Inhibitory role of neutrophils on influenza virus multiplication in the lungs of mice.

The protective role of neutrophils on intranasal infection of influenza virus was investigated in 3 strains of tumor-bearing mice with neutrophilic leukocytosis. In vitro multiplication of influenza virus was inhibited by neutrophils from both normal and tumor-bearing mice, and the inhibitory effect of neutrophils was augmented by an addition of fMLP to the culture. Pulmonary virus infectivities in the early phase after infection decreased in such ICR and BALB/c mice, and virus elimination in the late phase was accelerated in the ICR mice. However, no decrease in pulmonary virus infectivity was observed in tumor-bearing C57BL/6 mice. Intranasal administration of fMLP into normal and tumor-bearing C57BL/6 mice after infection significantly inhibited the virus propagation in the lungs. The decrease in neutrophil infiltration into the lung in tumor-bearing C57BL/6 mice was confirmed from histological observations of the lung and lung lavage after infection and from analysis of the neutrophil chemotactic activity induced by fMLP. This might be responsible for the high level of pulmonary virus titer in tumor-bearing C57BL/6 mice. Phagocytic activities of alveolar macrophages and productions of neutralizing antibody were suppressed in the 3 strains of tumor-bearing mice. These observations indicated that neutrophils could be significant effector cells as a host defense mechanism against influenza virus infection in vivo, and infiltration and functional activation of neutrophils could play a significant role in virus elimination from the infected site. Furthermore, the inhibition of virus propagation by neutrophils in vitro was almost completely abrogated by an addition of ZnSO4, suggesting that calprotectin could inhibit influenza virus multiplication.     

Depression of early protection against influenza virus infection by cyclophosphamide and its restoration by Y-19995 [2,4'-bis(1-methyl-2-dimethyl-aminoethoxyl)-3-benzoylpyridine dimaleate

The relationship between depression of early protection against influenza virus infection and the decrease in the number of peripheral polymorphonuclear leukocytes in cyclophosphamide-treated mice was investigated by means of a novel synthetic compound, Y-19995 [2,4'-bis(1-methyl-2-dimethyl-aminoethoxyl)-3-benzoylpyridine dimaleate], which had been shown to exert a potent restorative effect on leukocytopenia in immunocompromised hosts. Following intranasal inoculation with influenza virus (1.5 x 10(3) plaque-forming units) into untreated mice, the pulmonary virus titer progressively increased during 3 days and decreased gradually from day 7 after infection. The treatment with cyclophosphamide 2 days before infection markedly enhanced the pulmonary virus multiplication from the early phase of infection, and the higher virus titer was maintained thereafter. When mice were given Y-19995 after cyclophosphamide treatment, virus titers from the early to late phases of infection were lower than those in untreated mice. The number of peripheral polymorphonuclear leukocytes in cyclophosphamide-treated mice rapidly decreased and returned to normal levels only 9 days after the treatment, while such leukocytopenia was prevented to some extent and the leukocyte count was restored completely up to 7 days by postcyclophosphamide treatment with Y-19995. Furthermore, the treatment with Y-19995 augmented the inactivation of virus by the polymorphonuclear leukocytes. However, the virus inactivation by alveolar macrophages was modified only slightly by Y-19995 treatment. In addition, Y-19995 treatment could potentiate antibody-dependent cell-mediated cytotoxicity of polymorphonuclear leukocytes against the virus-infected target cells, and the production of serum neutralizing antibody to influenza virus in untreated and cyclophosphamide-treated mice. Y-19995 revealed neither antiviral nor interferon-inducing activities.(ABSTRACT TRUNCATED AT 250 WORDS)     

Natural killer cell depletion enhances virus synthesis and virus-induced hepatitis in vivo

The role of natural killer (NK) cells in the natural resistance of mice to infections by several viruses was examined. Mice were specifically depleted of NK cells by i.v. injection of rabbit antiserum to asialo GM1, a neutral glycosphingolipid present at high concentrations on the surface of NK cells. Control mice were left untreated or were injected with normal rabbit serum. Four to 6 hr later, these mice were infected with lymphocytic choriomeningitis virus (LCMV), mouse hepatitis virus (MHV), murine cytomegalovirus (MCMV), or vaccinia virus. The mice were sacrificed 3 days post-infection and assayed for virus in liver and spleen, spleen NK cell activity, and plasma interferon (IFN). All mice treated with anti-asialo GM1 antibody had drastically reduced NK cell-mediated lysis. Correlating with NK cell depletion, these mice had significantly higher (up to 500-fold) titers of MCMV, MHV, or vaccinia virus in their livers and spleens as compared to control mice. NK cell-depleted MCMV and MHV-infected mice had higher levels of plasma IFN than controls, correlating with the higher virus titers. These NK cell-depleted, virus-infected mice had more extensive hepatitis, assayed by the number of inflammatory foci in their livers, as compared to control virus-infected mice; these foci were also larger and contained more degenerating liver cells than those in control mice. In contrast to the results obtained with MHV, MCMV, and vaccinia virus, NK cell depletion had no effect on virus titers in the early stages of acute LCMV infection or during persistent LCMV infection. Mice depleted of NK cells had similar amounts of LCMV in their spleens and similar plasma IFN levels. Because this antibody to asialo GM1 does not impair other detectable immunologic mechanisms, these data support the hypothesis that NK cells act as a natural resistance mechanism to a number of virus infections, but suggest that their relative importance may vary from virus to virus.     

Anti-glomerular basement membrane antibody-induced experimental glomerulonephritis: evidence for dose-dependent, direct antibody and complement-induced, cell-independent injury

The immunopathogenesis of anti-glomerular basement membrane antibody-induced glomerulonephritis (anti-GBM-GN) involves the triad of antibody fixation to the glomerular basement membrane, local complement activation and polymorphonuclear leucocyte (PMN) infiltration. We sought to investigate the potential for contributions to renal injury from each component of this triad (i.e., antibody, complement, and PMN). This study compares the ability of antibody to induce injury in normal, PMN-depleted and dual (i.e., PMN + complement)-depleted rabbits by assessing the quantity of kidney-fixed antibody (KFA) necessary to induce proteinuria. (The KFA levels are expressed in micrograms of antibody bound per gram renal cortex.) Normal animals developed significant proteinuria at KFA 60 +/- 6 micrograms/g. PMN-depleted animals were injury free at KFA 60 +/- 6 micrograms/g, but developed heavy proteinuria at KFA 140 +/- 5 micrograms/g. The protection from injury by PMN depletion at lower KFA levels confirms the important contribution of PMN to injury in this model. Furthermore, the demonstration of a clearcut threshold for injury despite PMN-depletion indicates that glomerular antibody deposition and complement activation can cause direct PMN-independent injury. Dual depletion studies showed a significantly higher KFA threshold for injury in PMN + complement-depleted animals than in PMN-depleted, complement intact animals (195 +/- 10 micrograms/g, cf. 140 +/- 5 micrograms/g; p less than 0.01). The occurrence of injury despite dual mediator depletion demonstrates that antibody itself can produce direct, complement and PMN independent renal injury. Together the PMN depletion and dual depletion studies indicate that antibody-induced glomerular complement activation produces direct, PMN-independent renal injury that can be prevented by complement depletion. Thus each of the potential mediators studied is individually capable of producing renal injury in anti-GBM-GN. In addition to the well established injurious role of PMN, this study demonstrates that glomerular complement activation and anti-GBM antibody deposition may both produce neutrophil-independent components of renal injury. The relative contributions of the individual mediators to injury is dependent on the quantity of antibody deposited within the glomerulus.     

Persistent infection with mouse hepatitis virus of low virulence in nude mice.

A persisting type of infection with wasting syndrome was established in congenitally athymic nude mice after intraperitoneal inoculation with a mouse hepatitis virus which was not fully pathogenic for heterozygous haired littermates. From the liver, spleen, lymph nodes, and brain of most infected nude mice, the virus was detected at high titers during aperiod from 6 to 35 days postinfection, occurrence of degenerative and necrotic lesions being correlated with virus titers in these organs. The titer of serum neutralizing antibody remained undetectable or very low in most diseases nude mice, whereas some animals resisting the infection could produce antibody at a later stage. In heterozygous haired mice, some lesions were detectable at a very early stage of infection in the spleen and liver, but they seemed to disappear with a marked elevation of the neutralizing antibody titer. Nude mice were able to resist the virus infection when they had previously received transfer of thymocytes from weanling heterozygous littermates.     

Defense mechanisms against primary influenza virus infection in mice. I. The roles of interferon and neutralizing antibodies and thymus dependence of interferon and antibody production.

To investigate the defensive roles and production of interferon and antibodies, C3H/He mice were subjected to various immunosuppressive treatments and infected with influenza virus. In infected normal control mice the pattern of pulmonary viral growth can be divided into three phases. The first phase is characterized by an exponential increase of virus titer, the second by a rapid decrease, and the third by a moderate decrease. At the time of transition from the first phase to the second in pulmonary virus growth, interferon could be detected in the tracheobronchial washings of infected mice, but neutralizing antibodies could not. In infected B cell-deprived mice and infected anti-mu-treated mice, the transition from the first phase to the second occurred without any detectable antibody production, and interferon could be induced in the early stage of infection. However, the pulmonary virus in these mice increased again exponentially until the death of the mice. In infected T cell-deprived mice which could not induce interferon, but produced IgM-neutralizing antibodies, the second phase was not observed after the first phase, but a transient plateau phase could be demonstrated, and then the pulmonary virus increased again exponentially until the death of the mice. In anti-gamma-treated infected mice, pulmonary virus growth and production of interferon and neutralizing antibody were almost similar to those of infected normal control mice except for the absence of IgG neutralizing antibody production. Although anti-alpha-treated infected mice produced interferon and no IgA antibody, the transition from the first exponential increase of pulmonary virus to the second rapid decrease was seen, but then the virus increased exponentially again until the death of the mice. These results suggest that interferon plays an important role in the transition from the first phase to the second, and that T cells are required for interferon induction in mice infected with influenza virus. These data also suggest that IgA antibodies play an important role in the inhibition of virus propagation in the lungs after the disappearance of interferon. Moreover, infected T cell-deprived mice could produce only IgM neutralizing antibodies, but not IgG and IgA antibodies. Therefore, T cells are required for the production of IgG and IgA antibodies and even     

Protective Effects of Specific Immunity to Viral Neuraminidase on Influenza Virus Infection of Mice

Antibody specific for viral neuraminidase can be demonstrated in mice following (i) pulmonary infection with influenza virus, (ii) immunization with ultraviolet-in-activated influenza virus, (iii) immunization with isolated neuraminidase of influenza A(2) virus, and (iv) passive immunization with sera of rabbits immunized with isolated A(2) neuraminidase. Neuraminidase antibody produced by any of these methods exerts a profound inhibiting effect on virus replication in the lungs of mice challenged with strains of virus having homologous neuraminidase protein, even in the absence of hemagglutinating inhibiting antibody to the challenge virus, and results in markedly decreased pulmonary virus titers and diminished lung lesions. These observations suggest that antineuraminidase immunity may play a significant role in the protection against influenza virus challenge observed in mice after infection or artificial immunization.     

Dissociation between alveolar transmigration of neutrophils and lung injury in hyperoxia

The objective of this study was to quantitatively assess changes in cell adhesion molecule (CAM) expression on the pulmonary endothelial surface during hyperoxia and to assess the functional significance of those changes on cellular trafficking and development of oxygen-induced lung injury. Mice were placed in >95% O(2) for 0-72 h, and pulmonary injury and neutrophil (PMN) sequestration were assessed. Specific pulmonary CAM expression was quantified with a dual-radiolabeled MAb technique. To test the role of CAMs in PMN trafficking during hyperoxia, blocking MAbs to murine P-selectin, ICAM-1, or platelet-endothelial cell adhesion molecule-1 (PECAM-1) were injected in wild-type mice. Mice genetically deficient in these CAMs and PMN-depleted mice were also evaluated. PMN sequestration occurred within 8 h of hyperoxia, although alveolar emigration occurred later (between 48 and 72 h), coincident with rapid escalation of the lung injury. Hyperoxia significantly increased pulmonary uptake of radiolabeled antibodies to P-selectin, ICAM-1, and PECAM-1, reflecting an increase in their level on pulmonary endothelium and possibly sequestered blood cells. Although both anti-PECAM-1 and anti-ICAM-1 antibodies suppressed PMN alveolar influx in wild-type mice, only mice genetically deficient in PECAM-1 showed PMN influx suppression. Neither CAM blockade, nor genetic deficiency, nor PMN depletion attenuated lung injury. We conclude that early pulmonary PMN retention during hyperoxia is not temporally associated with an increase in endothelial CAMs; however, subsequent PMN emigration into the alveolar space may be supported by PECAM-1 and ICAM-1. Blocking PMN recruitment did not prevent lung injury, supporting dissociation between PMN infiltration and lung injury during hyperoxia in mice.     

Non-antibody-mediated control of parasitemia in acute experimental Chagas' disease

There appear to be two phases in the control of parasitemia in acute Chagas' disease in the mouse. The first phase occurs during the first few weeks after infection and control is achieved through a thymus-dependent, antibody-independent mechanism. Challenge of B cell-suppressed C3H and F1 (C57BL/6 X C3H) mice with the Brazil strain of Trypanosoma cruzi led to a course of parasitemia for the first 3 wk after infection similar to that seen in normal C3H or F1 mice and markedly lower than the parasite levels observed in the blood of nu/nu mice. Challenge of BXH-2 recombinant inbred mice resulted in a course of parasitemia similar to that seen in nu/nu mice up to day 16 despite the production of normal levels of antibody. The BXH-2 mice lack the ability to effect the early control of parasitemia. The second phase begins several weeks after infection with the rise in antibody titer, and the control is exerted through an antibody-mediated mechanism. In all B cell-suppressed mice, an inexorable rise in parasitemia occurred up to the time of death, which suggests that antibody is important for the eventual clearance of parasites from the blood. A comparison of the IgM and IgG antibody titers to T. cruzi in a series of resistant and susceptible strains showed that there was no correlation between the appearance of specific antibody or antibody titers and the levels of parasitemia observed. The level of parasitemia attained in the late acute phase may be primarily determined by the extent of parasite proliferation in the early acute phase.     

Passive transfer of local immunity to influenza virus infection by IgA antibody

Secretory IgA is presumed to be the mediator of mucosal immunity based on many studies that show a correlation between protection and secretory IgA titers; however, a causal relationship has not yet been established. Classically, passive transfer of antibody has been used to demonstrate causality, but the passive transfer of local immunity with physiologically transported IgA has not been previously reported. In this study mice were injected intravenously with polymeric IgA (pIgA), monomeric IgA (mIgA), or IgG1 mAb specific for the H1 hemaglutinin of PR8 influenza virus. pIgA was shown to be specifically transported into nasal secretions relative to the mIg. The transported pIgA was functional, as evidenced by its ability to bind to virus in an ELISA assay and to protect nonimmune mice against intranasal infection with H1N1 but not H3N2 influenza virus. Intravenous injection of similar virus-neutralizing doses of anti-influenza IgG1 mAb did not protect against nasal viral challenge. IgA-mediated protection could be abrogated by the intranasal administration of antiserum against the alpha chain of IgA. These data demonstrate the passive transfer of local immunity by the i.v. administration of pIgA antibody and show that the IgA in secretions can protect against influenza virus infection. This general approach could provide a model for the evaluation of the role of local IgA in host defense against other pathogens.     

Alveolar macrophages regulate the induction of primary cytotoxic T-lymphocyte responses during influenza virus infection.

Virus-specific cytotoxic T lymphocytes (CTL) are thought to be responsible for the eradication of respiratory influenza virus infections by direct cytolysis of virus-infected epithelial cells. In this study, we provide evidence for a role for alveolar macrophages (AM) in the regulation of pulmonary virus-specific CTL responses. Prior to infection with influenza virus, AM were selectively eliminated in vivo with a liposome-mediated depletion technique, and virus-specific CTL activities of lung and mediastinal lymph node (MLN) cells were assayed ex vivo and compared with those for normal mice. AM depletion resulted in increased primary CTL responses and changed the kinetics of the CTL response. Flow cytometric analysis of lung and MLN cells showed that the percentage of CD8+ cells was not altered after AM depletion and that lung cells from AM-depleted mice had an increased capacity to lyse virus-infected cells. Upon restimulation in vitro, virus-specific CTL activity in lung cells of normal mice was similar to that in lung cells of AM-depleted mice. Furthermore, elimination of AM resulted in increased virus titers in the lung, but virus clearance as a function of time was not affected. Our results show that AM regulate virus-specific CTL responses during respiratory influenza virus infection by removing viral particles, by downregulating the priming and activity of CTL in MLN cells, and by inhibiting the expansion of virus-specific CTL in the lung.     

Survival of athymic (nu/nu) mice after Theiler''s murine encephalomyelitis virus infection by passive administration of neutralizing monoclonal antibody.

Little or no antiviral immune response is mounted in athymic nude mice infected with the Daniels strain of Theiler's murine encephalomyelitis virus. In these athymic mice, increasing levels of infectious virus could be detected in the central nervous system. Seventy-five percent (9 of 12) of the nude mice were moribund or dead by 4 weeks postinfection. In contrast, treatment of Theiler's virus-infected nude mice with a neutralizing monoclonal antibody (H7-2) against the viral protein VP-1 resulted in a dramatic reduction of infectious virus within the central nervous system. All antibody-treated nude animals survived beyond 4 weeks postinfection. Monoclonal antibody titers could be maintained by passive transfer in treated nude mice at levels comparable to those of polyclonal antibody titers found in heterozygous infected nu/+ littermates. Areas of demyelination were detected in the untreated animals as early as 7 days after infection with little or no remyelination present. In approximately one-half of the antibody-treated nude animals, no demyelinating lesions were found. However, the rest of these treated mice were found to have areas of both demyelination and remyelination. Thus, anti-Theiler's murine encephalomyelitis virus antibody against VP-1 can play a dramatic role in the survival of mice, clearance of virus, limiting viral spread, and altering the pattern of disease in the absence of a functional T-cell response.     

In vivo treatment of mice and hamsters with antibodies to asialo GM1 increases morbidity and mortality to pulmonary influenza infection

The role of natural killer (NK) cells in host defenses against influenza virus infections in the lung was investigated by using rabbit antiserum to asialo GM1 (RAGM1), a neutral glycosphingolipid expressed on the plasma membrane of NK cells and some mouse pulmonary macrophages. Intravenous or intratracheal (i.t.) administration of RAGM1 resulted in depletion of the (in vitro) NK activity in lung and spleen or lung alone, respectively. The NK activity was depleted as early as 12 hr post-inoculation of antiserum, but returned to the normal range of activity by 4 days after antibody administration. RAGM1 serum treatment had no effect on the cytotoxic macrophage activity expressed by the plastic-adherent mononuclear cell populations isolated from mouse or hamster lung. Treatment of mice or hamsters with an i.t. or i.v. inoculation of RAGM1 rendered both species of laboratory animals susceptible to increased morbidity and mortality during a pulmonary influenza infection. These data support the hypothesis that a population of NK cells exist in an extravascular compartment within the lung, and that this local population of NK cells in the lung is crucial to the early natural pulmonary defenses during influenza infection.     

Immunobiology of infection with recombinant vaccinia virus encoding murine IL-2. Mechanisms of rapid viral clearance in immunocompetent mice.

CD8+ cytotoxic T (Tc) lymphocytes mediate recovery from vaccinia virus (VV) infection. In mice, anti-VV Tc cells are detectable on or after day 3 after infection, and cytolytic activity peaks between days 5 and 6. A rVV encoding murine IL-2, VV-hemagglutinin (HA)-IL-2, was cleared more rapidly, compared with a control rVV, VV-HA-thymidine kinase (TK), from tissues of infected euthymic normal mice. The mechanism of VV-HA-IL-2 clearance was operative early in infection and correlated with an elevated NK cell response, before the induction of anti-VV Tc cell response. We have investigated the roles of NK cells, T cells, and IFN-gamma in the rapid clearance of VV-HA-IL-2, by using specific mAb. Depletion of NK cells with mAb significantly enhanced VV-HA-IL-2 but not VV-HA-TK titers 3 days after infection. NK cells alone could not account for rapid viral clearance, because VV-HA-IL-2 titers in NK cell-depleted mice were not comparable to VV-HA-TK titers. Treatment with a mAb to IFN-gamma completely abrogated the IL-2-induced mechanism(s) of VV-HA-IL-2 clearance, and titers of the IL-2-encoding virus were comparable to control virus titers. In addition, the elimination of CD4+ but not CD8+ T cells resulted in significant increases in VV-HA-IL-2 titers.     

Role of alveolar macrophage and migrating neutrophils in hemorrhage-induced priming for ALI subsequent to septic challenge

Acute lung injury (ALI) is identified with the targeting/sequestration of polymorphonuclear leukocytes (PMN) to the lung. Instrumental to PMN targeting are chemokines [e.g., macrophage inflammatory protein-2 (MIP-2), keratinocyte-derived chemokine (KC), etc.] produced by macrophage, PMN, and other resident pulmonary cells. However, the relative contribution of resident pulmonary macrophages as opposed to PMN in inducing ALI is poorly understood. We therefore hypothesize that depletion of peripheral blood PMN and/or the oblation of a macrophage-mediated PMN chemokine signal (via macrophage deficiency) will reduce the inflammation and ALI observed in mice following hemorrhage (Hem) and subsequent sepsis (CLP) in our murine model of ALI. To examine this we pretreated mice with either 500 microg anti-mouse Gr1 antibody/animal (to deplete PMN) or subjected mice deficient in mature macrophage (B6C3Fe-a/a-CsF1op) to Hem (90 min at 35 +/- 5 mmHg) followed by resuscitation. Twenty-four hours post-Hem, mice were subjected to CLP and killed 24 h later, and lung tissue samples were collected. Our data showed that in the absence of either peripheral blood PMN or mature tissue macrophages there was a suppression of IL-6, KC, and MIP-2 levels in lung tissue from Hem/CLP mice as well as a reduction in PMN influx to the lung and lung injury (bronchoalveolar lavage fluid protein). In contrast, lung tissue IL-10 and TNF-alpha levels were suppressed in the macrophage-deficient Hem/CLP mice compared with PMN-depleted Hem/CLP mice. Together, these data suggest that both the PMN and the macrophage are required to induce inflammation seen here, however, macrophage not PMN regulate the release of IL-10, independent of local changes in TNF.     

Effect of humoral immune responses on controlling viremia during primary infection of rhesus monkeys with simian immunodeficiency virus

Cellular immune responses mediated by CD8+ lymphocytes exert efficient control of virus replication during primary simian immunodeficiency virus (SIV) infection. However, the role that antibodies may play in the early control of virus replication remains unclear. To evaluate how antibody responses may affect virus replication during primary SIVmac infection, we depleted rhesus monkeys of B cells with anti-CD20 antibody. In normal rhesus monkeys immunized with tetanus toxoid, anti-CD20 treatment and resulting depletion of B cells inhibited the generation of antitetanus antibodies, while tetanus-specific T-cell responses were preserved. During the first 4 weeks after inoculation with SIVmac251, development of SIV-specific neutralizing antibody was delayed, and titers were significantly lower in B-cell-depleted monkeys than control-antibody-treated monkeys. Despite the lower neutralizing antibody titers, the levels of plasma SIV RNA and the linear slope of the decline seen in B-cell-depleted monkeys did not differ from that observed in monkeys treated with control antibody. However, beginning at day 28 after SIV infection, the B-cell-depleted monkeys showed a significant inverse correlation between neutralizing antibody titers and plasma virus level. These results suggest that the rapid decline of peak viremia that typically occurs during the first 3 weeks of infection was not significantly affected by SIV-specific antibodies. However, the inverse correlation between neutralizing antibodies and plasma virus level during the postacute phases of infection suggests that humoral immune responses may contribute to the control of SIV replication.     

The role of natural killer cells and interferon in resistance to acute infection of mice with herpes simplex virus type 1

The relative roles of interferon (IFN) and natural killer (NK) cells in herpes simplex virus type 1 (HSV-1) infection of mice were examined. Adoptive transfer of adult mouse leukocytes into 4- to 6-day-old suckling mice protected the recipients from HSV-1 infection, as judged by viral titers in the spleen 2 days postinfection. Protection was mediated by several classes of leukocytes, including those depleted of NK cell activity by antibody to asialo GM1 and those depleted of macrophages by size separation. Mice receiving these leukocytes produced significantly higher levels of IFN 6 hr postinfection (early IFN) than did HSV-1-infected mice not receiving donor leukocytes. Antibody to IFN, under conditions that blocked early but not late IFN synthesis, greatly enhanced HSV-1 synthesis in mice receiving leukocytes and completely removed the protective effect mediated by leukocytes. High doses of anti-asialo GM1 blocked both NK cell activity and early IFN production and resulted in high titers of HSV-1. This effect on virus synthesis was not seen if mice were given antibody 1 day postinfection. Lower doses of anti-asialo GM1, which still depleted NK cell activity but had no effect on early IFN production, did not enhance HSV-1 synthesis. Depletion of NK cell activity with a low dose of antibody had no effect on the reduced HSV-1 synthesis resulting from prophylactic IFN treatment or on the enhanced HSV-1 synthesis resulting from antibody to IFN treatment. Thus, resistance to acute HSV-1 infection in mice correlates with early IFN production but not with NK cell activity, suggesting that NK cells are not major mediators of natural resistance in this model and that the antiviral effect of IFN is not mediated by NK cells.     

Humoral immunity and protection of mice challenged with homotypic or heterotypic parvovirus.

BACKGROUND AND OBJECTIVES: Two serotypes of autonomously replicating parvoviruses infect laboratory mice. Genome regions coding for the nonstructural proteins of minute virus of mice [MVM] and mouse parvovirus [MPV] are almost identical, whereas capsid-coding sequences are divergent. We addressed these questions: Does humoral immunity confer protection from acute infection after challenge with homotypic or heterotypic parvovirus, and if it confers protection against acute MPV infection, does it also protect against persistent MPV infection? METHODS: Infant mice without maternal antibody or antibody to MVM or MPV and young adult mice given normal mouse serum or antibody to MVM or MPV were challenged with homotypic or heterotypic virus. In situ hybridization with target tissues was the indicator of infection. RESULTS: Humoral immunity failed to confer protection against acute heterotypic parvovirus infection. In passive transfer studies, MPV DNA was observed occasionally in lymph nodes, intestine, or the spleen of MPV-challenged mice given homotypic antibody and kept for 6 or 28 days. Variable proportions of mice given MPV antibody and homotypic challenge had viral DNA in lymphoid tissues 56 days after virus inoculation. CONCLUSION: A mouse or colony that has sustained infection with MVM or MPV is probably fully susceptible to infection with the heterotypic virus.     

The role of alpha/beta and gamma interferons in development of immunity to influenza A virus in mice

During influenza virus infection innate and adaptive immune defenses are activated to eliminate the virus and thereby bring about recovery from illness. Both arms of the adaptive immune system, antibody neutralization of free virus and termination of intracellular virus replication by antiviral cytotoxic T cells (CTLs), play pivotal roles in virus elimination and protection from disease. Innate cytokine responses, such as alpha/beta interferon (IFN-alpha/beta) or IFN-gamma, can have roles in determining the rate of virus replication in the initial stages of infection and in shaping the initial inflammatory and downstream adaptive immune responses. The effect of these cytokines on the replication of pneumotropic influenza A virus in the respiratory tract and in the regulation of adaptive antiviral immunity was examined after intranasal infection of mice with null mutations in receptors for IFN-alpha/beta, IFN-gamma, and both IFNs. Virus titers in the lungs of mice unable to respond to IFNs were not significantly different from congenic controls for both primary and secondary infection. Likewise the mice were comparably susceptible to X31 (H3N2) influenza virus infection. No significant disruption to the development of normal antiviral CTL or antibody responses was observed. In contrast, mice bearing the disrupted IFN-alpha/beta receptor exhibited accelerated kinetics and significantly higher levels of neutralizing antibody activity during primary or secondary heterosubtypic influenza virus infection. Thus, these observations reveal no significant contribution for IFN-controlled pathways in shaping acute or memory T-cell responses to pneumotropic influenza virus infection but do indicate some role for IFN-alpha/beta in the regulation of antibody responses. Recognizing the pivotal role of CTLs and antibody in virus clearance, it is reasonable to assume a redundancy in IFN-mediated antiviral effects in pulmonary influenza. However, IFN-alpha/beta seems to be a valid factor in determining tissue tropism and replicative rates of highly virulent influenza virus strains as reported previously by others, and this aspect is discussed here.