The recognition of influenza A virus- infected cells by cytotoxic T lymphocytes

Identification of Kk-restricted T-cell epitope within influenza virus nucleoprotein

In order to determine the epitope structure in peptide NP50-63, which has been reported to be the only Kk-restricted T-cell antigen within the influenza virus (A/PR/8/34) nucleoprotein, a series of 13 peptides truncated from C- and N-termini of NP50-63 were synthesized and their sensitizing activities against Kk-restricted nucleoprotein-specific cytotoxic T lymphocytes (CTLs) were examined. One of the 13 peptides, NP50-57, sensitized L929 cells at the nM level, which was 100-1000 times lower in concentration than that at which the other peptides sensitized these cells. The presence of NP50-57 in A/PR/8/34-infected L929 cells was also investigated. Acid extracts of virus-infected cells were separated on a reverse-phase HPLC column and then anion-exchange column. By both separations, only one peak of sensitizing activity against nucleoprotein-specific CTLs was observed. The position of the peak coincided with that of the elution of NP50-57. These results strongly suggest that NP50-57 is the natural epitope in the antigenic structure, NP50-63.

Primary cytotoxic response of bovine peripheral blood leukocytes to parainfluenza type 3 virus infection

Peripheral blood mononuclear cells were isolated from calves following Parainfluenza Type-3 (PI-3) virus infection and incubated with autologous and non-autologous PI-3 virus-infected muscle cells in a 4 h chromium release assay. Peaks of cytotoxicity, which ranged from 12% to 53% were observed between Days 6 and 9 post infection, with an effector to target cell ratio of 100:1. Killing of PI-3 virus-infected or uninfected mismatched muscle cells was never more than 5%.

Protection of mice against an influenza virus infection by oral vaccination with viral nucleoprotein incorporated into immunostimulating complexes

Influenza A virus nucleoprotein (NP) was integrated into immunostimulating complexes (ISCOMs) after attachment of bacterial lipopolysaccharide to the antigen. Oral immunization with these NP-ISCOMs protected mice fully against an otherwise lethal challenge infection with an unrelated influenza virus subtype without the appearance of severe clinical signs or extensive pathological lesions in the lungs. Mice immunized with analogous bovine serum albumine-incorporated ISCOMs all died. After oral immunization, high titers of NP-specific antibodies, particularly IgA, could be detected in the bronchoalveolar fluid and in the blood serum. No cytotoxic lymphocytes could be demonstrated in the spleens or the lungs of vaccinated mice, and no anti-NP antibody-dependent cytolysis of infected host cells was mediated by complement or in the form of an antibody-dependent cell cytotoxicity. However, a vigorous delayed-type hypersensitivity reaction was produced after probing vaccinated animals with purified NP. No comparable protective immunity or antibody response was induced by a strictly intragastric administration of NP-ISCOMs. It appears, therefore, that the general and local immune response in the lungs was primarily stimulated through contact of NP-ISCOMs with the mucous membrane of the oro-pharyngeal cavity and that cytotoxic effects did not play a major role for the establishment of the protective immunity. Partial protection against a lethal challenge was observed in chickens immunized with NP-ISCOMs in the drinking water.

The proportion of herpes simplex virus-specific cytotoxic T lymphocytes (Tc) that recognize glycoprotein C varies between individual mice and is dependent on the form of immunization

In mice the immune response to HSV-1 includes a brisk Tc response that is intimately associated with the control of infection. This report evaluated the Tc response to gC, one of the envelope glycoproteins of HSV-1. This protein was recognized as a target antigen for Tc from HSV-1 immune mice only if they expressed the H-2Kb MHC allele. However, even within these "responder" strains of mice the proportion of gC specific Tc was highly variable. The failure of HSV-induced Tc to recognize gC in the context of other class 1 MHC haplotypes (H-2d and H-2k) was demonstrable at the clonal level and could not be attributed to peculiarities of the recombinant constructs. Surprisingly, despite the inability of H-2k-restricted, HSV-1-induced Tc to recognize gC, when a vaccinia gC virus construct was used to immunize H-2k strains of mice it showed a variable ability to induce memory Tc populations capable of lysing HSV-1-infected autologous cells. Of added importance was the correlation of this induced Tc response with optimum protection against subsequent challenge with HSV-1. This demonstrated that despite the presence of suitable epitopes, the context of the immunogen would also influence its ability to induce Tc. Consequently, the potential repertoire of available HSV-1-specific Tc specificities is larger than indicated by studying animals immunized with HSV.

Cytotoxic T cells isolated from the central nervous systems of mice infected with Theiler's virus

Intracerebral inoculation of resistant mice (C57BL/10SNJ) with Theiler's murine encephalomyelitis virus (TMEV) results in acute encephalitis followed by subsequent clearance of virus from the central nervous system (CNS). In contrast, infection of susceptible mice (SJL/J) results in virus persistence and chronic immune-mediated demyelination. Both resistance and susceptibility to TMEV-induced disease appear to be immune mediated, since immunosuppression results in enhanced encephalitis in resistant mice but diminished demyelination in susceptible mice. The purpose of these experiments was to determine whether anti-TMEV cytotoxic T lymphocytes (CTLs) are generated during acute and chronic TMEV infection. Nonspecific lectin-dependent cellular cytotoxicity was used initially to detect the cytolytic potential of lymphocytes infiltrating the CNS irrespective of antigen specificity. Using TMEV-infected targets, H-2-restricted TMEV-specific CTLs of the CD8+ phenotype were demonstrated in lymphocytes from the CNS of susceptible and resistant mice, arguing against the hypothesis that the ability to generate CD8+ CTLs mediates resistance. In chronically infected SJL/J mice, TMEV-specific CTL activity was detected in the CNS as late as 226 days postinfection. These experiments demonstrate that virus-specific CTLs are present in the CNS during both acute and chronic TMEV infection. Anti-TMEV CTLs in the CNS of chronically infected SJL/J mice may play a role in demyelination through their ability to lyse TMEV-infected glial cells.

Susceptibility to influenza A virus infection in mice immunosuppressed with cyclophosphamide

It is known that immunocompromised hosts show an enhanced susceptibility to microbial infections. Among these, viral infections represent a particular problem because of the lack of really efficient antiviral drugs. In the present report we have studied the effect of pharmacological immunosuppression with cyclophosphamide (CY) in virus infection in vivo, using Balb/c mice infected with influenza A virus (PR8). At the dose of 0.1 hemagglutinating units of viral inoculum, intranasal administration of PR8 virus caused the death of 50 to 60% of the animals within a period of 3-10 days. A single injection of CY (200 mg/kg) significantly increased mouse mortality to 90%, when PR8 virus challenge was performed 4 days after chemotherapy pretreatment. When the PR8 virus infection was performed at different times after CY-treatment, a similar appreciable effect was not observed. Severe alterations of some immunological parameters such as NK activity and analysis of lymphoid spleen cell subsets were related to the increased susceptibility to virus infection.

Immunogenicity of a non-class I MHC expressing murine tumor transfected with the influenza virus hemagglutinin or murine interleukin-2 genes

The transfection of murine SP1 tumor cells with the hemagglutinin (HA) gene of influenza virus results, after fluorescent-activated cell sorting (FACS), in the selection of high-HA-expressing cell lines called H4A and H4B. Both lines fail to grow in syngeneic animals at doses that result in 100% tumor take of non-transfected tumor cells. Both grow in immunosuppressed mice. SP1 and H4A or H4B cells express few class I major histocompatibility complex (MHC) antigens but do express class II IAk antigens. H4A or H4B cells engender a cytotoxic T lymphocyte (CTL) response but cannot protect against a challenge with SP1 cells. This CTL response is inhibited by anti-CD4 but not anti-CD8 antibodies. Using FACS, we were able to select a population (called H5AK5) with high class-I MHC antigen expression. Like H4A and H4B, H5AK5 cells fail to grow in syngeneic animals but do grow in immunosuppressed mice. However, unlike H4A or H4B, H5AK5 can induce protection against a challenge with 1 x 10(5) SP1 cells. These studies indicate that the immunogenicity of HA-transfected SP1 cells may correlate with the cell-surface expression of class II MHC antigens. However, HA-expressing SP1 cells seem able to induce a protective response against a parent SP1 cell challenge only if they also express class I MHC antigens. This view is supported by the observations that SP1 cells expressing murine interleukin-2 do not express class I MHC antigens, fail to grow in syngeneic animals, do grow in immunosuppressed mice but do not protect against a challenge with parental SP1 cells.

Lymphocytes cytotoxic to uveal and skin melanoma cells from peripheral blood of ocular melanoma patients

To study antitumor immunity in patients with choroidal melanoma, T cells were generated from the peripheral blood of choroidal melanoma patients by mixed lymphocyte/tumor cell culture (MLTC). Because autologous tumors are generally unavailable, an allogeneic choroidal melanoma cell line, OCM-1, was used as the specific stimulus. Lymphocyte cultures from 27 patients were characterized by cell-surface phenotypes, patterns of reactivity towards cells of the melanocytic origin and T-cell-receptor gene usage. Antimelanoma reactivity was found in cell-sorter-purified CD4+ and CD8+ T cell subsets. To analyze this reactivity, sorter-purified CD4+ and CD8+ cells from a MLTC were cloned by limiting dilution in the presence of exogenous interleukin-2 and interleukin-4 as well as irradiated OCM-1. Under these conditions, CD4+ T cells did not proliferate, perhaps because of the absence of antigen-presenting cells. However, CD8+ grew vigorously and 29 cytolytic CD8+ T cell clones were isolated. On the basis of their pattern of lysis of OCM-1, a skin melanoma cell line M-7 and its autologous lymphoblastoid cell line LCL-7, the clones were categorized into three groups. Group 1, representing 52% of the clones, lysed all three target cells, and are alloreactive. However, since OCM-1 and M-7 did not share class I antigens, these clones recognized cross-reactive epitope(s) of the histocompatibility locus antigen (HLA) molecule. Group 2, constituting 28% of the clones, lysed both the ocular and skin melanoma cell lines but not LCL-7, and were apparently melanoma-specific. Unlike classical HLA-restricted cytolytic T lymphocytes, these T cells might mediate the lysis of melanoma cells via other ligands or a more degenerate type of HLA restriction. For the latter, the HLA-A2 and -A28 alleles would have to act interchangeably as the restriction element for shared melanoma-associated antigen(s). Group 3, representing only 10% of the T cell clones, was cytotoxic only to OCM-1, but not to M-7 or LCL-7. These clones may recognize antigens unique to ocular melanoma cells. Our data suggest that choroidal melanoma patients can recognize melanoma-associated antigens common to both ocular and cutaneous melanoma cells, and presumbly their autologous tumor. Thus, choroidal melanoma, like its skin counterpart, may be responsive to immunotherapeutic regimens such as active specific or adoptive cellular immunotherapy.

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.

The 22,000-kilodalton protein of respiratory syncytial virus is a major target for Kd-restricted cytotoxic T lymphocytes from mice primed by infection

Recombinant vaccinia viruses containing the 22-kilodalton protein (matrixlike or 22K protein) or phosphoprotein gene from respiratory syncytial virus were constructed. These recombinant viruses expressed proteins which were immunoprecipitated by appropriate respiratory syncytial virus antibodies and comigrated with authentic proteins produced by respiratory syncytial virus infection. The new recombinant viruses (and others previously described containing the attachment glycoprotein, fusion, or nucleoprotein genes of respiratory syncytial virus) were used to infect target cells for cultured polyclonal cytotoxic T lymphocytes generated from the spleens of BALB/c or DBA/2 mice primed by intranasal infection with respiratory syncytial virus. Respiratory syncytial virus-specific cytotoxic T lymphocytes (CTL) showed strong Kd (but not Dd)-restricted recognition of the 22K protein. As previously reported, the fusion protein and nucleoprotein were both seen by CTL, but recognition of these proteins was comparatively weak. There was no detectable recognition of other respiratory syncytial virus proteins tested (including phosphoprotein). 22K protein-specific splenic memory CTL persisted for at least 11 months after infection of BALB/c mice. Priming BALB/c mice with recombinant vaccinia virus containing the 22K protein gene induced respiratory syncytial virus-specific memory CTL at lower levels than that previously reported following infection with a similar recombinant containing the fusion protein gene. These data identify the 22K protein as a major target antigen for respiratory syncytial virus-specific CTL from H-2d mice primed by respiratory syncytial virus infection.

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.

Immunogenic properties of ISCOM prepared with influenza virus nucleoprotein

After covalent attachment of bacterial lipopolysaccharide to the nucleoprotein of influenza A virus, this water-soluble antigen could be incorporated firmly into ISCOM. This potent "immunostimulating complex" induced the production of high antibody titers in mice and could partially protect the animals from a lethal challenge infection. After immunization with ISCOM preparations NP-specific cytotoxic T cell activity could not be demonstrated.

Cell-mediated immune responses to poliovirus. I. Conditions for induction, characterization of effector cells, and cross-reactivity between serotypes for delayed hypersensitivity and T cell proliferative responses

Human polioviruses are categorized into three distinct serotypes (types 1, 2, and 3) based upon their reactivity with specific antibodies. Although a great deal of information has been amassed about the induction and characterization of poliovirus antibody responses, little is known about cell-mediated immunity to poliovirus and its role in protection. Here, we show that intracutaneous injection of ultraviolet light-inactivated poliovirus into the tailbase of BALB/c mice induces delayed hypersensitivity (DTH) and T-cell proliferative (Tprlf) responses. Both DTH and Tprlf responses to poliovirus are mediated by Ly-1high2-, L3T4-bearing T cells. Moreover, known serologic cross-reactivity (i.e., antibody-mediated) of poliovirus serotypes is not predictive of cross-reactivity between the cell-mediated immune responses.

Regulation of lymphocyte proliferation after influenza virus infection of human mononuclear leukocytes

Previous studies demonstrated that in vitro infection with influenza A viruses altered several functions of human monocytes-macrophages but did not detectably alter functions of human lymphocytes. However, both types of cells were infected, as determined by production and surface expression of viral antigens. In the current studies, human mononuclear leukocytes were infected in vitro and assayed for both influenza virus-induced proliferation and mitogen (phytohemagglutinin [PHAl)-induced proliferation, as well as for ability to stimulate proliferative responses by normal autologous leukocytes. The leukocytes showed proliferation in response to the infectious virus, but concomitant depressed proliferative responses to PHA. Coculture experiments suggested suppression of PHA-induced responses by the virus-infected cells. However, upon coculture with fresh autologous leukocytes (without PHA stimulation), both virus-infected macrophages and virus-infected lymphocytes induced autologous lymphocyte proliferative responses. Altered proliferative responses to mitogen stimulation after exposure to the virus were not due to diminished interleukin-1 production or diminished expression of HLA-DR by monocytes-macrophages. The expression of influenza virus antigens and resulting induction of autologous proliferative responses, combined with depressed mitogen-induced proliferation, may be important in human antiviral defense.

Pathways of viral antigen processing and presentation to CTL: defined by the mode of virus entry?

Processing requirements for antigen presentation to cytotoxic T lymphocytes (CTL) vary among viruses and between major histocompatibility complex (MHC) class I- and class II-restricted responses to the same virus. In this article, Eric Long and Steven Jacobson argue that the mode of virus entry may define processing pathways and that the invariant chain associated with MHC class II molecules may account for the distinct processing requirements for MHC class I- and class II-restricted CTL.

Recognition of influenza virus-infected B-cell lines by human influenza virus-specific CTL

The cytotoxic activity on influenza virus-infected Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell lines (LCL-Flu) and influenza virus-infected phytohemagglutinin lymphoblasts (PHA-Flu) was compared with the use of influenza-A virus-specific cytotoxic T lymphocytes (CTL), generated in short-term bulk cultures. Cold-target inhibition experiments showed that the lysis of PHA-Flu was completely blocked by both cold LCL-Flu and cold PHA-Flu whereas the lysis of LCL-Flu was completely inhibited by cold LCL-Flu, but only partially by cold PHA-Flu, indicating that structures can be recognized on LCL-Flu which are absent from PHA-Flu. Monoclonal antibody (McAb) directed against a monomorphic determinant of major histocompatibility complex (MHC) class I molecules inhibited the lysis of PHA-Flu more strongly than the lysis of LCL-Flu. Since LCL have a high expression of MHC class II molecules compared to PHA lymphoblasts, we examined whether class II-restricted CTL activity was responsible for the (anti)class I McAb-resistant lysis of LCL-Flu. Neither anti-CD4 McAb nor anti-class II McAb inhibited the lysis of LCL-Flu which argues against a contribution of MHC class II-restricted CTL. Depletion of CD16+ cells, containing the majority of the nonspecific cytotoxic cells, did not affect the lysis of LCL-Flu, indicating that the remaining lysis on LCL-Flu was also not due to a nonspecific component. We suggest that cell-type-dependent variations exist in the nature of the immunogenic determinants to which CTL respond.

Mycobacteria-reactive Lyt-2+ T cell lines

The biological activities of mycobacteria-reactive Lyt-2+ T cells were characterized in vitro. T cells from mice immunized with killed Mycobacterium tuberculosis or viable M. bovis were restimulated in vitro and cloned under limiting dilution conditions. Several L3T4-Lyt-2+ T cell lines, some of them KJ16+, were established. These T cell lines were capable of lysing mycobacteria-primed macrophages in an antigen-specific way. The cytolytic activity of some T cell lines was found to be class I restricted, whereas others showed antigen-specific killing in the absence of apparent H-2 restriction. Several T cell lines produced interferon-gamma after appropriate stimulation. Furthermore, these T cell lines could induce tuberculostatic macrophage capacities by apparently two different mechanisms, namely by secretion of lymphokines (most probably interferon-gamma) and by direct cell contact. We conclude that CD8 T cells with antigen-specific cytolytic potential are generated during tuberculosis and that these T cells are involved in the immune response to tubercle bacilli.