An analysis of effector T cell generation and function in mice exposed to influenza A or Sendai viruses

Analysis of Human RSV Immunity at the Molecular Level: Learning from the Past and Present

Human RSV is one of the most prevalent viral pathogens of early childhood for which no vaccine is available. Herein we provide an analysis of RSV epitope data to examine its application to vaccine design and development. Our objective was to provide an overview of antigenic coverage, identify critical antibody and T cell determinants, and then analyze the cumulative RSV epitope data from the standpoint of functional responses using a combinational approach to characterize antigenic structure and epitope location. A review of the cumulative data revealed, not surprisingly, that the vast majority of epitopes have been defined for the two major surface antigens, F and G. Antibody and T cell determinants have been reported from multiple hosts, including those from human subjects following natural infection, however human data represent a minority of the data. A structural analysis of the major surface antigen, F, showed that the majority of epitopes defined for functional antibodies (neutralizing and/or protective) were either shown to bind pre-F or to be accessible in both pre- and post-F forms. This finding may have has implications for on-going vaccine design and development. These interpretations are in agreement with previous work and can be applied in the larger context of functional epitopes on the F protein. It is our hope that this work will provide the basis for further RSV-specific epitope discovery and investigation into the nature of antigen conformation in immunogenicity.

Adverse events occurring after smallpox vaccination

We reviewed the literature on adverse events reported to occur after smallpox vaccination. Nearly one-half of the United States population is vaccinia-naïve and may be at risk for development of serious adverse events. We describe the clinical features of postvaccinial central nervous system disease, progressive vaccinia, eczema vaccinatum, accidental implantations, "generalized vaccinia," and the common erythematous and/or urticarial rashes. In the 1960s, death occurred approximately once in every million primary vaccinations, with fatalities resulting from progressive vaccinia, postvaccinial encephalitis, and eczema vaccinatum. Death in revaccinees occurred less commonly and almost entirely from progressive vaccinia. In today's population, death rates might be higher because of the increased prevalence of immune deficiency and atopic dermatitis.

Influenza virus-infected epithelial cells present viral antigens to antigen-specific CD8+ cytotoxic T lymphocytes

We have investigated the mechanisms involved in the clearance of viral infection at the epithelium level by analyzing the activity of influenza virus-specific cytotoxic T lymphocytes (CTL) against virus-infected CMT-93 intestinal epithelial cells. Epithelial cells infected with live influenza virus effectively present viral antigens and were lysed by both homotypic and heterotypic influenza virus-specific CD8+ T cells. These results shed new light on the control of viral infection through the elimination of virus-infected epithelial cells by virus-specific CTL and demonstrate that CMT-93 cells furnish an appropriate model for in vitro evaluation of CTL activity against virus-infected epithelial cells.

Cytotoxic T lymphocyte responses of infants after natural infection or immunization with live cold-recombinant or inactivated influenza A virus vaccine

The cytotoxic T lymphocyte (CTL) response of infants after immunization with either inactivated trivalent subvirion vaccine (TIV) or bivalent attenuated cold-recombinant (CR) vaccine or occurrence of natural influenza virus infection were compared in a blinded, placebo-controlled study during the 1987-1988 and 1988-1989 influenza epidemic seasons. Healthy infants between 6 and 13 months of age were randomly assigned and administered a single dose of intranasal bivalent (A/H3N2/A/H1N1) CR vaccine, a two-dose regimen of TIV (A/H3N2/A/H1N1/B) influenza vaccine, or placebo. Peripheral blood lymphocytes were obtained prior to and 2-8 weeks after vaccination and at the end of the epidemic season and stimulated with virus in vitro for 6 or 7 days. Lysis of autologous virus-infected target cells was assessed in a 4 hr 51Cr release assay. MHC class I-restricted influenza A-specific CTL was stimulated following natural influenza A virus infection but not after immunization with CR influenza A virus vaccine or TIV. These results demonstrate for the first time induction of influenza virus-specific CTL activity in infants under 1 year of age.

Varicella zoster virus-specific cytotoxicity following secondary immunization with live or killed vaccine

Subjects > or = 55 years of age were immunized with attenuated varicella zoster virus (VZV) vaccine (live) or with the same vaccine, which had been heated to 56 degrees C for 7 days (killed). The ability of subjects' blood lymphocytes to lyse target cells infected with VZV was determined before and 3 months after immunization using autologous Epstein-Barr virus (EBV) lymphoblasts as targets for human leukocyte antigen (HLA) class I restricted cytotoxicity and human fibroblasts as targets for unrestricted (natural killer [NK]) cytotoxicity. The live vaccine recipients showed an increase in their class I-restricted lysis of targets compared with the recipients of the killed vaccine. The two populations showed equivalent increase in their NK-dependent lysis of fibroblast targets. The results support the view that both the live and killed vaccines stimulate cytotoxicity by VZV-specific lymphocytes but that the live vaccine stimulates relatively more class I-restricted killing.

Influenza A subtype cross-protection after immunization of outbred mice with a purified chimeric NS1/HA2 influenza virus protein

Influenza A/PR/8/34-derived chimeric (D) protein (SK&F 106160) composed of the first 81 amino acids (aa) of NS1 fused to the conserved 157 C-terminal aa of HA2 (NS1 1-81-HA2 65-222) was previously shown to induce H-2d-restricted protective cytotoxic T-lymphocyte (CTL) immunity in inbred mice. However, D protein, like other small peptides, exhibited haplotype dependence and was not immunogenic in H-2b and H-2K mice. A potential use of this antigen in humans and the role of T cells in any protection were evaluated in outbred Swiss and inbred CBF6F1 (H-2d/b) mice. Mice immunized with D protein and challenged by small-particle aerosol with a lethal dose of influenza virus were significantly protected against mortality from influenza A/H1N1 and A/H2N2 (p < 0.05-< 0.0000001), but not from A/H3N2 and influenza B viruses when compared with control mice. D protein did not induce serum virus-neutralizing antibody but caused virus to be cleared faster in immunized mice. Protection was long-lasting. In vivo depletion of either Lyt2 (CD8+) or L3T4 (CD4+) T cells with monoclonal antibodies led to abrogation of in vitro-generated CTL activity in CF6F1 mice and significant reduction in the protective efficacy of D protein against virus challenge in both Swiss and CF6F1 mice. These results suggest that protection was mediated by CD8+ and/or CD4+ cells and not antibody. Thus D protein, via a conserved sequence on the HA2 polypeptide, has the potential to induce partially cross-reactive CTL that may protect against influenza virus disease in humans.

Primary pulmonary cytotoxic T lymphocytes induced by immunization with a vaccinia virus recombinant expressing influenza A virus nucleoprotein peptide do not protect mice against challenge

The nucleoprotein (NP) of influenza A virus is the dominant antigen recognized by influenza virus-specific cytotoxic T lymphocytes (CTLs), and adoptive transfer of NP-specific CTLs protects mice from influenza A virus infection. BALB/c mouse cells (H-2d) recognize a single Kd-restricted CTL epitope of NP consisting of amino acids 147 to 155. In the present study, mice were immunized with various vaccinia virus recombinant viruses to examine the effect of the induction of primary pulmonary CTLs on resistance to challenge with influenza A/Puerto Rico/8/34 virus. The minigene ESNP(147-155)-VAC construct, composed of a signal sequence from the adenovirus E3/19K glycoprotein (designated ES) and expressing the 9-amino-acid NP natural determinant (amino acids 147 to 155) preceded by an alanine residue, a similar minigene NP(Met 147-155)-VAC lacking ES, and a full-length NP-VAC recombinant of influenza virus were analyzed. The two minigene NP-VAC recombinants induced a greater primary pulmonary CTL response than the full-length NP-VAC recombinant. However, NP-specific CTLs induced by immunization with ESNP(147-155)-VAC did not decrease peak virus titer or accelerate clearance of virus in the lungs of mice challenged intranasally with A/PR/8/34. Furthermore, NP-specific CTLs induced by immunization did not protect mice challenged intranasally with a lethal dose of A/PR/8/34. Sequence analysis of the NP CTL epitope of A/PR/8/34 challenge virus obtained from lungs after 8 days of replication in ESNP(147-155)-VAC-immunized mice showed identity with that of the input virus, demonstrating that an escape mutant had not emerged during replication in vivo. Thus, in contrast to adoptively transferred CTLs, pulmonary NP-specific CTLs induced by recombinant vaccinia virus immunization do not have protective in vivo antiviral activity against influenza virus infection.

Effects of experimental infection with border disease virus on lymphocyte subpopulations in the peripheral blood of lambs

Experimental infection with Border disease virus was characterised by significant changes in the total numbers of leucocytes and neutrophils, and in the proportions and numbers of the different lymphocyte subpopulations. Three days after experimental infection there was significant leucopenia due to lymphocytopenia and neutropenia (P < 0.001). The lymphocytopenia and neutropenia lasted for up to seven days after inoculation. The lymphocytopenia was due to a reduction in the number of both T cells and B cells. During the early period of infection, the reduction in T cells was mainly due to a reduction in the number of OvCD4+ and T-19+ lymphocytes as the number of circulating OvCD8+ cells was not significantly affected. The cells expressing the OvCD4 and OvWC1 epitopes returned to pre-inoculation values 10 and 14 days after inoculation, respectively. In contrast, during the same period, the number of T cells expressing the OvCD8 molecule became significantly higher than the corresponding pre-inoculation values. There were no significant changes in all the T cell subsets in the control lambs.

Cell-to-cell contact not soluble factors mediate suppression of lymphocyte proliferation by bovine parainfluenza virus type 3

We have previously characterized the ability of parainfluenza virus type 3-infected (PIV-3) and noninfected bovine alveolar macrophages (BAM) to support lymphocyte proliferation. While uninfected macrophages support proliferation of lymphocytes stimulated with concanavalin A (Con A), ovalbumin, and interleukin 2 (IL-2), lymphocyte [3H]thymidine incorporation was suppressed in the presence of PIV-3-infected BAM. Since viral infection of macrophages has been shown to alter arachidonic acid metabolism and cytokine secretion, we have determined if arachidonate metabolism or the lack of IL-1 and IL-2 mediated the suppression of lymphocyte proliferation by PIV-3. Inhibition of arachidonic acid metabolism failed to reverse the suppressive effect of viral infection as did supplementation of cultures with bovine recombinant IL-1 beta, IL-2, or lymphocyte-conditioned medium. Further, lymphocytes proliferated normally when physically separated from virus infected BAM by a semipermeable membrane. Stimulation of lymphocytes in contact with infected BAM resulted in marked suppression of lymphocyte [3H]thymidine incorporation. Interactions between stimulated lymphocytes and PIV-3-infected BAM resulted in PIV-3 infection of lymphocytes. Virus infection of lymphocytes was confirmed ultrastructurally by the presence of characteristic parainfluenza virus inclusions and virus budding from lymphocyte plasma membranes. It was concluded that suppression of lymphocyte proliferation by PIV-3 is mediated in part by infection of stimulated lymphocytes during cell-to-cell contact with BAM.

Induction of CD8+ cytotoxic T cells by immunization with killed influenza virus and effect of cholera toxin B subunit

The MHC class I cytotoxic T-lymphocyte (CTL) response in mice given formalin-inactivated influenza whole-virus vaccine (WVV) with or without cholera toxin B subunit (CTB) was studied. Intraperitoneal injection of Balb/c (H-2d) mice with high doses of A/Taiwan/1/86 (H1N1) WVV stimulated influenza A virus-specific CTL response in a dose-dependent manner. A dose of 4.4 or 44 micrograms induced CTL response equal to or greater than live influenza virus infection. Coadministration of vaccine with 5 or 25 micrograms of CTB resulted in a higher level of CTL than with vaccine alone. CTL lysed A/Taiwan and A/Shanghai (H3N2) virus-infected class I-expressing P815 (H-2d) but not virus-infected EL-4 (H-2b) target cells nor B/Yamagata virus-infected target cells. Virus-infected MHC class II- and class I-expressing A20 (H-2d) targets were also lysed. Depletion of Lyt-2+ (CD8+) T cells with monoclonal antibody completely abrogated lysis of P815 target cells and resulted only in a slight reduction of lysis of A20 target cells. Depletion of L3T4+ (CD4+) T cells or NK cells had minimal effect on lysis of either P815 or A20 target cells. Using limiting dilution analysis, the precursor CTL (pCTL) frequency paralleled CTL activity. Significant CTL activity was detected 7 months after immunization. These results demonstrate that adequate doses of influenza WVV with or without CTB can induce long-lasting influenza A cross-reactive MHC class I-restricted CD8+ CTL response in mice. Thus, coadministration of influenza WVV with CTB may lead to an effective vaccine that stimulates both CTL and antibody responses.

Analysis of T lymphocyte subsets proliferating in response to infective and UV-inactivated African swine fever viruses

The proliferative response to infective and UV-inactivated African swine fever virus was analyzed in cells from pigs surviving an experimental infection with attenuated virus. All the pigs showed strong dose-dependent proliferative responses to both infective and UV-inactivated virus. This response was also observed when nitrocellulose-bound solubilized virus proteins were used in the assay. Heterologous isolates also induced proliferation, however it was significantly lower than that induced by the isolate used to infect the animals. The response to infective virus was blocked equally by anti-CD4 and anti-CD8 monoclonal antibodies (mAb); the response to UV-inactivated virus was almost abolished by anti-CD4 and 60% inhibited by anti-CD8 mAb. FACS analysis of 28-day T cell lines derived from peripheral blood mononuclear cells demonstrated the progressive increase of the CD8+ subset when the cells were stimulated with infective virus, whereas the stimulation with UV-inactivated virus induced the increase of both CD4+ and CD8+ subsets. In this case, the sum of CD4+ and CD8+ percentages was higher than the total percentage of T cells, suggesting the presence of cells positive for both CD4+ and CD8+.

Virus entry and antigen biosynthesis in the processing and presentation of class-II MHC-restricted T-cell determinants of influenza virus

Receptor-mediated uptake of influenza virus is responsible for efficient introduction of virus particles to APC. This leads to the effective presentation to T-cells of very small concentrations of proteins entering on the intact virus. Endocytosed virus transits rapidly to the endosome compartment. Entry into this environment appears to greatly affect the fate of T-cell determinants. While promoting the presentation of determinants which require extensive antigen processing, the intracellular environment appears also to lead to destruction of labile determinants, such as those of NA. The same NA determinants are efficiently presented by actively infected cells, indicating that newly biosynthesized viral proteins need not be subjected to the same handling as internalized viral particles. In a similar way, site 3 of HA, which, in a single pulse of noninfectious virus or isolated HA protein is expressed with a relatively short half-life, has greatly improved levels of duration and expression on actively infected APC. Since certain T(H) determinants are unavailable or poorly expressed when introduced on nonreplicative influenza virus, vaccination with inactivated virus might have limitations in stimulating T(H) as well as class-I responses. Finally, individual T-cell determinants of the same protein can exhibit distinct patterns of expression and persistence on APC surfaces. These different half-lives of T(H) determinants may be influential in determining immuno-dominance of T-cell sites. Determinants that are longer-lived on APC may have a greater probability of interacting with appropriate T(H) precursors, which could lead to an enhanced T-cell response to that region of the viral protein.

Lymphocyte subpopulations in peripheral blood of lambs experimentally infected with bovine respiratory syncytial virus

The lymphocyte subpopulations of peripheral blood of normal lambs and lambs experimentally infected with bovine respiratory syncytial virus (RSV) were analysed by flow cytometry, using a panel of monoclonal antibodies against specific lymphocyte epitopes. Experimental infection with bovine RSV was characterized by a significant rise in SBU-T8+ (CD8+ or cytotoxic) T cells and a significant reduction in SBU-T4+ (CD4+ or helper) T cells and B (LCA p220+) lymphocytes (P less than 0.05). The helper/suppressor (CD4/CD8) ratio was reduced from 3.91 on the day of experimental infection to 1.13 on 10 days after experimental infection (P less than 0.001). The total number of SBU-T4+ (CD4+) and B cells returned to pre-inoculation values 14 days after experimental infection but the helper/suppressor ratio remained depressed up to 21 days post-inoculation.

Vaccination with inactivated influenza A virus during pregnancy protects neonatal mice against lethal challenge by influenza A viruses representing three subtypes

A single intraperitoneal injection of pregnant mice with a monovalent Formalin-inactivated influenza A virus vaccine protected their offspring against a lethal challenge dose of the same influenza A virus H3N2, H2N2, and H1N1 subtypes, as well as against challenge with the other two subtypes. Degree of protection was vaccine dose related. Cross-fostering of neonates indicated that protection was conferred by breast milk antibodies. Serum virus-specific neutralizing antibodies in the mothers and neonates correlated with resistance to vaccine virus, but were detected against other subtypes only in a complement enhancement test or when high doses of vaccine were given.

Class I H-2d-restricted cytotoxic T lymphocytes recognize the neuraminidase glycoprotein of influenza virus subtype N1

Class I major histocompatibility complex-restricted cytotoxic T lymphocytes (CTL) that recognize the neuraminidase (NA) glycoprotein of subtype N1 influenza A viruses have been demonstrated in BALB/c mice. Responses to NA were obtained only in protocols that use two in vivo inoculations of virus, including a recombinant vaccinia virus containing the NA of subtype N1 influenza virus (NA-VAC) to prime or boost. Restimulation in vitro was also required for CTL recognition of NA and strongly depended on the specific N1 virus used. Influenza viruses A/Puerto Rico/8/34 (H1N1), A/CAM/46 (H1N1), J1 (H3N1), and JAP/BEL (H2N1), but not A/Bellamy (H1N1) or MEM/BEL (H3N1) virus, were able to stimulate NA-specific memory T cells in vitro. Single or double in vivo inoculation of any of the N1 viruses or a single injection of NA-VAC failed to elicit restimulatable NA-specific CTL. Lysis of NA-VAC-infected cells at low effector/target ratios was comparable to that observed toward other influenza virus proteins known to be major targets of CTL in BALB/c mice, indicating that antigenic determinants of the subtype N1 NA molecule can be efficiently presented in the context of major histocompatibility complex class I.

Local administration of cytostatic drugs enhances delayed-type hypersensitivity to Sendai virus in mice

Cytostatic drugs known to exert immunomodulatory activity were studied in a local treatment protocol as to their effect on development of cell-mediated immunity to Sendai virus in mice. Strong enhancement of delayed-type hypersensitivity (DTH) was observed after treatment with the active cyclophosphamide (CY) derivative Z 7557 or the plant alkaloid VP-16 at the site of sensitization. Optimal enhancement of DTH was obtained after priming with subimmunogenic doses of Sendai virus and treatment with low, virtually nontoxic drug doses. Immunoenhancement is ascribed to elimination of CY-sensitive suppressor cells from the draining lymph nodes. The relevance of our findings with respect to protective immunity is discussed.

Mechanism of recovery from acute virus infection. VIII. Treatment of lymphocytic choriomeningitis virus-infected mice with anti-interferon-gamma monoclonal antibody blocks generation of virus-specific cytotoxic T lymphocytes and virus elimination

In acutely infected mice the lymphocytic choriomeningitis (LCM) virus multiplies to high titers in essentially all tissues. Around day 6, virus clearance sets in, which has previously been shown to be mediated by CD8+ cytotoxic T lymphocytes (CTL), probably by releasing (or inducing other cells to release) anti-viral cytokines. To ascertain whether interferon-gamma plays a role, infected mice were injected once i.v. with monoclonal antibody known to neutralize this lymphokine, and the effect this had on both termination of the infection and development of LCM virus-specific CTL was determined. Administration 1 day after infection blocked virus elimination from spleen and liver and decreased the generation of CTL; also, limiting dilution analysis revealed absence of activation of CTL precursors. In contrast, when the antibody was given 3 days after or 1 day before the virus, neither clearance nor generation of CTL was measurably affected. Furthermore, the antiviral effect of immune spleen cells after their transfer into infected recipients was not altered by treatment of the latter with monoclonal antibody. We conclude that in the generation of LCM virus-specific CTL an early event is dependent on constitutively produced interferon-gamma; when its activity is blocked, CTL do not mature, resulting in the mouse's inability to terminate the infection.

Intranasal immunization with proteoliposomes protects against influenza

Worldwide, influenza virus remains a serious disease which has successfully eluded numerous attempts to design a consistently effective vaccine. In part, these attempts have been thwarted because of a lack of basic understanding of the mechanisms which mediate protection and recovery from influenza infection. A better understanding of the roles of secretory antibody, serum antibody and cell mediated immunity vis-à-vis protection and recovery from influenza infection has allowed us more rationally to approach the design and administration of a vaccine for influenza. We have constructed a vaccine composed of glycoproteins from the envelopes of either influenza of Sendai virus embedded in a lipid bilayer (immunosomes) mimicking the presentation of the virus to the cells during natural infection. Intranasal immunization with these immunosomes induces an adequate systemic Ir compared with intramuscular immunization and a superior local IgA response. These animals were specifically protected from virus challenge.

Class II major histocompatibility complex-restricted T cells specific for a virion structural protein that do not recognize exogenous influenza virus. Evidence that presentation of labile T cell determinants is favored by endogenous antigen synthesis

The contribution of viral infectivity to the expression of MHC class II-restricted T cell determinants was studied. A murine I-Ed-restricted T cell hybridoma recognizing the neuraminidase (NA) glycoprotein of influenza PR8 virus was stimulated strongly by infectious virus but failed to recognize antigen introduced on noninfectious virions. Recognition correlated with the de novo synthesis of viral NA within infected APC. The effectiveness of infectious virus did not depend strictly upon the amount of NA present in cultures, since high NA concentrations could be achieved by addition of nonreplicative virus without being stimulatory for NA-specific T cells. Recognition of a determinant generated only when synthesized in murine host cells was ruled out, since, in high concentration, NA isolated from purified egg-grown virions, even if reduced and alkylated, was recognized by the T hybridoma clone. Isolated NA was recognized when added to pre-fixed APC, suggesting that this form of antigen was able to bypass the usual processing pathway of exogenous proteins. Data suggest that endogenously synthesized antigen may contribute most significantly to presentation of labile T cell determinants. In addition to NA, recognition of an I-Ed-restricted determinant of the influenza hemagglutinin (HA) molecule, shown previously to have a relatively short half-life on APC surfaces, was enhanced greatly by infectious virus. In contrast, T cell recognition of a more stably expressed I-Ed-restricted site of the same HA polypeptide was only marginally improved on infected APC.

Herpes simplex virus (HSV)-specific proliferative and cytotoxic T-cell responses in humans immunized with an HSV type 2 glycoprotein subunit vaccine

Studies were undertaken to determine whether immunization of humans with a herpes simplex virus type 2 (HSV-2) glycoprotein-subunit vaccine would result in the priming of both HSV-specific proliferating cells and cytotoxic T cells. Peripheral blood lymphocytes (PBL) from all eight vaccines studied responded by proliferating after stimulation with HSV-2, HSV-1, and glycoprotein gB-1. The PBL of five of these eight vaccines proliferated following stimulation with gD-2, whereas stimulation with gD-1 resulted in relatively low or no proliferative responses. T-cell clones were generated from HSV-2-stimulated PBL of three vaccinees who demonstrated strong proliferative responses to HSV-1 and HSV-2. Of 12 clones studied in lymphoproliferative assays, 9 were found to be cross-reactive for HSV-1 and HSV-2. Of the approximately 90 T-cell clones isolated, 14 demonstrated HSV-specific cytotoxic activity. Radioimmunoprecipitation-polyacrylamide gel electrophoresis analyses confirmed that the vaccinees had antibodies only to HSV glycoproteins, not to proteins which are absent in the subunit vaccine, indicating that these vaccinees had not become infected with HSV. Immunization of humans with an HSV-2 glycoprotein-subunit vaccine thus results in the priming of T cells that proliferate in response to stimulation with HSV and its glycoproteins and T cells that have cytotoxic activity against HSV-infected cells. Such HSV-specific memory T cells were detected as late as 2 years following the last boost with the subunit vaccine.

Genetic control of T cell responsiveness to the Friend murine leukemia virus envelope antigen. Identification of class II loci of the H-2 as immune response genes

T cells primed specifically for the envelope glycoprotein of Friend murine leukemia helper virus (F-MuLV) were prepared by immunizing mice with a recombinant vaccinia virus that expressed the entire env gene of F-MuLV. Significant proliferative responses of F-MuLV envelope-specific, H-2a/b T cells were observed when the T cells were stimulated with antigen-pulsed peritoneal exudate cells (PEC) having the b allele at the K, A beta, A alpha, and E beta loci of the H-2. On the other hand, PEC having only the kappa allele at these loci did not induce the envelope-specific T cell proliferation, even when the PEC had the b allele at the E alpha, S, or D loci. F-MuLV envelope-specific proliferation of H-2a/b T cells under the stimulation of antigen-pulsed, H-2a/b PEC was specifically blocked with anti-I-Ab and anti-I-Ek mAbs but not with anti-Kb, anti-Kk, or anti-I-Ak mAbs. Moreover, (B10.MBR x A/WySn)F1 mice that have the b allele only at the K locus but not in I-A subregion were nonresponders to the envelope glycoprotein, and the bm12 mutation at the A beta locus completely abolished the T cell responsiveness to this antigen. These results indicate that proliferative T cells recognize a limited number of epitopes on F-MuLV envelope protein in the context of I-Ab, hybrid I-Ak/b, and/or hybrid I-Ek/b class II MHC molecules but fail to recognize the same envelope protein in the context of I-Ak or I-Ek molecules. This influence of the H-2I region on T cell recognition of the envelope glycoprotein appeared to control in vivo induction of protective immunity against Friend virus complex after immunization with the vaccinia-F-MuLV env vaccine. Thus, these results provide, for the first time, direct evidence for Ir gene-controlled responder/nonresponder phenotypes influencing the immune response to a pathogenic virus of mice.

Establishment of cytotoxic T-cell clones specific for cells infected with mouse hepatitis virus

Mouse hepatitis virus (MHV)-specific T-lymphocyte clones were established from MHV-infected BALB/c mice. They expressed Thy1 and Lyt2 antigens but lacked L3T4 and NK1 antigens. The clones killed MHV-infected but not uninfected or influenza virus-infected J774.1 cells. The specificity was further defined by a cold-target competition test.

Reduction of influenza virus pathogenesis by exposure to 0.5 ppm ozone

Continuous exposure to 0.5 ppm ozone during the course of murine influenza A/PR8/34 virus infection reduced the severity of the disease as quantitated by histologic (morphometric), biochemical (serum albumin in lavage fluid), and gravimetric (lung wt/dry weight ratios) parameters of lung injury. The ozone-mediated abatement of the lung injury was independent of peak pulmonary virus titers. However, determination of the sites of virus multiplication indicated that exposure to ozone resulted in a less widespread infection of the lung parenchyma. Furthermore, ozone exposure reduced the antiviral immune response as shown by reduced numbers of phenotypically quantitated T- and B-lymphocytes recovered from lung tissues and reduction of serum antibody titers. Since the pathogenesis of influenza virus infection depends on both the site of viral replication and the antiviral immune response, these studies suggest that redistribution of virus growth in murine lungs and immunosuppressive mechanisms are factors in the ozone-reduced disease severity.

Long-term depletion of CD8+ T cells in vivo in the rat: no observed role for CD8+ (cytotoxic/suppressor) cells in the immunoregulation of experimental allergic encephalomyelitis

A method is described for the long-term depletion of CD8+ T cells in the rat. Employing Lewis rats depleted of this cell type it is shown that such animals acquire, and subsequently recover from both passively and actively induced experimental allergic encephalomyelitis (EAE) in a comparable fashion to normal animals. Furthermore, after spontaneous recovery from the initial bout of disease, CD8+ T cell-depleted rats do not show any signs of relapse and, like normal rats following recovery from active EAE, are still resistant to further attempts at disease induction. Overall, these data do not support a role for the classic cytotoxic/suppressor (CD8+) T cell in the immunoregulation of EAE in the Lewis rat.

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.

Prospects for molecular vaccines in veterinary parasitology

Despite the profound developments in recombinant DNA technology there is only one marketed recombinant vaccine (for human viral hepatitis B). The development of others proceeds with great difficulty. Molecular vaccines against veterinary parasites are at the utmost pole of complexity in the spectrum of potential vaccines since these parasites are complex eukaryotic organisms, often dwelling at mucosal surfaces where anamnestic responses are problematic, where the immunogenicity of the parasite components is poorly understood and where the effector mechanisms of immunity are unresolved. Cloning a "protective" gene is only the first step, and perhaps the easiest, in a long process which will be necessary to develop vaccines against parasites. Additional steps will involve comprehensive analyses of the immunological responses to ensure that vaccine antigens contain the correct epitopes to induce appropriate immune effector mechanisms for parasite elimination and immunological memory and that these responses are not genetically restricted. The great expectations for recombinant vaccinia-based vaccines must be modified substantially in the light of recent evidence indicating immunological and other constraints on this approach. The use of anti-idiotype vaccines is an underexplored opportunity for practical parasite vaccines since they have several potentially important advantages. The need to include T cell antigenic peptides in peptide vaccines to extend the range of genetic responsiveness and to induce anamnestic responses is now clear. New algorithms for the prediction of such sites exist and these can be tested experimentally with synthetic peptides. There are no major technical obstacles to the development of vaccines for parasites which cannot be overcome. However substantial long term basic research is needed over a range of disciplines to achieve this worthwhile objective.

The cytotoxic response to murine cytomegalovirus: requirements for the generation of MCMV-specific target cells

The preparation of target cells susceptible to lysis by murine cytomegalovirus (MCMV)-immune T cells in vitro was investigated and found to be dependent upon target cell type, culture conditions, virus adsorption protocol and virus preparation. Optimally sensitive MCMV-infected targets were obtained by preculture of mouse embryo fibroblasts (MEF) in 3% vol/vol concanavalin-A-stimulated spleen cell supernatant (CSS)-supplemented medium, adsorption of salivary gland stock MCMV under 800 g centrifugation and at least 4 h further incubation at 37 degrees before addition of T cells. In contrast, salivary gland stock MCMV did not cause thioglycollate-induced peritoneal exudate cells to be susceptible to MCMV-specific T cell-mediated lysis, whereas tissue culture-passaged stock MCMV was successful. The preparation of MCMV-infected target cells is discussed in terms of the need for H-2 and viral antigen expression for T cell recognition.

The regulation of herpes simplex virus-specific CTL induction by suppressor cells

The incubation of herpes simplex virus (HSV) immune murine splenocytes with HSV antigens induced suppressor cells which inhibited HSV-specific cytotoxic T lymphocyte (CTL) induction. The cell mediating the suppression was identified as a Thy 1+ Lyt 2+ I-J+ cell. The induction of this suppressor cell required the participation of at least three leukocyte populations. That is, depleting the cultures of either Lyt 1+ or Lyt 2+ splenocytes resulted in a failure to induce suppressor cell activity. Likewise the removal of macrophage-like antigen-presenting cells (APC), in particular I-A- I-J+ APC, abolished suppressor-cell induction. Though the Lyt 2+ I-J+ cells had to be provided by HSV-immune mice, both the APC and the Lyt 1+ cells could be provided by HSV-naive mice. Though the induction of the suppressor cell was virus specific, its action was nonspecific as evidenced by the suppression of influenza-specific CTL induction. The implication of our results for the understanding and manipulation of herpesvirus disease is briefly discussed.

Delayed type hypersensitivity responses to the Qa-Tla region of the mouse major histocompatibility complex

We have elicited a small but significant delayed-type hypersensitivity response against the Qa-Tla region of H-2 following immunisation of C57BL/6 mice with cells from the congenic strain C57BL/6.Tlaa. Optimal responses were detected 14 days after immunisation with 10-40 X 10(6) cells. The significance of delayed type hypersensitivity to Qa-Tla is discussed in relation to the genetic loci which map to this region.

T-cell effector function and unresponsiveness in the murine lymphocytic choriomeningitis virus infection. II. Delayed-type hypersensitivity unresponsiveness reflects a defective differentiation from TD precursor to effector cell

An increase in the virus dose from 10(2) LD50 (low dose) to 10(4) LD50 (high dose) of lymphocytic choriomeningitis virus (LCMV) results in markedly delayed virus clearance, in spite of a potent cytotoxic T-cell (TC) response. However, virus-specific delayed-type hypersensitivity (DTH) reactivity is markedly depressed in high-dose mice, suggesting an association between DTH and virus clearance. When virus-primed memory cells are transferred, DTH reactivity as well as virus-clearing capacity is restored in high-dose mice, indicating that the virus is not present in a changed or concealed form. The role of T-cells mediating DTH (TD cells) in virus clearance was also studied by adoptive transfer to naive recipients. Here the high-dose primed cells did mediate virus clearance, although no DTH reaction was detectable 24-72 h after transfer. However, when footpad swelling was measured 96 h or more after transfer a DTH response emerged, indicating that TD priming had taken place in high-dose animals. Pre-irradiation of high-dose primed cells markedly inhibited the antiviral activity as well as DTH, suggesting that upon transfer to naive recipients TD precursors from high-dose mice would proliferate into effector cells capable of mediating both functions. Treatment with anti-Lyt2+C' abrogated the capacity to induce virus-specific DTH, thus confirming that the cells involved are not helper T (TH) cells. We conclude that the DTH unresponsiveness in high-dose mice reflects a defective differentiation of TD precursor into effector cells which is reversible upon transfer to a less antigen loaded environment. Furthermore, it is suggested that TD function is crucial to the process of virus clearance.

The role of IL-2 and T4+ cells in the generation of human influenza virus-specific CTL activity

Stimulation of human peripheral blood lymphocytes (PBL) with influenza A virus leads to the generation of virus-specific cytotoxic T lymphocyte (CTL) activity as well as natural killer (NK)-like activity. In this study, we show that exogenous IL-2 augments the in vitro generation of virus-specific CTL activity, only when added some days after the initiation of the culture. Apparently, the endogenously produced IL-2 can be a limiting factor in the in vitro generation of CTL activity. The increase of influenza virus-specific CTL activity after addition of exogenous IL-2 does not affect the restriction pattern of the CTL response. So, the preferential use of certain HLA antigens as restriction elements is not due to a limiting amount of endogenously produced IL-2. Depletion of T4+ cells completely abrogates the generation of virus-specific CTL activity. Addition of exogenous IL-2 to T4+-cell-depleted cultures fully restores the generation of HLA-restricted virus-specific CTL activity. We conclude that in the in vitro generation of virus-specific CTL activity in bulk cultures of human PBL the sole function of T4+ cells in human virus-specific CTL generation is the production of IL-2, no cognitive cell interaction of T8+ CTL precursors with T4+ cells is required, and in bulk cultures T8+ cells themselves are not able to produce sufficient amounts of IL-2 to ascertain the maturation of virus-specific CTL precursors into cytolytic T cells. Finally, we show that exogenous IL-2 also has a stimulatory effect on the NK-like or lymphokine-activated killer activity, which is always concomitantly induced in virus-specific CTL generation cultures, but has no influence on the levels of IFN produced in such cultures.

Differences in antigen presentation to MHC class I-and class II-restricted influenza virus-specific cytolytic T lymphocyte clones

We have examined requirements for antigen presentation to a panel of MHC class I-and class II-restricted, influenza virus-specific CTL clones by controlling the form of virus presented on the target cell surface. Both H-2K/D- and I region-restricted CTL recognize target cells exposed to infectious virus, but only the I region-restricted clones efficiently lysed histocompatible target cells pulsed with inactivated virus preparations. The isolated influenza hemagglutinin (HA) polypeptide also could sensitize target cells for recognition by class II-restricted, HA-specific CTL, but not by class I-restricted, HA-specific CTL. Inhibition of nascent viral protein synthesis abrogated the ability of target cells to present viral antigen relevant for class I-restricted CTL recognition. Significantly, presentation for class II-restricted recognition was unaffected in target cells exposed to preparations of either inactivated or infectious virus. This differential sensitivity suggested that these H-2I region-restricted CTL recognized viral polypeptides derived from the exogenously introduced virions, rather than viral polypeptides newly synthesized in the infected cell. In support of this contention, treatment of the target cells with the lysosomotropic agent chloroquine abolished recognition of infected target cells by class II-restricted CTL without diminishing class I-restricted recognition of infected target cells. Furthermore, when the influenza HA gene was introduced into target cells without exogenous HA polypeptide, the target cells that expressed the newly synthesized protein product of the HA gene were recognized only by H-2K/D-restricted CTL. These observations suggest that important differences may exist in requirements for antigen presentation between H-2K/D and H-2I region-restricted CTL. These differences may reflect the nature of the antigenic epitopes recognized by these two CTL subsets.

Enhancement of respiratory syncytial virus pulmonary pathology in cotton rats by prior intramuscular inoculation of formalin-inactiva ted virus

Cotton rats previously inoculated with Formalin-inactivated respiratory syncytial virus (RSV) were challenged intranasally with live RSV to induce an enhancement of RSV disease similar to that observed after the administration of Formalin-inactivated RSV vaccine to human infants 20 years ago. Within 24 h after infection with RSV, cotton rats developed pulmonary lesions that reached a maximum by day 4. Histologically, the lesions resembled an experimental pulmonary Arthus reaction. An action of Formalin on RSV appears to be responsible for this effect, because live virus or virus heated in the absence of Formalin did not induce enhanced immunopathology. Selected epitopes on the fusion (F) or attachment (G) or both RSV surface glycoproteins that are involved in inducing neutralizing antibodies were modified to reduce or ablate their antigenicity. However, other epitopes on the F or G or both glycoproteins were not ablated by Formalin, because cotton rats inoculated parenterally with a Formalin-inactivated virus developed a high level of F and G antibodies measurable by an enzyme-linked immunosorbent assay. At this time, the effect of Formalin on RSV cannot be localized to either the F or G glycoprotein of RSV.