2. Mapping the orientation and proteolytic cleavage site(s) in such polyproteins has traditionally required direct protein sequencing of one or more of the cleaved products. This technique requires rigorous purification of the products for sequencing and may be complicated by amino-terminal modifications which interfere with sequence analysis. We used an alternative approach in which synthetic peptides corresponding to sequences bracketing a potential protease cleavage site were used to raise antisera which define the boundaries of the cleaved products. We found that cleavage of LCMV GP-C to yield GP-1 and GP-2 occurs within a 9-amino-acid stretch of GP-C which contains a paired basic amino acid group -Arg-Arg-, corresponding to amino acids 262 to 263 in the LCMV GP-C sequence. By comparison with the predicted amino acid sequences of a second LCMV strain, LCMV-WE, as well as with the deduced amino acid sequences of the New World arenavirus Pichinde and the Old World virus Lassa, we observed similar conservation of paired basic and flanking amino acid sequences among these viruses.

Molecular characterization of the genomic S RNA segment from lymphocytic choriomeningitis virus

We have used cDNA clones derived from the genomic S RNA segment of lymphocytic choriomeningitis virus (LCMV), Armstrong strain, as hybridization probes to monitor virus gene expression during acute infections. Our results with strand-specific probes confirm the ambisense character of the LCMV S RNA segment and document the presence of both genomic sense and genomic complementary sense RNA species over the time course of infection. We have used nucleotide sequence information to predict primary amino acid sequences for the major viral structural proteins, nucleoprotein (NP) and glycoprotein (GP-C). Antibodies raised against synthetic peptides derived from these predicted protein sequences have indicated that the gene order for the S segment is 3' NP----5' GP-C and provided direct demonstration that the GP-1 portion of the GP-C precursor is encoded nearest the 5' end of the S segment. Comparison of the predicted amino acid sequences for NP and GP-C between the Armstrong CA-1371 strain and the WE strain shows over 90% amino acid identity. This suggests that significant differences described for the pathogenic potential of the Arm and WE strains in C3H mice reside in one or a very few critical amino acid changes.

Dissecting the molecular anatomy of the nervous system: analysis of RNA and protein expression in whole body sections of laboratory animals

Nucleic acid hybridization and protein blotting procedures have allowed the specific detection of both RNA and protein gene products in whole body sections of a selected host. These procedures permit efficient and reproducible screening of both endogenous and exogenous (viral) gene products, thus facilitating the study of normal differentiation, the localization of virus and the monitoring of viral diseases. Although success with RNA hybridization has thus far been limited to exogenous viral gene expression, the protein immunoblotting procedures have the sensitivity to detect endogenous protein products with high resolution. These combined procedures should prove useful for the study of protein expression in numerous developmental systems.

Cytoimmunotherapy for persistent virus infection reveals a unique clearance pattern from the central nervous system

The mechanism(s) by which infectious or malignant material is cleared by the host has long been an area of intensive study. We have used the murine model of infection with lymphocytic choriomeningitis virus (LCMV) to look at immune clearance during persistent infection. LCMV was selected because the mouse is its natural host, it easily induces acute or persistent infection in vivo, and the mechanism by which it is cleared in vivo during acute infection is now well understood. Clearance, although associated with several antiviral immune effector mechanisms, is primarily dependent on the activity of virus-specific cytotoxic T lymphocytes (CTL) restricted by H-2 molecules of the mouse major histocompatibility complex (MHC). If these cells fail to generate or are depleted, progression from acute to persistent infection occurs. Here, using molecular probes, we show that viral nucleic acid sequences, viral proteins and infectious materials can be efficiently and effectively cleared by adoptive transfer of antiviral H-2-restricted lymphocytes bearing the Lyt 2+ phenotype. Viral materials are cleared from a wide variety of tissues and organs where they normally lodge during persistent infection. Unexpectedly, the mode by which viral materials are removed from the central nervous system (CNS) differed markedly from the mechanism of clearance occurring at other sites. These observations indicate the possible use of adoptive lymphocyte therapy for treatment of persistent infections and suggest that immune clearance of products from the CNS probably occurs by a process distinct from those in other organs.

Biology of cloned cytotoxic T lymphocytes specific for lymphocytic choriomeningitis virus. V. Recognition is restricted to gene products encoded by the viral S RNA segment

Lymphocytic choriomeningitis virus (LCMV) Armstrong (ARM) strain-specific, H-2d-restricted CTL effectively lyse syngeneic targets infected by LCMV ARM, but show reduced killing of LCMV Pasteur (PAST) strain-infected H-2d cells. We have reassorted the two RNA segments, large (L) and small (S), of LCMV ARM and PAST to generate LCMV with genotypes of L ARM/S PAST and L PAST/S ARM. By using these reassortants and both LCMV primary CTL and CTL clones, we report that the induction, recognition, and lysis of LCMV-specific CTL depend on the S RNA segment and the genes it encodes.

Biology of cloned cytotoxic T lymphocytes specific for lymphocytic choriomeningitis virus. V. Recognition is restricted to gene products encoded by the viral S RNA segment

Lymphocytic choriomeningitis virus (LCMV) Armstrong (ARM) strain-specific, H-2d-restricted CTL effectively lyse syngeneic targets infected by LCMV ARM, but show reduced killing of LCMV Pasteur (PAST) strain-infected H-2d cells. We have reassorted the two RNA segments, large (L) and small (S), of LCMV ARM and PAST to generate LCMV with genotypes of L ARM/S PAST and L PAST/S ARM. By using these reassortants and both LCMV primary CTL and CTL clones, we report that the induction, recognition, and lysis of LCMV-specific CTL depend on the S RNA segment and the genes it encodes.

Genetic mapping of lymphocytic choriomeningitis virus pathogenicity: virulence in guinea pigs is associated with the L RNA segment

The Armstrong CA 1371 (ARM) and WE strains of lymphocytic choriomeningitis virus (LCMV) differ in the ability to produce disease in adult guinea pigs. Infection with the ARM strain is not lethal, even at high virus doses (greater than 10,000 PFU), whereas the WE strain causes 100% mortality even at low doses (less than 10 PFU). To determine the genetic basis of this virulence, intertypic reassortants were made between the ARM and WE strains of LCMV. The two reassortants with the genotypes WE/ARM (L segment of WE and S segment of ARM) and ARM/WE (L segment of ARM and S segment of WE) were tested for their pathogenicity in guinea pigs. The ARM/WE reassortant was avirulent like the ARM/ARM parental strain. Minimal viral replication was observed in organs of guinea pigs inoculated with 10(2) or 10(5) PFU of ARM/ARM or ARM/WE, and all animals survived. In contrast, the WE/ARM reassortant was highly virulent like the WE/WE parental strain and killed all of the infected animals. High levels of viral replication were observed in guinea pigs infected with the latter two strains. In contrast to these in vivo observations, both the parental strains and the ARM/WE or WE/ARM reassortants had similar growth potential in cultured guinea pig fibroblasts. Thus, the L RNA segment of LCMV WE is important for viral replication in vivo and is associated with fatal acute disease after infection of adult guinea pigs.

The S RNA segment of lymphocytic choriomeningitis virus codes for the nucleoprotein and glycoproteins 1 and 2

The lymphocytic choriomeningitis virus (LCMV) genome consists of a large RNA segment and a small RNA segment. The three major structural proteins of this virus are an internal nucleoprotein and two surface glycoproteins. Intertypic reassortants between the Armstrong and WE strains of LCMV were made to map proteins encoded by the LCMV genome segments. Using monoclonal antibodies specific for the nucleoprotein and the glycoproteins of WE and Armstrong, we showed that the small RNA segment of LCMV codes for the three major structural polypeptides.

Analysis of persistent virus infections by in situ hybridization to whole-mouse sections

Nucleic acid hybridization techniques have contributed significantly to the understanding of gene organization, regulation and expression. In the context of persistent or latent viral infections, hybridization with specific labelled probes represents the most sensitive assay presently available for detection of viral genomes. During the course of persistence, viral genomes may exist in multiple and yet quite segregated areas in an infected host, but examination of all tissues remains difficult and time-consuming. At present, the application of hybridization assays to in vivo infections requires either chemical extraction of nucleic acid coupled with dot-blot and gel transfer techniques or in situ hybridization to cryostat tissue sections. In both cases, selected tissues must be removed by dissection before analysis. We describe here a procedure which allows efficient and reproducible screening of all tissue in an infected host. Our technique allows detection of viral genetic material in whole-body sections of infected mice, and provides the first evidence in vivo for accumulation of viral genetic material with a parallel decrease in infectious virus during persistent virus infection. This technique should be widely applicable to studies of developmental regulation of gene expression, for monitoring locations of gene expression in transgenic mice and for analysis of molecular mechanisms in pathogenesis.

Analysis of gene expression using simian virus 40 vectors

Extensive studies on the DNA tumor virus Simian Virus 40 (SV40) have provided a wealth of information regarding the genome organization, regulation of viral gene expression, and the mechanism of DNA replication. SV40 can grow lytically in permissive monkey cells or the viral DNA can integrate into the host genome of nonpermissive rodent cells causing morphological transformation. The viral DNA exists as a minichromosome within the nuclei of lytically infected cells and, as a consequence of DNA replication, there is a significant amplification of the viral genome during infection. These properties suggested that SV40 could be developed as a transducing vector to introduce exogenous DNA into mammalian cells and to express this foreign DNA during the SV40 infectious cycle. In this article the properties of SV40 virus vectors and SV40 hybrid plasmid vectors are described and contrasted.