Immune response in humans after vaccination with vaccinia virus: generation of a virus-specific cytotoxic activity by human peripheral lymphocytes

HIV antibodies for treatment of HIV infection

The bar is high to improve on current combination antiretroviral therapy (ART), now highly effective, safe, and simple. However, antibodies that bind the HIV envelope are able to uniquely target the virus as it seeks to enter new target cells, or as it is expressed from previously infected cells. Furthermore, the use of antibodies against HIV as a therapeutic may offer advantages. Antibodies can have long half-lives, and are being considered as partners for long-acting antiretrovirals for use in therapy or prevention of HIV infection. Early studies in animal models and in clinical trials suggest that such antibodies can have antiviral activity but, as with small-molecule antiretrovirals, the issues of viral escape and resistance will have to be addressed. Most promising, however, are the unique properties of anti-HIV antibodies: the potential ability to opsonize viral particles, to direct antibody-dependent cellular cytotoxicity (ADCC) against actively infected cells, and ultimately the ability to direct the clearance of HIV-infected cells by effector cells of the immune system. These distinctive activities suggest that HIV antibodies and their derivatives may play an important role in the next frontier of HIV therapeutics, the effort to develop treatments that could lead to an HIV cure.

Smallpox: the basics

Variola major is the causative agent of smallpox, a severe disease that was arguably one of the most serious human pathogens in recorded history. Humans are the only known reservoir of variola major; no known animal or insect reservoirs have been identified. Thus, after eradication of smallpox through a global immunization effort, this incredibly lethal scourge was eliminated from all corners of the globe. Despite the total eradication of naturally occurring smallpox, there are still stockpiles of smallpox virus maintained in the United States and the former Soviet Union. Unfortunately, it is impossible to know if all smallpox stocks have been accounted for or whether unknown or unreported stocks of smallpox may still exist. In the age of genetic engineering, these viruses could theoretically be modified to increase their virulence to the levels associated with smallpox itself.

Smallpox vaccine: problems and prospects

Smallpox justifiably is feared because of its morbidity and mortality. Wide-spread population-level susceptibility to smallpox exists, and the only effective tool against the virus is a live, attenuated vaccine that is highly reactogenic and controversial. A significant minority of the population has contraindications that prevent preexposure use of this vaccine. Newer, safer, and equally immunogenic vaccines must be developed and licensed. Several live, attenuated vaccines are in clinical trials. Although these vaccines may prove to be less reactogenic, they still may not be administered safely to a significant portion of the population because they contain live, attenuated viruses. Newer vaccines will be needed if routine preexposure vaccination is to be instituted universally. The idea of a subunit or peptide-based vaccine is appealing, because it obviates potential safety concerns. It may be possible to use a more-attenuated, live vaccine strain for a large segment of the population on a preexposure basis and accept the morbidity and mortality that would result from its use on a postexposure basis, if necessary. The need for widespread population-level protection against variola infection is apparent. The use of the new biology tools to predict or define who might experience serious reactions to the smallpox vaccine and why these reactions occur is an area ripe for additional research. The reason why an individual develops postvaccinal encephalitis remains unknown, and the development is unpredictable and untreatable. In the future, if the mechanism behind such adverse events is defined, it may be possible to screen persons who are likely to experience such events. Although the authors remain proponents for use of the vaccine in alignment with the CDC vaccination program and recommendations, the previous concerns indicate that new knowledge must be gained and shared. Further research on attenuated vaccines and nonliving or peptide vaccines with equal efficacy should remain the goal, as it is apparent that smallpox vaccine once again will become part of the vaccinologist's and public health official's armamentarium in the decades to come.

Duration of antiviral immunity after smallpox vaccination

Although naturally occurring smallpox was eliminated through the efforts of the World Health Organization Global Eradication Program, it remains possible that smallpox could be intentionally released. Here we examine the magnitude and duration of antiviral immunity induced by one or more smallpox vaccinations. We found that more than 90% of volunteers vaccinated 25-75 years ago still maintain substantial humoral or cellular immunity (or both) against vaccinia, the virus used to vaccinate against smallpox. Antiviral antibody responses remained stable between 1-75 years after vaccination, whereas antiviral T-cell responses declined slowly, with a half-life of 8-15 years. If these levels of immunity are considered to be at least partially protective, then the morbidity and mortality associated with an intentional smallpox outbreak would be substantially reduced because of pre-existing immunity in a large number of previously vaccinated individuals.

Effect of Fc-receptor modulation on mumps-virus-dependent lymphocyte-mediated cytotoxicity in vitro

The natural cytotoxicity of peripheral blood lymphocytes (PBL) from normal human donors to a variety of tissue culture target cells increases upon brief exposure of lymphocytes to mumps virus. The effector cells operative in this system have Fc receptors for IgG (FcR), since cytotoxicity was abolished when FcR+ cells were removed by passage of the lymphocyte over immune-complex columns. When PBL were treated with immune complexes for 16 h at 37 degrees C, their FcR activity was sharply decreased (modulation), as indicated by a significantly reduced capacity of the treated cells to display antibody-dependent cytotoxicity (ADCC). Modulation had variable effects on natural cytotoxicity. In contrast, the virus-dependent cytotoxicity above the natural cytotoxicity remained essentially unchanged, indicating that a functionally intact FcR is not required in this system for carrying out cytolysis.

Vaccinia virus-specific CD8+ cytotoxic T lymphocytes in humans

Stimulation of human vaccinia virus immune peripheral blood mononuclear cells in vitro from vaccinia virus-immune donors with live vaccinia virus-infected autologous cells generated vaccinia virus-specific cytotoxic T lymphocytes (CTL) capable of lysing vaccinia virus-infected cells. We generated vaccinia virus-specific CD8+ clones and CD4+ CTL lines by limiting dilution from two donors by using peripheral blood mononuclear cells obtained 2 months or 4 years postrevaccination with vaccinia virus. These results demonstrate that vaccinia virus-specific CTL are generated as a result of immunization of humans with vaccinia virus and that both CD8(+)- and CD4(+)-specific T cells are maintained as memory cells.

Vaccinia virus-specific human CD4+ cytotoxic T-lymphocyte clones

Vaccinia virus-specific cytotoxic T-lymphocyte (CTL) clones were established from a healthy donor, who had been immunized with vaccinia virus vaccine, by stimulation of peripheral blood lymphocytes with UV-inactivated vaccinia virus antigen. The phenotype of all of the clones established was CD3+ CD4+ CD8- Leu11-. We used a panel of allogenic vaccinia virus-infected B-lymphoblastoid cell lines and demonstrated that some of the clones recognized vaccinia virus epitopes presented by human leukocyte antigen (HLA) class II molecules. Monoclonal antibodies specific for either HLA-DP or HLA-DR determinant reduced the cytotoxicity of specific clones. The HLA-restricted cytotoxicity of the clones is vaccinia virus specific, because vaccinia virus-infected but not influenza virus-infected autologous target cells were lysed. Using vaccinia virus deletion mutants, we found that some of the CTL clones recognize an epitope(s) that lies within the HindIII KF regions of the vaccinia virus genome. These results indicate that heterogeneous CD4+ CTL clones specific for vaccinia virus are induced in response to infection and may be important in recovery from and protection against poxvirus infections.

Poxvirus pathogenesis

Poxviruses are a highly successful family of pathogens, with variola virus, the causative agent of smallpox, being the most notable member. Poxviruses are unique among animal viruses in several respects. First, owing to the cytoplasmic site of virus replication, the virus encodes many enzymes required either for macromolecular precursor pool regulation or for biosynthetic processes. Second, these viruses have a very complex morphogenesis, which involves the de novo synthesis of virus-specific membranes and inclusion bodies. Third, and perhaps most surprising of all, the genomes of these viruses encode many proteins which interact with host processes at both the cellular and systemic levels. For example, a viral homolog of epidermal growth factor is active in vaccinia virus infections of cultured cells, rabbits, and mice. At least five virus proteins with homology to the serine protease inhibitor family have been identified and one, a 38-kDa protein encoded by cowpox virus, is thought to block a host pathway for generating a chemotactic substance. Finally, a protein which has homology with complement components interferes with the activation of the classical complement pathway. Poxviruses infect their hosts by all possible routes: through the skin by mechanical means (e.g., molluscum contagiosum infections of humans), via the respiratory tract (e.g., variola virus infections of humans), or by the oral route (e.g., ectromelia virus infection of the mouse). Poxvirus infections, in general, are acute, with no strong evidence for latent, persistent, or chronic infections. They can be localized or systemic. Ectromelia virus infection of the laboratory mouse can be systemic but inapparent with no mortality and little morbidity, or highly lethal with death in 10 days. On the other hand, molluscum contagiosum virus replicates only in the stratum spinosum of the human epidermis, with little or no involvement of the dermis, and does not spread systemically from the site of infection. The host response to infection is progressive and multifactorial. Early in the infection process, interferons, the alternative pathway of complement activation, inflammatory cells, and natural killer cells may contribute to slowing the spread of the infection. The cell-mediated response involving learned cytotoxic T lymphocytes and delayed-type hypersensitivity components appears to be the most important in recovery from infection. A significant role for specific antiviral antibody and antibody-dependent cell-mediated cytotoxicity has yet to be demonstrated in recovery from a primary infection, but these responses are thought to be important in preventing reinfection.

Poxvirus pathogenesis

Poxviruses are a highly successful family of pathogens, with variola virus, the causative agent of smallpox, being the most notable member. Poxviruses are unique among animal viruses in several respects. First, owing to the cytoplasmic site of virus replication, the virus encodes many enzymes required either for macromolecular precursor pool regulation or for biosynthetic processes. Second, these viruses have a very complex morphogenesis, which involves the de novo synthesis of virus-specific membranes and inclusion bodies. Third, and perhaps most surprising of all, the genomes of these viruses encode many proteins which interact with host processes at both the cellular and systemic levels. For example, a viral homolog of epidermal growth factor is active in vaccinia virus infections of cultured cells, rabbits, and mice. At least five virus proteins with homology to the serine protease inhibitor family have been identified and one, a 38-kDa protein encoded by cowpox virus, is thought to block a host pathway for generating a chemotactic substance. Finally, a protein which has homology with complement components interferes with the activation of the classical complement pathway. Poxviruses infect their hosts by all possible routes: through the skin by mechanical means (e.g., molluscum contagiosum infections of humans), via the respiratory tract (e.g., variola virus infections of humans), or by the oral route (e.g., ectromelia virus infection of the mouse). Poxvirus infections, in general, are acute, with no strong evidence for latent, persistent, or chronic infections. They can be localized or systemic. Ectromelia virus infection of the laboratory mouse can be systemic but inapparent with no mortality and little morbidity, or highly lethal with death in 10 days. On the other hand, molluscum contagiosum virus replicates only in the stratum spinosum of the human epidermis, with little or no involvement of the dermis, and does not spread systemically from the site of infection. The host response to infection is progressive and multifactorial. Early in the infection process, interferons, the alternative pathway of complement activation, inflammatory cells, and natural killer cells may contribute to slowing the spread of the infection. The cell-mediated response involving learned cytotoxic T lymphocytes and delayed-type hypersensitivity components appears to be the most important in recovery from infection. A significant role for specific antiviral antibody and antibody-dependent cell-mediated cytotoxicity has yet to be demonstrated in recovery from a primary infection, but these responses are thought to be important in preventing reinfection.

The immune response to vaccinia virus infection in mice: analysis of the role of antibody

Immune response to primary intraperitoneal infection with vaccinia virus (strain IHD-J) was studied in C3H/Hej mice. Antibodies reactive with virus structural proteins were detected 6 days and neutralizing antibodies 8 days after infection. Although serum antibodies from infected mice bound to vaccinia virus infected cells, these antibodies were ineffective in complement mediated lysis of infected cells and were only moderately active in experiments with antibody dependent cellular cytotoxicity (ADCC). Immunoblotting analysis showed that serum antibody reacted with a number of structural proteins of both intracellular and extracellular forms of vaccinia virus. Immunoprecipitation results showed antibody binding of nonstructural proteins and glycoproteins. Correlation of the kinetics of NK and CTL activities in infected mice with neutralizing antibodies indicated that the cellular functions clearly precede the appearance of serum neutralizing antibody. The resolution of primary infection in mice thus appears to be mediated by functions of cellular immunity while resistance to reinfection may be dependent on circulating neutralizing antibody.

Natural cytotoxicity in immunodeficiency diseases: preservation of natural killer activity and the in vivo appearance of radioresistant killing

We studied spontaneous natural killer (NK) cell activity and radiation-resistant NK mediated cytotoxicity in four patients with clinically documented severe combined immune deficiency disease (SCID), and in one subject each with intestinal lymphangiectasia and cartilage-hair hypoplasia. We observed the preservation of spontaneous NK activity in all patients despite the presence of profound B- and T-lymphocytopenia and clinical immunodeficiency. NK activity was associated with relatively normal circulating numbers of OKM1+ lymphocytes, a population known to contain NK effectors. Spontaneous NK activity resistant to 3000 rad was increased in all patients, indicating the presence of activated natural killer cells in vivo. The concept of a chronically activated immune system in these patients was further supported by the presence of increased Ia positive T cells in all subjects tested, suggesting that radioresistant NK activity may be a useful parameter to measure when assessing in vivo immune activation. Our data, as well as that of others, supports the hypothesis that at least one population of NK cells is a distinct lineage arising at the differentiation level of myeloid and lymphoid stem cells in the bone marrow.

Cell-mediated cytotoxicity of bovine mononuclear cells to IBRV-infected cells: dependence on Sephadex G-10 adherent cells

Following intranasal inoculation of cattle with infectious bovine rhinotracheitis virus (IBRV) mononuclear cells that produced a genetically unrestricted cytotoxic response against IBRV-infected, but not against uninfected cells, were present in peripheral blood. Cytotoxicity was detected between 6 and 14 days after primary infection in a 20 h, but not in a 5 h, 51Cr-release assay. Cytotoxic activity was present in peripheral blood mononuclear cells from infected and subsequently hyperimmunized cattle for a considerably longer time. Neither natural cytotoxicity, antibody-dependent cell cytotoxicity, nor antibody produced during the assay was responsible for the cytotoxicity. However, cytotoxicity was dependent upon an adherent mononuclear cell that was partially removed by passage over nylon wool and completely removed by passage over Sephadex G-10.

Cytotoxic lymphocytes generated in vivo with acute measles virus infection

We studied the generation of cytotoxic lymphocytes in adults during an outbreak of acute measles virus infection. Nine patients were studied determining in particular whether virus-specific cytotoxic T lymphocytes could be directly detected in peripheral blood during this acute infection. The cytotoxicity of PBL was assayed against measles virus-infected and uninfected phytohemagglutinin-induced blast cells of matched and mismatched HLA, A, B, and C types, in a standard 4-h 51Cr release assay. There was greater cytotoxicity against measles virus-infected than uninfected target cells in at least one sample from every patient. In 4 patients this preferential lysis of virus infected cells was greater (a difference of more than 10% virus-specific lysis) against HLA-matched than mismatched targets. This preference for HLA A and B matched infected target cells was also clearly seen when the effector PBL were depleted of FC receptor bearing cells. The other 5 subjects exhibited no evidence of preferential lysis of HLA-matched measles virus-infected cells. All 9 patients limited the spread of measles virus infection and recovered equally from the acute infection. These studies provide some evidence to suggest that MHC-restricted virus-specific CTL are detectable in human peripheral blood during acute measles virus infection, albeit only with low frequency, but are not necessarily associated with recovery from disease.

Impaired culture generated cytotoxicity with preservation of spontaneous natural killer-cell activity in cartilage-hair hypoplasia

Recent studies of cartilage-hair hypoplasia (CHH), a form of short-limbed dwarfism, have shown that all affected individuals have a cellular proliferation defect that results in a cellular immunodeficiency. However, only a minority of CHH individuals suffer from severe, life-threatening infections. For this reason, relevant immune defense mechanisms that may be responsible for maintaining intact host defenses in the majority of CHH individuals were studied. Spontaneous and allogeneic culture-induced (mixed lymphocyte response-MLR) specific and nonspecific (NK-like) cytotoxic mechanisms were analyzed and correlated with lymphocyte subpopulations present in CHH and normal individuals. Spontaneous natural-killer (NK) activity was present at or above normal levels, but culture-induced specific cytotoxicity and NK-like cytotoxicity as well as NK-like activity by T cell lines were significantly reduced in CHH individuals. The generation of radiation-resistant cytotoxicity, which normally occurs during allogeneic MLR, was markedly diminished in CHH, and was correlated with the decreased proliferation observed in CHH cultures. Preservation of spontaneous NK activity and loss of all forms of culture-induced cytotoxicity was associated with an increase in the proportion of lymphocytes bearing a thymic independent NK phenotype (OKM1+ OKT3- Fc gamma + low-affinity E+), and a significant decrease in thymic derived OKT3+ cytolytic T cell sub-populations in CHH individuals. Therefore, an intact cellular cytotoxic effector mechanism has been identified in CHH (i.e., NK activity). Natural cytotoxicity may be of importance in maintaining host resistance to viral infections despite diminished thymic-derived effector mechanisms in cartilage-hair hypoplasia.

Characterization of the human peripheral blood effector cells mediating antibody-dependent cell-mediated cytotoxicity against respiratory syncytial virus

Peripheral blood lymphocytes were separated into several subpopulations and evaluated for their ability to mediate antibody-dependent cell-mediated cytotoxicity (ADCC) against respiratory syncytial virus (RSV)-infected HeLa cells. Using erythrocyte rosetting methods, nylon wool filtration, and cytolysis with OKT-3 monoclonal antibody, two lymphocyte subpopulations were shown to mediate RSV-ADCC; non-T, non-B, and IgG-Fc receptor-bearing lymphocytes and E-rosetting cells with IgGFc receptors (T gamma cells). Removal of phagocytic cells did not alter ADCC activity. Monoclonal antibody to human NK and K cells, HNK-1, recognized these two lymphocyte effector subpopulations.

The interaction of cells persistently infected with canine distemper virus with antiviral antibody and complement

Cells persistently infected with canine distemper virus can be lysed by antibody and complement. This reaction is dependent upon the alternative complement pathway. In the absence of antiviral antibody, the virus-infected cells will activate the alternative complement pathway, although this will not produce cell lysis.

Evidence for granulocyte-mediated macrophage activation after C. parvum immunization

It has been previously demonstrated that at the peak of the peritoneal response to Corynebacterium parvum (Day 4), cytolytic macrophages can be characterized by the presence of intracellular bacteria. In the present study, the role of neutrophils in the activation of peritoneal macrophages by C. parvum was investigated. Inflammatory neutrophils isolated 5 hr after ip administration of C. parvum were transferred to normal, syngeneic mice and the peritoneal macrophages of recipients harvested 4 days later were tested for cytoxicity against HeLa cells. Neutrophils isolated from mice 5 hr after C. parvum immunization were effective in inducing cytolytic macrophages. Less than 100-fold as much bacteria was needed to induce comparable levels of cytotoxic activity when introduced inside granulocytes. Neutrophils obtained from mice 48 hr after C. parvum injection or mononuclear cells were not good macrophage activators. Viable neutrophils were not required as freeze-thawed cells were able to activate macrophages in recipient mice. The intracellular distribution of C. parvum changed dramatically with time. Initially almost all bacteria were found within neutrophils. By 24 hr, many macrophages contained either bacteria or granulocytes which had ingested C. parvum. Pyridine extracts of C. parvum, which do not activate peritoneal macrophages when injected directly into mice, did not induce neutrophils capable of activating macrophages. The residue of pyridine-extracted C. parvum did induce neutrophils that could activate macrophages when transferred. The results suggest that processing of the bacteria by inflammatory granulocytes may be an obligatory step in macrophage activation by this agent. The peak response occurred earlier than T-cell immunity is usually observed and it is suggested that direct activation of macrophages via ingestion of neutrophils may represent the earliest stage of macrophage activation by C. parvum.

Lysis of allogeneic human lymphocytes by nonspecifically activated T-like cells

In the generation of cytotoxic effector cells specific for influenza A virus-infected lymphocytes, three donors have given an unusual pattern of lytic activity, killing HLA-mismatched target cells. This has been analyzed in detail for one donor and one of the other two shows similar results. Activation only requires culture in medium between 1 and 4 days and parallels development of cell line K562-directed natural killer cells. Target lymphocytes do not need to be virus-infected and appear to be normal lymphocytes. The effector cells carry the surface markers T3 and T8 defined by OKT3/anti-Leu4 and OKT8/anti-Leu2a monoclonal antibodies, respectively. Unlike HLA class 1-restricted or -directed cytotoxic T cells, neither anti-Leu2a/nor anti-Leu4 blocked killing in the absence of complement. MHM23, a monoclonal antibody specific for the human lymphocyte function antigen, blocked lysis. The results indicate that these effector cells are related to cytotoxic T lymphocytes, but can lyse allogeneic target cells through a different recognition process. There is some specificity because autologous cells were not killed.

Case for adoptive immunotherapy in cancer

Patients with normal immune systems may be unable to mount effective defences against solid tumours because of (1) the generation of suppressor T cells in the low zone tolerance response elicited by the low concentrations of antigen furnished by slow growing solid tumours; (2) the ineffectiveness of the cytolytic T-cell response when the tumour cell membrane lacks the major histocompatibility gene products required for linkage to tumour antigens; and (3) the hindrance of antibody-dependent cellular cytotoxicity by antitumour antibodies when the precise requirements for the reaction cannot be fulfilled in the sites occupied by solid tumours. Recent immunological advances suggest that it should be possible to isolate antigens from cancer cells, produce antibodies against these antigens, bind the antibodies to the patient's macrophages and K lymphocytes, and reinject the bound cells into the patients to stimulate lymphokine synthesis and antibody-dependent cellular cytoxicity.

Activation of Fc receptor-bearing lymphocytes by immune complexes. II. Killer lymphocytes mediate Fc ligand-induced lymphokine production

Cells that participate in immune complex-induced production of leukocyte migration inhibitory factor (LIF) activity can be concentrated in a population making up 2-4% of human peripheral blood lymphocytes in which greater than 90% of the cells are active in a single cell antibody-dependent cellular cytotoxicity assay. When so concentrated, such killer (K) cell preparations are as efficient in producing LIF activity as mitogen activated T lymphocytes. Other Fc receptor (FcR)-bearing lymphocytes, including natural killer (NK) cells, do not produce measurable LIF activity when incubated with immune complexes (additional evidence that the K and NK cells among ligands to the FcR of the appropriate lymphocytes, possibly without need for exogenous receptor bridging, is the only requirement for their activation to immune complex-induced lymphokine production (ICLP). It is probable that ICLP by K cells palays a role in antibody-mediated effector functions in vivo.

In vitro generation of human cytotoxic lymphocytes by virus. Viral glycoproteins induce nonspecific cell-mediated cytotoxicity without release of interferon

Purified hemagglutinin and fusion glycoproteins of measles virus either in soluble form or inserted in artifical membranes bind to human peripheral blood lymphocytes and induce cell-mediated cytotoxicity (CMC) in a dose-response fashion. Both autologous and heterologous noninfected target cells are lysed in vitro. The expression of CMC is not inhibited by anti-measles virus antibody added to lymphocytes previously exposed to viral glycoproteins. THe killer lymphocytes are Fc receptor positive, both erythrocyte-rosetting and non-erythrocyte-rosetting, as assessed by both positive and negative selection experiments. The induction of nonspecific CMC by viral glycoproteins either in the soluble state or inserted into artificial membranes could be segregated from the CMC associated with whole virions. First, on kinetics studies, purified viral glycoproteins induced CMC more rapidly than did whole virus. Second, viral glycoprotein-produced response occurred in the absence of detectable release of interferon into the culture medium, whereas CMC activity due to whole virions was associated with interferon release. The fact that purified measles virus glycoproteins integrated into artificial membrane bilayers were as efficient as their soluble counterparts in inducing CMC suggests that the hydrophobic portion of the glycoproteins was not involved in the induction and expression of the lytic activity. Purified glycoproteins from lymphocytic choriomeningitis virus behave similarly, although this virus is unrelated to measles virus. It is inferred that interferon-independent CMC induced by viral glycoproteins might account for some of the biological reactions occurring early in the control of a viral infection.

Absence of a correlation between humoral and cellular responses to a vaccinia virus and products of the major histocompatibility complex in rhesus monkeys

Sixty-two Rhesus monkeys were tested at different times after vaccinia virus infection for virus-specific induction of lymphocyte proliferation in vitro or antibody production in vivo. No association was found between identifiable RhLA-controlled antigens and the strength of the cellular proliferative and/of humoral response.

Studies on the role of humoral and cell-mediated immunity in pigs after vaccination with Aujeszky's disease virus

Humoral and cellular immunity in pigs vaccinated twice with Aujeszky's disease virus (ADV) was studied by seroneutralizing test and direct leucocyte migration inhibition technique. Significant migration inhibition of leucocytes (LMI) was found on the fifth day, whereas specific antibodies began to appear at that time only in very low titers. Anamnestic reaction due to the second injection of ADV did not bring about a significant increase of migration inhibition of leucocytes, instead the level of antibodies elevated markedly.

Cytotoxic cells induced during lymphocytic choriomeningitis virus infection of mice: natural killer cell activity in cultured spleen leukocytes concomitant with T-cell-dependent immune interferon production

The characteristics and specificities of spleen and peritoneal cytotoxic cells generated during lymphocytic choriomeningitis virus (LCMV) infection of C3H/St mice were examined. Activated natural killer (NK) cell activity was identified in fresh leukocyte populations from the 2nd to 8th days postinfection, whereas virus-specific cytotoxic T-cell activity was detected from the 6th to 14th days. When leukocytes were cultured overnight at 37 degrees C before assay, T-cell activity was still observed, but nonspecific activated NK cell-like cytotoxicity was only detected on the 6th and to a lesser degree the 8th day postinfection. Overnight culture of leukocytes taken earlier in the infection eliminated their NK cell activity. Similar activities were seen with spleen cell, plastic-adherent peritoneal cell, and nonadherent peritoneal cell populations. The virus-specific cytotoxicity observed with adherent peritoneal cells was due to contamination with cytotoxic T cells, as shown by H-2-restricted cytotoxicity and sensitivity to anti-theta antibody and complement. The nonspecific cultured day 6 effector cell from either the spleen or peritoneum displayed killing specificities and other physical properties identical to those of activated NK cells, but had sensitivities to anti-theta antibody and complement intermediate between activated day 3 NK cells and cytotoxic T cells. Culture stable NK-like cells were not found in athymic nude mice, suggesting a T-cell-dependent mechanism. Whereas LCMV spleen homogenates contained 10-fold-higher levels of interferon at day 2 than at day 6 postinfection, substantially more (nearly 20-fold) interferon was made in cultures of day 6 cells than day 2 cells. Spleen interferon was predominantly type I, whereas the culture interferon was predominantly type II, as shown by acid lability studies. Significant levels of interferon were produced by nylon-wool-passed day 6 spleen cells, and virtually all interferon production was eliminated by treatment of either day 2 or day 6 cells with antibody to theta antigen and complement, suggesting that T cells produced the interferon in vitro. Furthermore, athymic nude mice had no culture-stable NK cells 6 days postinfection, and spleen cells from them failed to produce significant levels of interferon in vitro. Addition of interferon (type I, fibroblast) to cultured C3H spleen cells affect the already elevated levels of cytotoxicity in day 6 cultures, suggesting that the NK cells in the day 6 culture were already activated. Our results suggest that T cells responding to LCMV infection secrete interferon type II which causes the continued activation of NK cells in culture. The resulting population of activated NK cells therefore appears to be relatively stable in culture and to express more theta antigen because of this T-cell dependence. Although one could mistakenly or allospecific cytotoxic T cells or cytotoxic macrophages, more careful examination shows that they are most likely activated NK cells...

Immune response in rabbits to surface components of extracellular and intracellular forms of vaccinia virus

The development of cellular as well as humoral immune response to extracellular and intracellular forms of vaccinia virus (ECV and ICV, respectively) and their surface antigens were studied in rabbits. Direct lymphocyte cytotoxicity and peripheral blood leukocyte migration inhibition tests were used to measure cell-mediated immune response, while neutralizing and hemagglutination-inhibiting antibodies were assayed for measuring humoral immune response. Direct cytotoxicity of lymphocytes from rabbits immunized with ECV or its surface proteins was demonstrable by day 7 after immunization, and by the end of week 3 it almost declined to pre-immunization levels. Inoculation with ICV or its surface proteins failed to induce lymphocyte cytotoxicity. In contrast, migration inhibition of peripheral blood leukocytes from rabbits immunized with ECV, ICV, or their surface proteins was observed with homologous antigens. However, leukocytes from rabbits immunized with ECV or its surface proteins also showed migration inhibition in the presence of ICV. Similarly, in the humoral immune response, neutralizing antibodies were produced against homologous as well as heterologous forms of virus despite immunization with purified preparations of ECV, ICV, or their surface proteins. Adsorption with purified ICV preparations abolished the neutralizing activity of these antisera against heterologous forms of virus. Hemagglutination-inhibiting antibodies, on the other hand, were produced only after immunization with ECV or its surface proteins. In addition, antibody-dependent cell-mediated cytotoxicity was employed to detect specific antibody response after immunization of rabbits with live virus, ECV, and ICV. Antisera raised against ECV or live virus supported antibody-dependent cell-mediated cytotoxicity, whereas ICV-antiserum failed to do so. The antibody activity present in the former antisera was abolished by absorption with cell membranes from vaccinia-infected cells but not with purified ICV. The data suggest that immunization with inactivated ECV seems to bring about interaction between host immune response (cellular and humoral) and virus-infected cells, which may, perhaps, be necessary for protection against pox virus infection. A similar interaction is unlikely to occur after immunization with inactivated ICV.

Hamster T cells participate in MHC alloimmune reactions but do not effect virus-induced cytotoxic activity

The participation of hamster T cells in a variety of putative MHC-determined reactions was studied utilizing a well-characterized, highly selective goat anti-hamster thymocyte (G alpha HT) serum. Hamster lymphoid cell suspensions treated with G alpha HT lose much of their capacity to induce local graft-versus-host reactions and to function as responder cells in mixed lymphocyte reactions. In contrast to the participation of hamster T cells in alloimmune reactions (MLR and GVHR), virus-induced, cytotoxic activity in hamsters undergoing acute virus infection is not T-cell-mediated. This latter finding was rather surprising in view of the major role played by cytotoxic T effector cells in comparably infected mice and rats. These results suggest that, although hamsters are able to respond to putative class II MHC disparities in allogeneic reactions, MHC-encoded molecules, presumably class I, are not utilized for induction of effective cytotoxic activity in response to acute virus infection in this species. The implications of these findings are discussed in relation to our present understanding of the hamster MHC.

Natural and immune cytolysis of canine distemper virus-infected target cells

Natural and immune cytolysis of canine distemper virus (CDV)-infected target cells in vitro is described. Lymphocytes expressing natural cytotoxicity were found in specific-pathogen-free beagle dogs and in beagle-coonhound crosses before vaccination with CDV and indefinitely after vaccination, when the ephemeral immune lymphocyte-mediated cytotoxicity (ILMC) had declined. In contrast to the natural lymphocyte-mediated cytotoxicity, the ILMC was genetically restricted, could not be blocked by CDV-specific antibody, and was effective against measles virus-infected as well as CDV-infectd target cells. Lymphocyte populations were depleted of Fc receptor and surface immunoglobulin-bearing cells by rosetting techniques and tested in comparison. An antibody-dependent cell-mediated cytotoxicity was demostrated against CDV-infected target cells that were preincubated with CDV antibody when Fc receptor-bearing lymphocytes were not removed. The ILMC was measurable for approximately 10 days beginning at 6 days post-vaccination. In contrast, CDV antibody measured by virus neutralization and humoral cytotoxicity was detectable by 6 days postvaccination and persisted at peak levels for at least 5 months.

Immune response to acute virus infection in the Syrian hamster. I. Studies on genetic restriction of cell-mediated cytotoxicity

Syrian hamsters show evidence of classical T-cell-mediated immune reactivity to acute virus infection as judged by primary foot pad swelling, kinetics of in vitro cytotoxic activity, and virus specificity of cytotoxic effector cells. In spite of this, no evidence of genetic restriction is observed among the variety of allodisparate inbred strains tested. This virus-induced, cell-mediated killing extends across strain barriers despite strong cellular and serologic alloreactivity among some of the strains utilized. To account for the apparent lack of genetic restriction, we currently favor the hypothesis that all hamsters examined thus far share at least one class I MHC antigen. Since these animals differ at hamster loci which elicit MLR, GVHR, acute SGR, CML, and alloantibody, we presume class II MHC polymorphism exists in this species. The presence of putative class II MHC polymorphism without detectable class I polymorphism is unusual among mammals examined to date, and of unknown biologic significance.

Antibody-mediated destruction of virus-infected cells

This chapter describes the effect of antibody on virus-infected cells with special reference to the human system. The destruction by antibody of the infected cells through the mediation of complement is described in detail based in considerable part on the contributions of the authors. Activation of the alternative pathway by the various infected cells is of special interest. The interesting effect of the antibody-dependent cell-mediated cytotoxicity (ADCC) system involving viral antigens in cell killing is also presented. Multiple additional topics are also covered, such as the effect of antibody on the expression of viral proteins both on the surface of the cell and intracellularly. Serum antibody, produced in response to virus infections, is of major importance in preventing the spread of infection by virtue of neutralizing free virus in extracellular fluids. Virus neutralization by antibody is enhanced by complement. Antibody binding to the surface of virus-infected cells can affect virus production and release in the absence of an effector system. Immunoglobulin (IgG) antibody can mediate the destruction of virus-infected cells in conjunction with complement or cytotoxic lymphocytes. In addition, at a conceptual level there is evidence to suggest that antibody may enhance and confer specificity on basic nonspecific humoral and cell-mediated defense mechanisms.

Cell-mediated cytotoxicity during vaccinia virus revaccination in man: influence of antibodies and interferon

Seven healthy human adults were revaccinated with vaccinia virus. Cell-mediated cytotoxicity to vaccinia virus-infected fibroblasts was investigated on the day of vaccination and on days with peak activity. Three donors were studied until day 30 after vaccination. The addition of interferon to cytotoxicity reactions resulted in an increase in killing. This increase was not seen when antibodies were added. When a mixture of lymphocytes from a revaccinated and a non-revaccinated donor was used as effector cells, the killing observed corresponded to the killing seen with lymphocytes from the revaccinated donor, when tested alone. This finding indicates that no antibodies or other soluble mediators capable of increasing cytotoxicity are released from the lymphocytes during the cytotoxicity assay.

Antibody-dependent cell-mediated cytotoxicity (ADCC) in Aujeszky's disease

Antibody-dependent cell-mediated cytotoxicity (ADCC) was studied using as targets 51Cr-labelled Vero cells infected with the Bartha strain of Aujeszky's disease virus (ADV). Using hyperimmune anti-ADV serum to sensitize the targets, porcine leukocytes from dextran-sedimented blood were found to be efficient effector cells yielding maximal 51Cr release by 16 hours. Whilst complement-dependent cytotoxic antibody could be demonstrated no enhancement of ADCC by complement was found. The sera of pigs vaccinated i.m. with Bartha virus were titrated in ADCC using leukocytes as effector cells and the results compared with those obtained by virus neutralization. ADCC proved to be a much more sensitive technique and might, therefore, provide the basis for a reliable diagnostic test. Partially purified lymphocytes and polymorphonuclear leukocytes from blood and peritoneal exudates, and macrophages from exudates were found to mediate ADCC with hyperimmune serum, but differences were observed in the efficiency and timing of their cytotoxic effects.

Induction and kinetics of natural killer cells in humans following interferon therapy

Natural killer (NK) cells are non-B, non-T lymphocytes that effect spontaneous cytolysis of both virus-infected and neoplastically transformed target cells. These NK lymphocytes have been detected in several species including man. Interferon is a primary regulator of natural killer activity. Because NK cells have been implicated in the regulation of tumour cell expression and can be induced by interferon in murine models, we have studied patients receiving large doses of interferon to determine (1) whether interferon could induce NK lymphocytes in the peripheral blood of man, and (2) whether there are characteristic kinetics for the appearance, disappearance and reactivation of NK lymphocytes following interferon therapy. We report here the activation of human NK cells by the systemic inoculation of human subjects with interferon. Five patients received interferon as therapy for non-Hodgkin's lymphoma. All showed a marked increase in NK cell activity 12--24 h after inoculation. Peak NK activity occurred 18 h after introducing interferon, and thereafter declined rapidly but remained above pre-interferon levels. Induced NK activity occurred with reintroduction of interferon but at lower levels of activity and with different kinetics.

Cell cytotoxicity due to specific influenza antibody production in vitro after recent influenza antigen stimulation

Peripheral blood leukocytes, obtained from volunteers after vaccination or natural illness with influenza, were assayed for cytotoxicity against influenza virus-infected cells. Approximately 7 days after vaccination or the onset of respiratory illness, peak cytotoxicity was demonstrated in a chromium-release assay. Secretion of specific antibody against hemagglutinin from the leukocytes during in vitro incubation was demonstrated in quantities that would mediate the cell cytotoxicity observed. Antibody secretion was inhibited by exposure to cycloheximide but not by exposure to trypsin. The secretion of antibody against hemagglutinin from peripheral blood leukocytes occurred only at the time of maximal cytotoxicity. We thus demonstrate secretion of specific antibody in vitro after recent viral antigen stimulation. Moreover, this antibody is capable of conveying cytotoxic capacity to peripheral blood leukocytes that may be important in the recovery process from acute viral infection.

The in vitro cellular response of human lymphocytes to trinitrophenylated autologous cells: HLA-D restriction of proliferation but apparent absence of HLA restriction of cytolysis

Primary as well as secondary proliferative and cytotoxic responses to 2,4,6-trinitrophenyl (TNP)-modified autologous human cells have been studied. Proliferative responses have been obtained both by primary (peak on day 6) and secondary (peak on day 2--3) stimulation. Both responders and nonresponders were found among the panel of unrelated individuals tested. All responders in a secondary reaction also gave significant primary responses. Intrafamilial studies showed that the ability to restimulate a proliferative response followed the major histocompatibility complex haplotype of the responder; in some cases, the two haplotypes differed in their ability to restimulate. Using unrelated individuals typed for HLA-A, B and C, as well as HLA-D and DR, proliferation was shown to occur only when the unrelated stimulator shared HLA-D region products with the responder. In contrast, no HLA restriction was found in cell-mediated lympholysis (CML) (neither in primary nor in secondary responses) in most cases. The data suggest that the observed killing is independent of sensitization. Both responders and nonresponders in proliferation yielded high levels of lysis; no increase of lysis was found in kinetic studies; most allogeneic CML combinations were highly lytic for the TNP-modified responder cells at a time when the lysis of the specific allogeneic target is negligible. These preliminary data suggest that the killing observed might be different from classical T cell-mediated lympholysis.

Demonstration of HLA restricted killer cells in patients with acute measles

The relationship between HLA determinants on effector and target cells and cell-mediated cytotoxicity was studied using the release of 51Cr from measles virus-infected PHA-blasts. HLA compatibility between effector and target cells was not required if effector lymphocytes were derived from measles seropositive adults, from a patient with SSPE, and from children after live measles vaccination. Cytotoxicity was always abolished after removal of Fc receptor-bearing lymphoid cells. In these donors, the effect is, therefore, probably due to K cells. In contrast, lymphocytes from children with acute measles preferentially killed those virus-infected target cells with which they shared HLA antigens. Selective lytic activity was still observed after elimination of Fc receptor-bearing lymphoid cells. It is suggested that HLA-dependent killer cells represent specific cytotoxic T lymphocytes. These cells seem to be limited to the acute phase of measles.

Cell-mediated cytotoxicity following influenza infection and vaccination in humans

Cell-mediated cytotoxic activity in circulating mononuclear cells from 31 volunteers challenged with live influenza A/Victoria virus, and 22 volunteers vaccinated with inactivated influenza vaccine, was examined employing target cells infected with several viruses by means of a 51Cr release assay. Effectors from infected volunteers, and from volunteers who manifested four-fold rises in serum HAI antibody after vaccination, demonstrated significantly elevated levels of cytotoxicity against targets infected with the homologous virus. Elevated cytotoxicity was seen by days 3 and 4 after challenge or vaccination and returned to baseline levels by day 9 to 10. In infected volunteers, cytotoxic activity was broadly directed, rising against targets infected with an antigenically distinct virus within the same influenza type (A), against targets infected with a serologically unrelated virus of a different influenza type (B), and also against cells infected with Newcastle disease virus, a paramyxovirus from another species. However, elevated levels of cytotoxicity were not observed when targets infected with herpes simplex virus, a member of an entirely different virus group, or when uninfected target cells were employed. In vaccinated volunteers, the rise in cytotoxicity was more restricted than after infection, since elevated cytotoxic activity was seen only against cells infected with the homologous virus and not against inflenza B-infected cells. Fractionation of mononuclear cell populations indicated that effector cell activity is associated with T-cell depleted fractions and can only partially be reduced by depletion of adherent cells. The rapid development, short duration, and broadly directed specificity of this cytotoxic response suggest that it may be involved in early events following acute influenza infection in humans.