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

Virus infection triggers insulin-dependent diabetes mellitus in a transgenic model: role of anti-self (virus) immune response

We investigated the potential association between viruses and insulin-dependent (type 1) diabetes (IDDM) by developing a transgenic mouse model. By inserting into these mice a unique viral protein that was then expressed as a self-antigen in the pancreatic islets of Langerhans, we could study the effect on that expressed antigen alone, or in concert with an induced antiviral (i.e., autoimmune) response manifested later in life in causing IDDM. Our results indicate that a viral gene introduced as early as an animal's egg stage, incorporated into the germline, and expressed in islet cells does not produce tolerance when the host is exposed to the same virus later in life. We observed that the induced anti-self (viral) CTL response leads to selective and progressive damage of beta cells, resulting in IDDM.

Molecular basis of viral persistence: a single amino acid change in the glycoprotein of lymphocytic choriomeningitis virus is associated with suppression of the antiviral cytotoxic T-lymphocyte response and establishment of persistence

Isolates of lymphocytic choriomeningitis virus (LCMV) that elicit a cytotoxic T-lymphocyte response (CTL+) have been compared with isolates that suppress the CTL response (CTL-) in an effort to map this phenotype. A single amino acid change in the glycoprotein of the LCMV Armstrong (ARM) strain is consistently associated with the CTL- trait and the ability of the virus to persist (P+). The CTL+ P- parental strain spontaneously gives rise to CTL- P+ variants within lymphoid tissues of mice persistently infected from birth. To map the structural basis of the phenotype, the complete RNA sequence of LCMV ARM 53b (CTL+) was compared with that of its variant ARM clone 13 (CTL-). Differences in 5 of 10,600 nucleotides were found. Three changes are noted in the large L RNA segment, and two are noted in the small S RNA segment. Only two of the changes distinguishing CTL+ from CTL- isolates affect amino acid coding: lysine to glutamine at amino acid 1079 of the polymerase protein, and phenylalanine to leucine at amino acid 260 of the envelope glycoprotein (GP). We also analyzed two additional CTL- variants and four spontaneous CTL+ revertants. All three CTL- variants differ from the original CTL+ parental strain at GP amino acid 260, indicating that this amino acid change is consistently associated with the CTL- phenotype. By contrast the other four mutations in LCMV are not associated with the CTL- phenotype. Sequence analysis of the coding regions of four CTL+ revertants of ARM clone 13 did not reveal back mutations at the GP 260 locus. This finding indicates that the GP 260 mutation is necessary but not sufficient for a CTL- P+ phenotype and that the reversion to CTL+ P- is likely either due to secondary mutations in other regions of the viral genome or to quasispecies within the revertant population that make significant contributions to the phenotype.

Protection of mice from a lethal coronavirus infection in the central nervous system by adoptive transfer of virus-specific T cell clones

The protective effect of a mouse hepatitis virus type-4 (MHV-4)-specific CD8+ cytotoxic T cell clone and a CD4+ helper T cell clone was examined by the adoptive transfer into brains of mice lethally infected with MHV-4. Mice survived acute encephalitis if more than 5 x 10(5) cells of either type of the virus-specific T cell clones had been transferred into H-2-matched recipients by 1 day post-infection. Although the adoptive transfer of both types of the T cell clones suppressed viral growth and viral antigen-positive cells in the brains, a significant inhibition of virus replication by the cytotoxic T cell clone was detected prior to that induced by the helper T cell clone. Histologically, cell destruction was prominent in the brains of mice which received the cytotoxic T cell clone. These results demonstrate that both the CD8+ cytotoxic T cell and the CD4+ helper T cell can protect mice from a lethal MHV-4 infection in the central nervous system.

Paramyxovirus infections alter certain functional properties in cultured sensory neurons

Functional properties of cultured mouse dorsal root ganglion cells infected with paramyxoviruses have been studied using intracellular recording techniques. Mumps virus, which causes a persistent non-lytic infection, and Sendai virus, which causes an infection that leads to cell lysis after about a week were used. In the early phase of the infection (24-48 h) both viruses caused a reduction in the influx of calcium ions during the action potential, but did not alter resting membrane potential, action potential amplitude or input resistance. At later times functional properties became normal in mumps infected neurons. In contrast, Sendai virus infected neurons showed a reduction of action potential amplitude and input resistance at 48-72 h after infection, and finally there was also a reduction of membrane potential before the cells disintegrated. These results show that different paramyxovirus infections may cause different types of alterations in the functional properties of neurons. The reduced calcium influx resulting from mumps infection suggests that a non-lytic viral infection may have selective effects on important regulators of neuronal functions. Moreover, a lethal viral infection (Sendai) may influence specific membrane properties, such as calcium channel activation, several days prior to general structural and functional degeneration.

Viral expression in experimental canine distemper demyelinating encephalitis

We have characterized the relationship between the expression of canine distemper virus (CDV) and demyelinating lesions in the white matter of the cerebellum of experimentally infected dogs. In animals which had demyelinating lesions, CDV proteins (N, P, F and H) were expressed and infectious virus could be recovered from brain tissue. Viral proteins (N, P, F and H) were detected by monoclonal antibodies and immunocytochemistry within demyelinating lesions as well as in scattered glial cells in areas of the white matter which lacked detectable lesions. Many cell types, including astrocytes, neurons, ependymal cells, choroid plexus cells, meningeal cells and perivascular inflammatory cells were labelled for viral antigen. We conclude from our results that the mechanism of demyelination in canine distemper virus-induced encephalitis involves expression of viral gene products at the lesion site.

Genetic basis of viral persistence: single amino acid change in the viral glycoprotein affects ability of lymphocytic choriomeningitis virus to persist in adult mice

This study has identified a single amino acid change in the viral glycoprotein that profoundly affects the ability of lymphocytic choriomeningitis virus (LCMV) to persist in its natural host. Adult immunocompetent mice infected with a variant of the Armstrong strain, spleen isolate clone 13 (svA/svA), harbor virus for several months and exhibit suppressed T cell responses. In contrast, adult mice infected with a reassortant virus (svA/wtA) that contains the L segment of the spleen variant and the S segment of the parental wt Armstrong, make potent LCMV-specific CTL responses and clear the infection within 2-4 wk. These two viruses, spleen variant clone 13 and the reassortant svA/wtA, are identical in their noncoding regions and show no amino acid changes in any of their viral genes except for one substitution in the glycoprotein. The reassortant virus svA/wtA has a phenylalanine at amino acid residue 260 of the glycoprotein, whereas the spleen variant clone 13 has a leucine at this position. This study constitutes one of the first reports defining the genetic basis of viral persistence at the whole animal level, and identifying a single mutation that markedly increases the ability of a virus to persist in its natural host.

Viral persistence and immune dysfunction

Viruses can persist for years without provoking an effective host immune response or otherwise causing the cell destruction characteristic of an acute viral infection. Clinically relevant principles, generalizable to many persistent viruses, are exemplified by measles and lymphocyte choriomeningitis viruses. The LCMV model indicates that viral persistence and the anergic state are reversible.

The influence of cold or isolation stress on resistance of mice to West Nile virus encephalitis

The effect of cold or isolation stress on mortality rate and brain virus level were investigated in mice infected with West Nile virus (WNV). Exposure of mice for 5 min/day to cold water (1 +/- 0.5 degrees C) for 8-10 days resulted in 92% mortality as compared to 47% in control mice (p less than 0.001). Mice housed in individual cages (isolation stress) were also more susceptible to WN viral infection, as shown by increased mortality rate reaching 85% as compared to 50% in mice housed 6 per cage (p less than 0.01). Cold or isolation stress increased blood brain and spleen virus levels as early as 2 days after inoculation. After 8 days of isolation or cold stress, mice inoculated with WNV had 8.9 and 9.0 log10 plaque forming units in the brain, respectively, as compared to 6.9 in the control (p less than 0.01-0.001). Furthermore, lymphoid organs such as spleen and thymus showed severe mass loss. These data suggest that physical or non-physical stress situations enhance WNV encephalitis by accelerating virus proliferation and increase mortality in mice.

Adult human glial cells can present target antigens to HLA-restricted cytotoxic T-cells

T-lymphocyte recognition of antigen either on antigen-presenting cells (APC) necessary for the generation of an immune response or on target cells during the effector phase of a cellular immune response requires expression of HLA molecules. Although immune mechanisms operate in many disease processes of the central nervous system (CNS), cells of the CNS generally express low levels of HLA molecules. In this study, the potential for upregulation of HLA molecules on adult human glial cells was examined. Moreover, the functional implication of this upregulation was assessed by the capacity of glial cells to process and present target antigens to HLA class I-restricted influenza-specific and class II-restricted myelin basic protein (MBP)-specific CTL lines. Glial cells cultured from adult human surgical brain specimens or cells from established glioblastoma multiforme cell lines were studied. Lysis by antigen-specific CTLs was dependent on treatment of the target cell with interferon-gamma. The lysis was HLA restricted and antigen specific. The results indicate that adult human glial cells can process and present antigen to HLA-restricted CTLs but require the upregulation of HLA molecules. These findings have implications for infectious and autoimmune diseases of the CNS.

Astrocytic reaction predominance in chronic encephalitis of Junin virus-infected rats

Junin virus antigen distribution and astrocytic reaction to prolonged infection were characterized in rat brain by the PAP technique. During the acute stage of neurologic disease following intracerebral inoculation, Junin antigen was detected in 100% of animals, strongly in most neurons but also to a much lesser degree in scattered astrocytes, dropping to 20% of rats at 540 days postinfection. Initially labeled in all brain areas, viral antigen gradually disappeared from hippocampus but persisted irregularly in cerebral cortex, basal ganglia, Purkinje cells, pons, and medulla oblongata. Such a pattern suggests that specific neuronal subpopulations, in spite of apparently unaltered cell morphology, may persistently harbor the virus, leading on occasion to a delayed neurologic syndrome. During both the acute and chronic stages of disease, a mild inflammatory exudate was observed, characterized by the presence of T and B lymphocytes, as well as macrophages and unidentified round cells. GFAP immunostaining showed increased astrocytic reaction as infection lapsed into chronicity. Corpus callosum, hippocampus, and cerebellum exhibited the sharpest reactive astrocytosis, followed by basal ganglia, pons, and medulla oblongata, whereas in cerebral cortex it was considerably less. Astrocyte activation, which failed to correlate with viral antigen presence in neurons, seems to result from a generalized condition, possibly including diffusible brain factors triggered by viral infection. Such widespread astroglial reaction may thus contribute to the outcome of the late neurologic syndrome.

Nucleosomal fragments in serum may directly reflect cell-mediated cytotoxic activity in vivo

In in vitro experiments the activity of cytotoxic T-cells and natural killer cells has been shown to cause nuclear DNA fragmentation leading to the release of nucleosomal multimers from the target cells. These multimers form a ladder-like pattern with a periodicity of approximately 200 bp during gel electrophoresis. The objective of the present study was to show the relevance of the presence of these nucleosomal multimers in vivo during diseases that show cell-mediated cytotoxicity. Nucleosomal multimers (n greater than 5) could be detected using nick translation followed by electrophoresis in a series of sera of a chimpanzee infected with hepatitis A virus and in sera drawn from several hepatitis B patients. The multimers were present during periods expected to show an increased activity of cell-mediated cytotoxicity in the liver. During these periods the injury of the liver cells was also mirrored by the classical parameter, the release of a specific liver enzyme into the serum. The liver enzyme activity in the serum and the detection of the nucleosomal multimers did not completely overlap, however. It is postulated that the proposed nick translation assay is useful as a simple diagnostic test for cell-mediated cytotoxicity since it reflects this activity under different in vivo situations.

Trojan horse lymphocytes: a vesicular stomatitis virus-specific T-cell clone lyses target cells by carrying virus

We have isolated a vesicular stomatitis virus (VSV)-specific CD4+ CD8- murine T-cell clone. This clone proliferates only in response to VSV and lyses infected tumor cells bearing class II major histocompatibility antigens in short-term chromium release assays. In addition, the cell has VSV antigens on its surface and is capable of killing uninfected tumor cells without major histocompatibility antigen restriction in a 2-day assay. This latter cytolytic activity is eliminated by anti-VSV antibody, indicating that its lytic activity is provided by the virus. [35S]methionine labeling and immunoprecipitation experiments demonstrated that viral protein translation is initiated after incubation of the clone with a tumor target cell, defining this as the mechanism of its cytolytic activity.

Class I MHC can present an endogenous peptide to cytotoxic T lymphocytes

Since class I MHC glycoproteins may function by "screening and selecting" degraded proteins, we wished to determine whether very short peptides made within a cell were detected and bound by MHC, and presented for T cell perusal. We show that a 22 amino acid viral sequence containing a Db-restricted nonameric CTL epitope is sufficient to direct CTL recognition/lysis of H2b target cells. The mechanism of epitope presentation is by the "natural" endogenous route, and appears to direct lysis as effectively as wild-type virus infection, in which the epitope is part of a 236 residue glycoprotein.

Genetic regulation of class I major histocompatibility complex (MHC) antigen induction on astrocytes

Neural cells, including astrocytes, normally do not express detectable levels of class I major histocompatibility complex (MHC) molecules, unlike cells of most tissues. However, upon cultivation in vitro, astrocytes begin to express class I molecules, increasing with time after plating. This spontaneous expression was examined in the present study to characterize inducible expression on astrocytes among various strains of mice. Inducible expression, either as a consequence of cultivation or standard gamma-interferon treatment, differed markedly among the strains examined. Analysis of congenic strains on a C57BL/10 (B10) background showed that expression was controlled by genes within the MHC locus. Examination of additional congeneic animals with various recombinations within the MHC showed that high or low expression of MHC molecules correlates with the presence of particular MHC class I genes. In general, H-2a and H-2d class I products are expressed much higher on astrocytes than H-2b and H-2s products. This difference in expression is not seen on spleen cells indicating tissue specificity. Moreover, levels of expression at the cell surface are reflected by the steady-state level of RNA message within astrocytes of the different strains.

Persistence of rat parvovirus in athymic rats

Euthymic (SD or outbred rnu/+) and athymic (rnu/rnu) rats were inoculated oronasally or intraperitoneally with the RV-Y strain of rat virus when they were 2 days or 4 weeks old. Clinical signs of infection in athymic infants were similar to those in euthymic infants, but significantly more athymic infants died. Some infants developed anemia and thrombocytopenia. After inoculation of infants. RV-Y was detected in surviving euthymic rats for 7 weeks and in surviving athymic rats for at least 10 weeks. After oronasal inoculation of 4 week-old rats no clinical illness was observed. RV-Y persisted less than 6 weeks in juvenile euthymic rats but at least 12 weeks in athymic juvenile rats. Intraperitoneal inoculation of juveniles resulted in infection for at least 6 weeks. The antibody response of athymic rats to RV-Y was significantly reduced compared to that of euthymic rats. These studies indicate that T cell deficiency increases the severity and duration of RV infection and imply that T cells are required for the full expression of resistance to RV infection. They also suggest that RV-Y induced anemia could serve as a model for human parvovirus-induced anemia.

Borna disease, a progressive meningoencephalomyelitis as a model for CD4+ T cell-mediated immunopathology in the brain

A homogeneous T cell line NM1 with Borna disease (BD) virus reactivity could be established. The NM1 cells have been characterized as CD4+ T cells. Adoptive transfer revealed that this MHC class II-restricted immune cell is responsible for the immunopathological effect leading to BD, a progressive meningoencephalomyelitis.

T-cell-mediated clearance of mouse hepatitis virus strain JHM from the central nervous system

Clearance of the neurotropic JHM strain of mouse hepatitis virus from the central nervous system was examined by the transfer of spleen cells from immunized donors. A T cell with the surface phenotype of Thy1.2+ CD4+ CD8- asialo-GM1+ Mac-1- was found to be necessary for viral clearance. The surface phenotype and adherence to nylon wool suggest that these cells are activated helper-inducer T cells. Adoptive transfer to congenic histocompatibility strains demonstrated the necessity for compatibility at the D locus of the major histocompatibility complex. The expression of the CD4 surface marker and the requirement for major histocompatibility complex class I were further studied by the transfer of cells to recipients treated with anti-CD4 or anti-CD8 monoclonal antibodies. Treatment of recipients with either the anti-CD8 or the anti-CD4 antibodies inhibited virus clearance from the central nervous system. This suggests that the CD4+ cell acts as a helper and that virus is cleared from the central nervous system. This suggests that the CD4+ cell acts as a helper and that virus is cleared from the central nervous system by CD8+ cells that recognize viral antigen in the context of the H-2Db gene product.

Alloreactive cytotoxic T cells induce DNA fragmentation in peritoneal macrophages: evidence for target cell killing by cytotoxic T cells in vivo

This report addresses the question whether cytotoxic T cells can cause target cell death in vivo by examining target cell DNA fragmentation. The results show that alloreactive cytotoxic T cells induced significant DNA fragmentation in peritoneal macrophages in vivo and that the DNA fragment was a multiple of 180 +/- 30 bp. Furthermore, the effector cells which caused this characteristic DNA fragmentation were CD8+ T cells. These results demonstrate that cytotoxic T cells can cause target cell death in vivo.

In vivo expression of perforin by CD8+ lymphocytes during an acute viral infection

CTL and NK cells cultured in vitro have been shown to contain a cytolytic pore-forming protein (PFP/perforin/cytolysin). To date, it has not been determined whether perforin is expressed by CTL that have been primed in vivo. Here, we have infected mice with two strains of lymphocytic choriomeningitis virus (LCMV), one of which mainly produces choriomeningitis and, the other, hepatitis. Brain and liver cryostat sections obtained from LCMV-infected mice were stained for various lymphocyte markers, including perforin. We were able to detect a large accumulation of perforin antigen in CD8+/Thy-1+/asialo GM1+/CD4- lymphocytes, which in fact represent the main infiltrating cell type found in brain and liver sections obtained during the late acute stage of LCMV infection. Perforin was also detected in a smaller population of CD8-/asialo GM1+/NK 1.1+/F480- cells, presumably corresponding to NK cells. Perforin-positive cells were found to have the morphology of blasts or large granular lymphocytes (LGL). These observations, together with in vitro studies performed in the past, indicate that perforin may be associated exclusively with LGL-like CTL blasts and NK cells. Our results demonstrate for the first time the presence of perforin in CTL that have been primed in vivo and suggest that perforin-positive CTL may be directly involved in producing the immunopathology associated with the LCMV infection.

T cell memory. Long-term persistence of virus-specific cytotoxic T cells

This study documents that virus-specific CTL can persist indefinitely in vivo. This was accomplished by transferring Thy-1.1 T cells into Thy-1.2 recipient mice to specifically identify the donor T cell population and to characterize its antigenic specificity and function by using a virus-specific CTL assay. Thy-1.1+ T cells from mice previously immunized with lymphocytic choriomeningitis virus (LCMV) were transferred into Thy-1.2 mice persistently infected with LCMV. The transferred LCMV-specific CTL (Thy-1.1+ CD8+) eliminate virus from the chronically infected carriers and persist in the recipient mice in small numbers, comprising only a minor fraction of the total T cells. Upon re-exposure to virus, these long-lived "resting" CD8+ T cells proliferate in vivo to become the predominant cell population. These donor CD8+ T cells can be recovered up to a year post-transfer and still retain antigenic specificity and biological function. They kill LCMV infected H-2-matched cells in vitro and can eliminate virus upon transfer into a second infected host. In addition, these long-lived CD8+ T cells appear not to be dependent on help from CD4+ T cells, since depletion of CD4+ T cells has minimal or no effect on their biological properties (proliferation, CTL response, viral clearance). These donor CTL also exhibit an immunodominance over the host-derived LCMV-specific CTL response. When both host and donor T cells are present, the donor CTL response is dominant over the potential CTL response of the cured carrier host. Taken together, these results suggest that virus-specific CTL can persist for the life span of the host as memory cells.

Immune response in deep cervical lymph nodes and spleen in the mouse after antigen deposition in different intracerebral sites

Brain interstitial and cerebrospinal fluid drainage into the lymphatics was studied by injections of 5 microliters of packed sheep red blood cells (SRBC) injected into the caudate nucleus, the occipital lobe, and the lateral ventricle of the brain in mice. The number of plaque-forming cells (PFC) was determined in the deep cervical lymph nodes, the axillary lymph nodes, and the spleen, and the number of PFC was compared with the response in the same tissues after intravenous immunization with 0.1 ml 10% SRBC. The weight of the deep cervical lymph nodes increased 3.0 times on day 3 after injection in the brain parenchyma compared with the weight of these nodes after intravenous immunization. The antigen-specific response peaked on day 5, 392 +/- 37 PFC/10(6) for IgG in the deep cervical lymph nodes after antigen deposition in the caudate nucleus, whereas only a minor peak in the antigen-specific response was obtained after intraventricular antigen deposition, 127 +/- 79 PFC x 10(6) for IgG on day 6. There were no increased PFC in any of the lymph nodes after intravenous immunization. The experiments show an antigen-specific response in the deep cervical lymph nodes after intracerebral antigen deposition, whereas antigens deposited in the lateral ventricles drain preferentially to the blood, with a high response in the spleen.

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.

Fine dissection of a nine amino acid glycoprotein epitope, a major determinant recognized by lymphocytic choriomeningitis virus-specific class I-restricted H-2Db cytotoxic T lymphocytes

We define a nine-amino acid (aa) sequence of VAL-GLU-ASN-PRO-GLY-GLY-TYR-CYS-LEU as a major epitope for immunologic recognition of lymphocytic choriomeningitis virus (LCMV) by H-2b-restricted CTL. The epitope was characterized using molecular genetics to bracket broadly and chemistry to precisely identify aa residues 278-286 of the viral glycoprotein. The epitope's composition is characteristic of a reverse (beta turn) but not an amphipathic alpha helix. A series of peptides with a single aa substitution in position 278 of VAL with other nonpolar (hydrophobic) amino acids (LEU, ILE, ALA, or GLY) coat targets that are recognized and lysed by CTL clones recognizing this epitope. In contrast, substitution of VAL with either large aromatic amino acids (that add bulk: PHE, TYR) or polar side chains (SER, THR) segregates CTL clones normally recognizing aa 278-286 into two groups, one that remains lytic (permissive) despite these changes and another that fails to lyse, indicating CTL can discriminate at a single aa. A change in charge at this position (VAL----ASP or GLU), in general, reduces CTL lysis while a change of VAL to LYS or ASN has minimal affect for four of the five CTL clones analyzed. CTL reactivity with the viral epitope is restricted by the Db but not the Kb of the murine MHC haplotype. A 16-aa peptide of Db that spans alpha 1 residues 37-52 blocks CTL lysis, whereas the corresponding Kb peptide that differs from Db in a single aa in position 50 does not.

T4+ T helper cell function in vivo: differential requirement for induction of antiviral cytotoxic T-cell and antibody responses

This study documents the differential requirements of T4+ T helper cells in the induction of virus-specific cytotoxic T-lymphocyte (CTL) and antibody responses during acute lymphocytic choriomeningitis virus infection. Two monoclonal antibodies (GK1.5 and RL172.4) directed against the L3T4 (T4) molecule were used for depleting T helper cells from mice. Depletion of T4+ cells caused a pronounced suppression of antiviral antibody response (20-fold decrease) but had minimal effect on virus-specific CTL response (less than 2-fold reduction). Despite the elimination of greater than 90% of T helper cells, anti-L3T4-treated mice were able to generate a CTL response of sufficient magnitude to control the viral infection. In contrast, depletion of Lyt2+ T cells abrogated the CTL response and the ability to eliminate virus. Thus, our results underscore the importance of the Lyt2+ T-cell subset in controlling infection with this virus and show that a deficiency of T4+ T cells is likely to have a more severe effect on antibody production than on CTL responses.

Virus-lymphocyte interactions. III. Biologic parameters of a virus variant that fails to generate CTL and establishes persistent infection in immunocompetent hosts

Viruses that cause in vivo persistent infections avoid the host's immunologic surveillance machinery. A major component of that armamentarium is virus-specific MHC-restricted cytotoxic T lymphocyte (CTL) response of the host. Studies with lymphocytic choriomeningitis virus (LCMV) have uncovered a parental virus (CTL+) that in immuno-competent adults induces CTL and terminates acute infection and a variant (CTL-) that fails to elicit CTL responses and establishes a persistent state (R. Ahmed et al. (1984) J. Exp. Med. 160, 521-540). The biologic properties, similarities, and differences between CTL+ and CTL- viruses as regards their interactions with lymphocytes of newborn and adult mice is recorded here. CTL+ and CTL- viruses persist in lymphocytes of newborn inoculated mice, primarily within the T helper subset. Approximately 2% of lymphocytes express viral nucleic acid sequences while only 0.04% score as infectious centers suggesting incomplete viral replication. These levels were maintained over the course of infectious. In contrast, CTL- virus but not CTL+ persists in lymphocytes of mice inoculated when adults. Lymphocytes easily scored as infecting centers but rarely displayed nucleic acid sequences suggesting a different balance of incomplete to complete virion replication. Further, infectious centers decreased by 10-fold from the 3rd to 68th day of infection and the total numbers of T lymphocytes in the circulation decreased suggesting CTL- may replicate in and destroy lymphocytes of adult mice. In the following paper the primary nucleotide structure of the LCMV small RNA segment, the segment responsible for generation of CTL and encoding the proteins recognized by CTL, for CTL+ and CTL- viruses is reported.

T-cell tolerance: exposure to virus in utero does not cause a permanent deletion of specific T cells

This study documents the curing of a congenitally acquired chronic viral infection and the acquisition of T-cell competence by a previously tolerant host. Infection of mice with lymphocytic choriomeningitis virus (LCMV) is a classic model of viral persistence and antigen-specific T-cell unresponsiveness. Mice infected at birth or in utero become lifelong carriers with no detectable virus-specific cytotoxic T lymphocyte (CTL) responses. This chronic infection can be eliminated by adoptive transfer of Lyt-2+ T cells from LCMV-immune mice. To determine whether these cured carriers were capable of generating their own LCMV-specific CTL response, mice congenic at the Thy-1 locus (Thy-1.1 and Thy-1.2) were used in the adoptive transfer experiments. Host-derived T-cell responses were checked after treating the cured carriers with a monoclonal antibody to deplete the immune donor T cells. Such cured carrier mice were able to generate a host-derived virus-specific CTL response and resisted a second LCMV challenge in the absence of any donor T cells. In addition, bone marrow cells from these cured carriers could functionally reconstitute irradiated mice. Thus this report demonstrates the acquisition of LCMV-specific T-cell competence by previously unresponsive carrier mice infected in utero. These results show that exposure to a virus even during embryonic life does not cause a permanent deletion of specific T cells. These findings are of significance to the understanding of tolerance mechanisms and have implications for the treatment of chronic viral infections.

Molecular definition of a major cytotoxic T-lymphocyte epitope in the glycoprotein of lymphocytic choriomeningitis virus

Analyses with segmental reassortants of lymphocytic choriomeningitis virus (LCMV) RNA have shown that cytotoxic T lymphocytes (CTL) are induced by and recognize proteins encoded by the viral short segment, which specifies two virus structural proteins, glycoprotein (GP) and nucleoprotein (NP). Expression of cDNA copies of these genes in vaccinia virus vectors demonstrates that C57BL/6 (H2bb) mice mount significant CTL responses to both GP and NP. We have used LCMV-specific H2bb-restricted CTL clones and a family of serial C-terminal truncations of the LCMV GP expressed in vaccinia virus to map the precise specificities of the anti-GP clones. Of the 18 CTL clones studied, 1 recognizes NP and the other 17 recognize GP. The reactivities of 14 of the 17 anti-GP CTL clones against the deleted GP molecules have been fully characterized, and two clear patterns of anti-GP activity have emerged, defining at least two CTL epitopes. The first epitope, recognized by only two of the clones, lies within GP residues 1 to 218. The second is recognized by all 12 of the remaining clones and was mapped, by using the GP deletions, to a 22-amino-acid region comprising GP residues 272 to 293. A synthetic peptide representing this area sensitized uninfected syngeneic target cells to lysis both by bulk CTL obtained from the spleen after a primary immunization and by appropriate CTL clones. Two sets of criteria are available which are said to identify potential T-cell epitopes, one based on primary amino acid sequence and the second based on protein secondary structure. Neither of these predictive schemes would have identified region 272 to 293 as a CTL recognition motif, indicating that such programs are of limited usefulness as presently conceived. Analysis of the CTL clones shows clearly that all three families (anti-NP and anti-GP 1 to 218 and 272 to 293) direct efficient cross-reactive killing against a variety of serologically distinct strains of LCMV.

The secondary in vitro murine cytotoxic T cell response to the flavivirus, West Nile

A secondary in vitro murine cytotoxic response to the flavivirus, West Nile (WNV) is described. Cytotoxic activity was obtained from spleen cells of mice primed 7 days previously with 10(6) p.f.u. WNV and boosted in vitro for a further 5 days with WNV-infected stimulator spleen cells. The cells responsible for lysis of WNV-infected target cells were restricted by class 1 H-2 antigens. The K region of the H-2k haplotype and both the K and D regions of the H-2d haplotype were permissive. The cytotoxic cells were virus-specific with respect to WNV and Influenza. The phenotype of the cells which mediated cytotoxicity was Thy 1+, Lyt 2+ and L3T4-; however an L3T4+ helper population was required for the optimal generation of the cytotoxic response in vitro.

Selective acceptance of MHC class I-deficient tumor grafts in the brain

H-2-deficient (H-2-) tumor variants were accepted equally well compared with H-2+ wild-type cells in the brain of syngeneic mice, while the H-2- cells were selectively eliminated when inoculated extracranially. This indicates a specific absence or suppression of the defense against MHC class I-deficient cells in the brain, suggested to be mediated by NK cells. In contrast, T cell-mediated immune reactions could clearly be detected in the brain under the same experimental conditions. This was shown in control experiments where H-2+ tumor cells were rejected from the brain of preimmunized or allogeneic mice. The present findings may be important for the understanding of neurotropic virus infections, immunology and immunotherapy of brain tumors, as well as for the growing interest in tissue grafting within the central nervous system.

Prevention of type I diabetes in nonobese diabetic mice by virus infection

The nonobese diabetic (NOD) mouse is an animal model of type I diabetes and develops a characteristic autoimmune lesion in the islets of Langerhans with lymphocytic infiltration and destruction of pancreatic beta cells. The result is hypoinsulinemia, hyperglycemia, ketoacidosis, and death. Diabetes usually begins by the sixth month of age but can occur earlier when young NOD mice are infused with lymphocytes from older NOD donors. When newborn or adult NOD mice were infected with a lymphotropic virus they did not become diabetic. The interaction between viruses and lymphocytes is pivotal in aborting diabetes, as established by experiments in which lymphocytes from virus-infected donors failed to transfer diabetes. In contrast, lymphocytes from age- and sex-matched uninfected donors caused disease. Therefore, viruses and, presumably, their products can be developed to be beneficial and may have potential as a component for treatment of human diseases. Further, these results point to the utility of viruses as probes for dissecting the pathogenesis of a nonviral disease.

Immune therapy of a persistent and disseminated viral infection

The mechanism of viral clearance was studied by using the mouse model of chronic infection with lymphocytic choriomeningitis virus. Distinct patterns of viral clearance and histopathology were observed in different organs after adoptive immune therapy of persistently infected (carrier) mice. Clearance from the liver occurred within 30 days and was accompanied by extensive mononuclear cell infiltrates and necrosis of hepatocytes. Infectious virus and viral antigen were eliminated concurrently. This pattern of viral clearance was also seen in most other tissues (i.e., lung, spleen, lymph nodes, pancreas, etc.). In contrast, a different pattern of clearance was observed in the brain. Infectious virus was eliminated within 30 days, but viral antigen persisted in the central nervous systems of treated carrier mice for up to 90 days. The urinary system was the most resistant to immune therapy. Elimination of infectious virus and viral antigen from the kidney took greater than 200 days and even then was not complete; trace levels of infectious virus were still present in the kidneys of some treated carrier mice. After immune therapy, viral antigen in the kidney was located within renal tubules that costained for intracellular mouse immunoglobulin G. This unusual staining pattern, coupled with the observation of large numbers of plasma cells within the kidney, suggests that virus-immunoglobulin G complexes found in the tubules may represent in situ immune complex formation as opposed to deposition of circulating immune complexes. In conclusion, these results suggest that the site (organ) of viral persistence is an important consideration in developing treatment strategies for controlling chronic viral infections.

Effective clearance of a persistent viral infection requires cooperation between virus-specific Lyt2+ T cells and nonspecific bone marrow-derived cells

The lifelong chronic lymphocytic choriomeningitis virus (LCMV) infection established in neonatally or congenitally infected mice can be eliminated by adoptive transfer of lymphoid cells from LCMV-immune mice. In this study, we have identified the effector cells mediating the clearance of persistent and disseminated LCMV infection. Using mice that are recombinant in the H-2 region and by selective depletion of lymphocyte subpopulations, we show that viral clearance was mediated by LCMV-specific Lyt2+ L3T4- T cells that are restricted to the class I genes of the major histocompatibility complex. In addition, our results show a requirement for host-derived bone marrow cells for the effective elimination of virus from the liver. These studies emphasize the importance of virus-specific T cells and an intact bone marrow function in viral clearance.

Cell-mediated cytotoxic response to respiratory syncytial virus in infants with bronchiolitis

A cell-mediated cytotoxic response to respiratory syncytial (RSV) was demonstrated in the peripheral blood of 4 of 22 infants with acute bronchiolitis. These 4 infants were aged 3 weeks to 3 months. No such response was found in infants older than 4 months. All 4 infants with a positive response had mild infections.

CD8-positive T lymphocytes specific for murine cytomegalovirus immediate-early antigens mediate protective immunity

We have shown in a murine model system for acute, lethal cytomegalovirus (CMV) disease in the immunocompromised natural host that control of virus multiplication in tissues, protection from virus-caused tissue destruction, and survival are mediated by virus-specific CD8+ CD4-T lymphocytes. Protection from a lethal course of disease did not result in a rapid establishment of virus latency, but led to a long-lasting, persistent state of infection. The CD8- CD4+ subset of T lymphocytes was not effective by itself in controlling murine CMV (MCMV) multiplication in tissue or essential for the protective function of the CD8+ CD4- effector cells. The antiviral efficacy of the purified CD8+ CD4- subset was not impaired by preincubation with fibroblasts that presented viral structural antigens, but was significantly reduced after depletion of effector cells specific for the nonstructural immediate-early antigens of MCMV, which are specified by the first among a multitude of viral genes expressed during MCMV replication in permissive cells. Thus, MCMV disease provides the first example of a role for nonstructural herpesvirus immediate-early antigens in protective immunity.

Astrocyte gene expression in Creutzfeldt-Jakob disease

Gliosis (hyperplasia and hypertrophy of astrocytes), the fundamental response of the central nervous system to tissue destruction, typically becomes apparent only several weeks after injury. The biochemical hallmark of this response is a marked accumulation of the specific astrocyte intermediate filament glial fibrillary acidic protein (GFAP). To date despite its importance, the mechanisms of GFAP gene regulation have not been studied in any developmental or pathological system to our knowledge, and the molecular signals for GFAP mRNA and protein accumulation are not defined. In Creutzfeldt-Jakob disease, a progressive dementing illness caused by an "unconventional agent," we find steadily increasing elevations of GFAP mRNA throughout the later stages of disease, using two independent GFAP cDNA clones, representing the entire insert or the 3'-noncoding region (pScr-1). The accumulation of GFAP, assessed immunocytochemically, follows GFAP mRNA elevation. A 5-fold stimulation of GFAP gene expression precedes the development of florid histologic lesions in the cerebrum, and in the cerebellum 5- to 6-fold increases occurred with no detectable spongiform changes at any time during disease. Therefore, these GFAP changes cannot be simply a response to neuronal damage. These effects are directly or indirectly caused by high local concentrations of agent and possibly involve a humoral factor.

Prediction of antigenic determinants and secondary structures of the major AIDS virus proteins

Criteria for the design of peptide vaccines to prevent AIDS are presented. The best vaccine candidates contain both B and T lymphocyte-defined epitopes in regions conserved in sequence between viral isolates. We propose that attention should focus on proteins specified by the gag and, possibly, pol genes in addition to the env gene envelope glycoproteins being actively studied. The predictions of B- and T-epitopes are refined by consideration of secondary structure prediction and inter-isolate sequence variability to suggest peptides from env, gag and pol that would be the best vaccine candidates.

Mechanism of recovery from acute virus infection: treatment of lymphocytic choriomeningitis virus-infected mice with monoclonal antibodies reveals that Lyt-2+ T lymphocytes mediate clearance of virus and regulate the antiviral antibody response

After intravenous infection of mice, lymphocytic choriomeningitis virus multiplied in spleens and livers, attaining highest concentrations on days 4 to 6. The subsequent clearance was as rapid, and 8 to 10 days after inoculation, infectivity was usually below detectability. During the effector phase of virus elimination, both cytotoxic T-cell (CTL) activity and the number of cells producing antiviral antibodies were high. Monoclonal antibodies directed against T lymphocytes and T-lymphocyte subsets were inoculated once intravenously 5, 6, or 7 days after infection of the animals, and the effects on antiviral immune responses, as well as on elimination of virus from the organs, were determined. Treatment with anti-Thy-1 and anti-Lyt-2 antibodies blocked elimination of the virus and profoundly diminished the activity of spleen CTLs but reduced the antibody response partially (anti-Thy-1) or increased it (anti-Lyt-2). In contrast, treatment with the anti-L3T4 antibody had essentially no effect on either virus elimination or CTL response but abolished antibody production. We conclude that Lyt-2+ (cytotoxic-suppressive) T lymphocytes are needed for elimination of the virus and also regulate the humoral response but that antiviral antibodies are not essential for control of the infection.