The immune response to influenza infection

Carbohydrate biopolymers enhance antibody responses to mucosally delivered vaccine antigens

We have evaluated the ability of two carbohydrate biopolymers, chitosan and gellan, to enhance antibody responses to subunit influenza virus vaccines delivered to the respiratory tracts of mice. Groups of mice were vaccinated three times intranasally (i.n.) with 10 microg of purified influenza B/Panama virus surface antigens (PSAs), which consist of hemagglutinin (HA) and neuraminidase (NA), either alone or admixed with chitosan or gellan solutions. Separate groups were vaccinated subcutaneously (s.c.) with PSAs adsorbed to Alhydrogel or chitosan or gellan alone i.n. Serum antibody responses were determined by enzyme-linked immunosorbent assay (ELISA) for influenza virus-specific immunoglobulin G (IgG) and by HA inhibition (HAI) and NA inhibition (NAI) assays. The local respiratory immune response was measured by assaying for influenza virus-specific IgA antibody in nasal secretions and by enumerating nasal and pulmonary lymphocytes secreting IgA, IgG, and IgM anti-influenza virus-specific antibodies by enzyme-linked immunospotting (ELISPOT). When administered alone i.n., B/Panama PSA was poorly immunogenic. Parenteral immunization with B/Panama PSA with Alhydrogel elicited high titers of anti-B/Panama antibodies in serum but a very poor respiratory anti-B/Panama IgA response. In contrast, i.n. immunization with PSA plus chitosan stimulated very strong local and systemic anti-B/Panama responses. Gellan also enhanced the local and serum antibody responses to i.n. PSA but not to the same extent as chitosan. The ability of chitosan to augment the immunogenicity of influenza vaccines given i.n. was confirmed using PSA prepared from an influenza A virus (A/Texas H1N1).

Alveolar epithelial cell chemokine expression triggered by antigen-specific cytolytic CD8(+) T cell recognition

CD8(+) T lymphocyte responses are a critical arm of the immune response to respiratory virus infection and may play a role in the pathogenesis of interstitial lung disease. We have shown that CD8(+) T cells induce significant lung injury in the absence of virus infection by adoptive transfer into mice with alveolar expression of a viral transgene. The injury is characterized by the parenchymal infiltration of host cells, primarily macrophages, which correlates with physiologic deficits in transgenic animals. CD8(+) T cell-mediated lung injury can occur in the absence of perforin and Fas expression as long as TNF-alpha is available. Here, we show that the effect of TNF-alpha expressed by CD8(+) T cells is mediated not exclusively by cytotoxicity, but also through the activation of alveolar target cells and their expression of inflammatory mediators. CD8(+) T cell recognition of alveolar cells in vitro triggered monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) expression in the targets, which was mediated by TNF-alpha. Antigen-dependent alveolar MCP-1 expression was observed in vivo as early as 3 hours after CD8(+) T cell transfer and depended upon TNF-R1 expression in transgenic recipients. MCP-1 neutralization significantly reduced parenchymal infiltration after T cell transfer. We conclude that alveolar epithelial cells actively participate in the inflammation and lung injury associated with CD8(+) T cell recognition of alveolar antigens.

Animal models of pulmonary infection in the compromised host: potential usefulness for studying health effects of inhaled particles

Pulmonary infection leading to pneumonia is a significant cause of morbidity and mortality worldwide. Airborne particles have been associated with pneumonia through epidemiological research, but the mechanisms by which particles affect the incidence of pneumonia are not well established. The purpose of this review is to examine the potential of animal models to improve our understanding of the mechanisms by which inhaled particles might affect the incidence and resolution of pulmonary infection. The pathogenesis of pneumonia in most animal models differs from that in humans because humans frequently have underlying diseases that predispose them to infection with relatively low doses of pathogens. Normal, healthy animals lack the underlying pathology often found in humans and clear bacteria and viruses rapidly from their lungs. To overcome this, animals are administered large inocula of pathogens, are treated with agents that cause mucosal lesions, or are treated with immunosuppressive drugs. Alternatively, pathogenic bacteria are protected from phagocytosis by encasing them in agar. No one animal model will replicate a human disease in its entirety, and the choice of model depends upon how well the animal infection mimics the particular human response being examined. The advantages and disadvantages of animal models in current use for bacterial and viral infections important in the etiology of human pneumonia are reviewed in detail. Considerable data indicate that prior exposure to particles compromises the ability of experimental animals to resolve a subsequent infection. In addition, information is available on the effects of particle exposure on various portions of respiratory defense including phagocytic function, ciliary movement, inflammation, and antibody response in the absence of infection. In contrast, little research to date has examined the consequences of particle exposure on the host defense mechanisms of animals already infected or on their ability to resolve their infection.

Antibody response to influenza immunization in two consecutive epidemic seasons in patients with renal diseases

The aim of this study was to assess antihemagglutinin and antineuraminidase antibody kinetics in 26 patients with renal diseases vaccinated against influenza in two consecutive epidemic seasons. Antibody responses were measured before immunization and 1, 3 and 6 months after immunization. Antihemagglutinin (HI) antibodies were determined by the hemagglutinin inhibition test and antineuraminidase (NI) antibody levels by the neuraminidase inhibition test. After vaccination HI and NI antibody titers significantly increased when compared with the pre-vaccination levels. Three months after vaccination the protection rates ranged from 50 to 61.5% in the 1995/96 season and 100% for all antigens in the 1996/97 season. Response rates ranged from 50 to 57.7% and 93.8 to 100% respectively. Significantly higher humoral response was recorded in the 1996/97 season than in the 1995/96 season. No serious adverse reactions were observed in the vaccinated patients and no symptoms of influenza or influenza-like infection were noted. In spite of some doubts about the safety and efficacy of influenza vaccination in patients from high-risk groups, the results of this study showed that many of them are able to produce HI antibodies in titers which are sufficient to protect against the influenza infection.

Humoral immune response to influenza vaccination in patients from high risk groups

Influenza is one of the most common respiratory diseases. Infections caused by this virus may be very serious and can lead to severe complications. So far, the most effective method of protection against influenza is annual vaccination. The Advisory Committee on Immunisation Practices recommends vaccination against influenza for some groups of people. Unfortunately, in spite of these clear indications, a large number of patients are not vaccinated. This article reviews the current scientific literature on immunological response to influenza vaccination in patients who are at especially high risk for serious post-influenza complications and for whom immunisation against this virus is strongly recommended. Results of studies carried out in Poland and other countries in elderly people, in patients with pulmonary diseases, renal diseases, diabetes mellitus, cancer and haemophilia, and in those with HIV infection are presented. In this review, we focus on the immune response to haemagglutinin. There are some discrepancies between the results of studies carried out by different authors in high risk groups of patients. Some investigations indicated poorer humoral response to influenza vaccine in these groups, while others showed responses comparable to those in healthy individuals. These differences may be explained by differences in types and stages of the chronic diseases, in the treatment and composition of influenza vaccines, and also patients' ages, vaccination history and prevaccination antibody titres. Influenza vaccines are well tolerated in high risk patients, and all adverse reactions are generally mild and similar to those observed in healthy people. Although, in some cases, immunological responses to influenza vaccination measured in the whole study group were poor, there were some individual patients who, after vaccination, developed antihaemaglutinin antibody titres which are considered to give protection against the infection or contribute to a milder course of the disease.

Viral escape by selection of cytotoxic T cell-resistant variants in influenza A virus pneumonia

Antigenic variation is a strategy exploited by influenza viruses to promote survival in the face of the host adaptive immune response and constitutes a major obstacle to efficient vaccine development. Thus, variation in the surface glycoproteins hemagglutinin and neuraminidase is reflected by changes in susceptibility to antibody neutralization. This has led to the current view that antibody-mediated selection of influenza A viruses constitutes the basis for annual influenza epidemics and periodic pandemics. However, infection with this virus elicits a vigorous protective CD8(+) cytotoxic T lymphocyte (CTL) response, suggesting that CD8(+) CTLs might exert selection pressure on the virus. Studies with influenza A virus-infected transgenic mice bearing a T cell receptor (TCR) specific for viral nucleoprotein reveal that virus reemergence and persistence occurs weeks after the acute infection has apparently been controlled. The persisting virus is no longer recognized by CTLs, indicating that amino acid changes in the major viral nucleoprotein CTL epitope can be rapidly accumulated in vivo. These mutations lead to a total or partial loss of recognition by polyclonal CTLs by affecting presentation of viral peptide by class I major histocompatibility complex (MHC) molecules, or by interfering with TCR recognition of the mutant peptide-MHC complex. These data illustrate the distinct features of pulmonary immunity in selection of CTL escape variants. The likelihood of emergence and the biological impact of CTL escape variants on the clinical outcome of influenza pneumonia in an immunocompetent host, which is relevant for the design of preventive vaccines against this and other respiratory viral infections, are discussed.

Priming of strong, broad, and long-lived HIV type 1 p55gag-specific CD8+ cytotoxic T cells after administration of a virus-like particle vaccine in rhesus macaques

Despite advances in the clinical management of HIV infection, using combinations of antiretroviral pharmaceuticals, a safe and efficacious vaccine is needed to limit the AIDS pandemic. It is now thought that an effective HIV-1 vaccine should prime both cross-neutralizing antibodies and long-lasting cytotoxic CD8+ T lymphocytes (CTLs) recognizing multiple codominant HIV-1 epitopes. To that end, many novel vaccine strategies have been tested. However, only a few of these strategies, beside those relying on live-attenuated viruses, are able to prime strong CTL responses in nonhuman primates and humans. In this study, three rhesus macaques were immunized with HIV-1 p55gag virus-like particles (VLPs) in the absence of adjuvant to assess the potential of such a vaccine to prime CTL responses. After intramuscular injection of p55gag VLP, all three animals mounted CTL responses against HIV-1 p55gag. Notably, these CTLs primed by vaccination recognized naturally processed peptides and were long lived (>8.5 months) both in the peripheral blood and draining lymph node. Furthermore, these CTLs were directed against multiple HIV-1 p55gag epitopes. This indicated that immunization with p55gag VLP primes strong MHC class I-restricted, CD8+ cell-mediated immune responses and suggested that HIV-1 p55gag VLPs should be a reasonable vaccine candidate, when combined with strategies priming cross-neutralizing antibodies.

Cytokine mRNAs in the nasal-associated lymphoid tissue during influenza virus infection and nasal vaccination

Intranasal immunization with a current inactivated influenza vaccine together with an adjuvant (cholera toxin B subunit supplemented with a trace amount of whole toxin, CTB*) was confirmed in BALB/c mice to mimic influenza virus (A/PR/8/34, H1N1) infection with respect to mucosal IgA antibody responses, in which IgA antibody-forming cell responses in the nasal-associated lymphoid tissue (NALT) were involved with a peak around 7 days after infection or vaccination. Next, the expression of various cytokine mRNAs in the NALT was compared in mice either infected with viruses or immunized with CTB*-combined vaccine, to examine Th cell and cytokine regulation of mucosal IgA antibody responses. In infected mice, strong IL-2, weak IL-4, strong IL-6 and strong IFN-gamma mRNA expressions were induced during early days of infection; especially, IFN-gamma mRNA was expressed by both CD4(+) and CD8(+) T cells around 7 days after infection. In mice given CTB*-combined vaccine, weak IL-2, strong IL-4, strong IL-6 and weak IFN-gamma mRNA expressions were induced during early days of vaccination; especially, IL-4 mRNA was expressed by CD4(+) T cells. Thus, IL-6 mRNAs were expressed strongly in both infected and vaccinated mice. The IFN-gamma-rich cytokine mRNA profiles in the infected mice were reflected upon serum IgG2a-rich Ab responses, while the IL-4-rich profiles in the vaccinated mice were reflected upon the IgG1-rich Ab responses. Thus, influenza virus infection and CTB*-combined nasal vaccine induced Th1 dominant and Th2 dominant cytokine profiles, respectively, while the similarity of mucosal IgA antibody responses between infection and vaccination could be explained by the appearance of IL-6 mRNAs.

Protection and antibody responses in different strains of mouse immunized with plasmid DNAs encoding influenza virus haemagglutinin, neuraminidase and nucleoprotein

Protection against influenza virus infection and antibody responses in mice vaccinated with plasmid DNAs encoding haemagglutinin (HA), neuraminidase (NA) and nucleoprotein (NP) were compared among BALB/c (H-2d), B10 (H-2b) and C3H (H-2k) mice. Mice were inoculated with each DNA construct twice, 3 weeks apart, at a dose of 1 microg per mouse by particle-mediated DNA transfer (gene gun) to the epidermis. They were challenged with a lethal dose of the homologous virus 7 days after the second vaccination. NA-DNA provided significant protection in all strains of mouse, whereas HA-DNA afforded significant protection only in BALB/c mice. The serum antibody titres against NA or HA molecules in BALB/c, C3H and B10 mice were high, intermediate and low, respectively. NP-DNA failed to provide protection in any strain of mouse, and elicited low titres of anti-NP antibodies. These results suggest that NA-DNA can be used as a vaccine component to provide effective protection against influenza virus infection in various strains of mouse.

Is there a role for a mucosal influenza vaccine in the elderly?

Influenza infection is an acute respiratory disease with a high morbidity and significant mortality, particularly among the elderly and individuals with chronic diseases. The majority of countries now recommend annual influenza vaccination for all people aged 65 years or older, and for those with high risk conditions. Most commercially available influenza vaccines are administered systemically and while these are effective in children and young adults, efficacy levels in elderly individuals have been reported to be much lower. Mucosal vaccines may offer an improved vaccine strategy for protection of the elderly. As the influenza virus causes a respiratory infection, it is potentially more beneficial to administer a vaccine that will boost protection in the mucosal surfaces of the upper and lower respiratory tract. Mucosal influenza vaccines are aimed at stimulating protective immunity in the respiratory tract via oral or intranasal immunisation. This review examines our present knowledge of mucosal immunity and current strategies for mucosal vaccination. It also stresses that the use of serum antibody levels as a 'surrogate marker' for protection against influenza is potentially misleading; serum antibody, for example, may be a quite inappropriate marker to assess a mucosal vaccine. This marker does not reflect other immune responses to vaccination that are crucial for protection.

Antibody responses to DNA vaccination of horses using the influenza virus hemagglutinin gene

Equine influenza virus infection remains one of the most important infectious diseases of the horse, yet current vaccines offer only limited protection. The equine immune response to natural influenza virus infection results in long-term protective immunity, and is characterized by mucosal IgA and serum IgGa and IgGb antibody responses. DNA vaccination offers a radical alternative to conventional vaccines, with the potential to generate the same protective immune responses seen following viral infection. Antigen-specific antibody isotype responses in serum and mucosal secretions were studied in ponies following particle-mediated delivery of hemagglutinin (HA)-DNA vaccination on three occasions at approximately 63-day intervals. One group of four ponies were vaccinated at skin and mucosal sites and the another group were vaccinated at skin sites only. All ponies were subjected to a challenge infection 30 days after the third vaccination. Skin and mucosal vaccination provided complete protection from clinical signs of infection, while skin vaccination provided partial protection; DNA vaccination provided partial protection from viral shedding. DNA vaccination generated only IgGa and IgGb antibody responses, which occurred with a higher frequency in the skin and mucosa vaccinated ponies. No mucosal IgA response was generated prior to challenge infection and IgA responses were only detected in those ponies which shed virus postchallenge. These results demonstrate that HA-DNA vaccination induces IgG(a) and IgG(b) antibody responses which are associated with protection in the absence of mucosal IgA responses. In addition, additional DNA vaccinations of mucosal sites increased protection and the frequency of seroconversion in ponies.

Perforin-independent CD8(+) T-cell-mediated cytotoxicity of alveolar epithelial cells is preferentially mediated by tumor necrosis factor-alpha: relative insensitivity to Fas ligand

CD8(+) T cells appear to play an important pathophysiologic role in many inflammatory lung diseases. The primary effector function of this T-cell subset is cytolysis of virus-infected cells, and it is widely believed that there are two primary molecular mechanisms by which this occurs: the perforin/granzyme-mediated pathway of cytolysis, and the Fas ligand (FasL)-Fas (CD95/APO-1) pathway of induction of target-cell apoptosis. This conclusion is based primarily on data obtained with hematopoetic cell lines as target cells. There is also a growing body of evidence that Fas is involved in the transduction of apoptotic signals in a variety of inflammatory disease states, particularly involving the liver and the lung. In the study reported here we took advantage of a novel in vitro assay to directly assess the effector mechanisms employed in CD8(+) T-cell-mediated cytolysis of alveolar epithelial cells. We present evidence that FasL-induced, Fas-mediated apoptosis does not directly contribute to T-cell-mediated cytolysis of alveolar epithelial-derived cells, even though Fas is expressed and functional on these cells. We also demonstrated that the perforin-independent cytolytic activity of CD8(+) T cells against alveolar epithelial-derived cells is explained entirely by tumor necrosis factor-alpha (TNF-alpha), which is expressed on CD8(+) T cells. Furthermore, we show that bystander cytolysis of alveolar epithelial-derived cells by antiviral CD8(+) T cells is entirely perforin-independent. This activity is mediated exclusively by TNF-alpha. Both alveolar epithelial-derived cells and primary murine type II cells show susceptibility to apoptosis triggered by soluble TNF-alpha, without the need for transcriptional or translational inhibition. We also confirmed the resistance of alveolar type II cells to FasL in vivo by performing adoptive transfer of perforin-deficient antiviral CD8(+) T cells into transgenic mice expressing a target antigen in type II epithelial cells. Significant lung injury developed in the transgenic CD8(+) T-cell recipients, whether or not Fas was expressed in these animals. Furthermore, preincubation of the T cells with antibody to TNF-alpha completely abolished the injury. These results suggest that alveolar epithelial cells are relatively sensitive to T cell-triggered, TNF-alpha-mediated apoptosis, and resistant to apoptosis triggered by FasL. These observations may have important ramifications for understanding of the pathophysiology of interstitial and inflammatory lung diseases.

Virus-specific immunity after gene therapy in a murine model of severe combined immunodeficiency

Human severe combined immunodeficiency (SCID) can be caused by defects in Janus kinase 3 (JAK3)-dependent cytokine signaling pathways. As a result, patients are at high risk of life-threatening infection. A JAK3 -/- SCID mouse model for the human disease has been used to test whether transplant with retrovirally transduced bone marrow (BM) cells (JAK3 BMT) could restore immunity to an influenza A virus. The immune responses also were compared directly with those for mice transplanted with wild-type BM (+/+ BMT). After infection, approximately 90% of the JAK3 BMT or +/+ BMT mice survived, whereas all of the JAK3 -/- mice died within 29 days. Normal levels of influenza-specific IgG were present in plasma from JAK3 BMT mice at 14 days after respiratory challenge, indicating restoration of B cell function. Influenza-specific CD4(+) and CD8(+) T cells were detected in the spleen and lymph nodes, and virus-specific CD8(+) effectors localized to the lungs of the JAK3 BMT mice. The kinetics of the specific host response correlated with complete clearance of the virus within 2 weeks of the initial exposure. By contrast, the JAK3 -/- mice did not show any evidence of viral immunity and were unable to control this viral pneumonia. Retroviral-mediated JAK3 gene transfer thus restores diverse aspects of cellular and humoral immunity and has obvious potential for human autologous BMT.

In vivo migration and function of transferred HIV-1-specific cytotoxic T cells

The persistence of HIV replication in infected individuals may reflect an inadequate host HIV-specific CD8+ cytotoxic T lymphocyte (CTL) response. The functional activity of HIV-specific CTLs and the ability of these effector cells to migrate in vivo to sites of infection was directly assessed by expanding autologous HIV-1 Gag-specific CD8+ CTL clones in vitro and adoptively transferring these CTLs to HIV-infected individuals. The transferred CTLs retained lytic function in vivo, accumulated adjacent to HIV-infected cells in lymph nodes and transiently reduced the levels of circulating productively infected CD4+ T cells. These results provide direct evidence that HIV-specific CTLs target sites of HIV replication and mediate antiviral activity, and indicate that the development of immunotherapeutic approaches to sustain a strong CTL response to HIV may be a useful adjunct to treatment of HIV infection.

Immunopotentiation of humoral and cellular responses to inactivated influenza vaccines by two different adjuvants with potential for human use

Two quite different adjuvants, currently under development for use in humans, have been examined for their effects on the magnitude and type of immunity elicited in response to inactivated influenza vaccine. Immunostimulating complexes (ISCOM adjuvant) contain the saponin ISCOPREP 703, and SPT is an oil-in-water emulsion of squalane, non-ionic block copolymer (L121) and Tween 80. Influenza virus vaccines formulated in either adjuvant were far superior to the non-adjuvanted aqueous vaccine in eliciting antibody and T-cell responses in mice, particularly at lower doses of antigen. In addition, the vaccines containing adjuvant were superior in eliciting protective immunity. One of the shortcomings of the unadjuvanted inactivated influenza vaccine was its inability to elicit a primary proliferative T-cell response. However, after one dose of either adjuvanted vaccine, strong proliferative responses were achieved. We also show that subcutaneous vaccination with inactivated vaccines is capable of modulating the isotype profile of antibody secreting cells generated in the lungs of mice in response to intranasal challenge with live virus. In this system, the isotype of antibody elicited after challenge of mice that had received ISCOM vaccine more closely mimicked that of animals vaccinated with live virus.

Structural and functional consequences of alveolar cell recognition by CD8(+) T lymphocytes in experimental lung disease

CD8(+) T cells infiltrate the lung in many clinical conditions, particularly in interstitial lung disease. The role(s) that CD8(+) T cells might be playing in the pathogenesis of inflammatory lung disease is unclear at present, as is the direct contribution of CD8(+) T cell effector activities to lung injury. This report describes a transgenic model used to evaluate the impact, on respiratory structure and function, of CD8(+) T lymphocyte recognition of a target antigen expressed endogenously in alveolar epithelial cells. We found that adoptive transfer of cloned CD8(+) cytotoxic T lymphocytes (CTLs) specific for an alveolar neo-antigen (influenza hemagglutinin) leads to progressive lethal injury in transgenic mice, which dramatically affects lung structure and function. Transgenic recipients of CD8(+) CTLs exhibited tachypnea and progressive weight loss, becoming moribund over a period of several days. Concomitantly, the animals developed a progressive interstitial pneumonitis characterized initially by lymphocytic infiltration of alveolar walls and spaces, followed by an exuberant mononuclear cell infiltration that correlated with restrictive pulmonary mechanics and a progressive diffusion impairment. These results indicate that antigen-specific CD8(+) T cell recognition of an alveolar epithelial "autoantigen" is, in and of itself, sufficient to trigger an inflammatory cascade that results in the histological and physiological manifestations of interstitial pneumonia.

Contribution of virus-specific CD8+ cytotoxic T cells to virus clearance or pathologic manifestations of influenza virus infection in a T cell receptor transgenic mouse model

The ability of influenza virus to evade immune surveillance by neutralizing antibodies (Abs) directed against its variable surface antigens provides a challenge to the development of effective vaccines. CD8+ cytotoxic T lymphocytes (CTLs) restricted by class I major histocompatibility complex molecules are important in establishing immunity to influenza virus because they recognize internal viral proteins which are conserved between multiple viral strains. In contrast, protective Abs are strain-specific. However, the precise role of effector CD8+ CTLs in protection from influenza virus infection, critical for understanding disease pathogenesis, has not been well defined. In transgenic mice with a very high frequency of antiinfluenza CTL precursors, but without protective Abs, CD8+ CTLs conferred protection against low dose viral challenge, but exacerbated viral pathology and caused mortality at high viral dose. The data suggest a dual role for CD8+ CTLs against influenza, which may present a challenge to the development of effective CTL vaccines. Effector mechanisms used by CD8+ CTLs in orchestrating clearance of virus and recovery from experimental influenza infection, or potentiation of lethal pathology, are discussed.

Characterization of the cytolytic T-lymphocyte response to a candidate vaccine strain of equine herpesvirus 1 in CBA mice

The cytolytic T-lymphocyte (CTL) response to respiratory infection with equine herpesvirus 1 (EHV-1) in CBA (H-2(k)) mice was investigated. Intranasal (i.n.) inoculation of mice with the attenuated EHV-1 strain KyA resulted in the generation of a primary virus-specific CTL response in the draining mediastinal lymph nodes 5 days following infection. EHV-1-specific CTL could be restimulated from the spleen up to 26 weeks after the resolution of infection, indicating that a long-lived memory CTL population was generated. Depletion of CD8+ T cells by treatment with antibody and complement prior to assay eliminated CTL activity from both primary and memory populations, indicating that cytolytic activity in this model was mediated by class I major histocompatibility complex-restricted, CD8+ T cells. A single i.n. inoculation with KyA induced protective immunity against infection with the pathogenic EHV-1 strain, RacL11. The adoptive transfer of splenocytes from KyA-immune donors into sublethally irradiated recipients resulted in a greater than 250-fold reduction in RacL11 in the lung. The elimination of both CD4+ and CD8+ T cells from the transferred cells abrogated clearance of RacL11, while the selective depletion of either subpopulation alone had little effect. These results suggested that both lymphocyte subpopulations contribute to viral clearance, with either subpopulation alone being sufficient.

Role of interleukin-12 in primary influenza virus infection

The effect of endogenous interleukin-12 (IL-12) on the influenza virus immune response in BALB/c mice was evaluated. Following primary influenza virus infection, IL-12 mRNA and protein are detected in the lung, with live virus being required for cytokine induction. Endogenous IL-12 contributes to early NK cell-dependent gamma interferon (IFN-gamma) production (days 3 and 5) but not late T-cell-dependent IFN-gamma secretion (day 7). IL-12 contributes to the inhibition of early virus replication but is not required for virus clearance. IL-12 also modestly contributes to the activation of cytotoxic T lymphocytes. Thus, in this model of experimental influenza virus infection, endogenous IL-12 contributes primarily to the early development and activation of the innate immune response.

Induction of CD8+ T Cell Responses to Dominant and Subdominant Epitopes and Protective Immunity to Sendai Virus Infection by DNA Vaccination

While recent studies have demonstrated that DNA vaccination induces potent CD8+ T cell memory in vivo, it is unclear whether this memory is qualitatively and quantitatively comparable with that induced by natural viral infection. In the current studies, we have investigated the induction of CD8+ memory CTL responses to Sendai virus nucleoprotein (NP) in C57BL/6 mice following gene gun vaccination. The data demonstrate that this mode of vaccination induces potent long-lived memory CTL precursors (CTLp) specific for both the dominant (NP324–332/Kb) and the subdominant (NP324–332/Db) epitopes of NP. The frequencies of T cells specific for each of these epitopes in the spleen is about 1:2000 CD8+ T cells, similar to those induced by intranasal infection with Sendai virus. Moreover, the induction of memory CTLp by DNA vaccination is independent of MHC class II molecules or Ab, as is the case for memory CTLp induction by live Sendai virus infection. CTLp specific for both epitopes are capable of migrating to the lung following Sendai virus infection and express potent cytotoxic activity at the site of infection. Consistent with this activity, DNA vaccination with Sendai virus NP induced a substantial degree of Ab-independent protection from a challenge with a lethal dose of Sendai virus. Taken together, these data demonstrate that for the parameters tested, DNA vaccination is indistinguishable from live virus infection in terms of priming functional memory CTLp with broad specificity for both dominant and subdominant T cell epitopes.

Activation of influenza-specific memory cytotoxic T lymphocytes by Concanavalin A stimulation

Traditionally, the in vitro activation of virus-specific memory cytotoxic T lymphocytes (CTLs) has been achieved by stimulating the CTLs with antigen-presenting cells (APCs) infected with an appropriate virus or pulsed with virus-specific antigenic peptides. Here, we describe the utilization of the polyclonal activator Concanavalin A (ConA) for in vitro restimulation of memory CTLs from virus-primed mice. Using this simple method, the activation of splenocytes with ConA for 3 days (i) eliminates the need to stimulate with virus-pulsed APCs and (ii) generates CD8+ CTLs that exhibit virus specificity and MHC-restricted lytic activity similar to CTLs obtained by conventional viral restimulation. In vitro ConA stimulation of splenocytes from BALB/c mice primed with the A/Texas/77 or A/Japanese/57 strain of influenza virus and from C57L/J mice infected with the A/Texas strain, generated CTLs with specific lytic activity. Hence reactivation of memory CTLs by this method is a general phenomenon rather than a mouse or viral strain-specific one. The ConA stimulation method used here had a recall of long-term (1 year) memory CTLs that effectively lysed virally infected targets. Further ConA-stimulated effector lymphocytes from virally primed animals have been shown to recognize and subsequently lyse target cells pulsed with virus or virus-derived peptides. The ConA reactivation of specific anti-viral CTLs may facilitate (i) studying anti-viral CTL responses and (ii) identifying of viral epitopes when unknown or when appropriate viral stimulation is impossible.

Comparison of neutralizing and hemagglutination-inhibiting antibody responses to influenza A virus vaccination of human immunodeficiency virus-infected individuals

A neutralization enzyme immunoassay (N-EIA) was used to determine the neutralizing serum antibody titers to influenza A/Taiwan/1/86 (H1N1) and Beijing/353/89 (H3N2) viruses after vaccination of 51 human immunodeficiency virus (HIV) type 1-infected individuals and 10 healthy noninfected controls against influenza virus infection. Overall, the N-EIA titers correlated well with the hemagglutination-inhibition (HAI) titers that were observed in the same samples in a previous study (F. P. Kroon, J. T. van Dissel, J. C. de Jong, and R. van Furth, AIDS 8:469-476,1994). The N-EIA appeared to be more sensitive than the HAI test. Significantly more fourfold or higher rises in N-EIA titer and higher mean N-EIA titers occurred in HIV-infected individuals with > or =200 CD4+ cells per microl than in those with <200 CD4+ cells per microl.

Mechanism of Protective Immunity Against Influenza Virus Infection in Mice Without Antibodies

There is considerable interest in developing viral vaccines intended to induce T cell immunity, especially cytotoxic CD8+ T lymphocytes, when Abs are not protective or are too narrow in viral strain specificity. We have studied protective immunity in doubly inactivated (DI) mice devoid of Abs and mature B cells. When infected with influenza B virus, these mice cleared the virus in a process dependent upon CD8+ T lymphocytes. Cytotoxic activity was detected in lung lymphocytes of DI mice after primary or secondary infection, and was abrogated by depletion of CD8+ cells in vivo. Challenge experiments showed that DI mice could be protected by immunization against reinfection 1 mo later, and protection was virus specific. Depletion of CD4+ or CD8+ T cells in vivo during the challenge period partially abrogated, and depletion of both subsets completely abrogated, the protection. This indicates that both CD4+ and CD8+ T cells are required effectors in the optimal control of virus replication. Thus, when Abs fail to protect against varying challenge viruses, as is the case with variant strains of influenza and HIV, there is hope that T cells might be able to act alone.

Resistance to and recovery from lethal influenza virus infection in B lymphocyte-deficient mice

In the adaptive immune response to most viruses, both the cellular and humoral arms of the immune system play complementary roles in eliminating virus and virus-infected cells and in promoting recovery. To evaluate the relative contribution of CD4+ and CD8+ effector T lymphocytes in virus clearance and recovery, we have examined the host response to lethal type A influenza virus infection in B lymphocyte-deficient mice with a targeted disruption in the immunoglobulin mu heavy chain. Our results indicate that naive B cell-deficient mice have a 50- 100-fold greater susceptibility to lethal type A influenza virus infection than do wild type mice. However, after priming with sublethal doses of influenza, immune B cell-deficient animals show an enhanced resistance to lethal virus infection. This finding indicates that an antibody-independent immune-mediated antiviral mechanism accounts for the increased resistance to lethal virus challenge. To assess the contribution of influenza-specific CD4+ and CD8+ effector T cells in this process, defined clonal populations of influenza-specific CD4+ and CD8+ effector T cells were adoptively transferred into lethally infected B cell-deficient mice. Cloned CD8+ effectors efficiently promoted recovery from lethal infection, whereas cloned CD4+ T cells conferred only partial protection. These results suggest that memory T lymphocytes can act independently of a humoral immune response in order to confer resistance to influenza infection in immune individuals. The potential implications of these results for vaccination against human influenza infection are discussed.

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

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

Influenza vaccination in the elderly

Influenza vaccination of elderly people has been shown to be useful. All vaccine types are well tolerated by higher age group vaccinees. Actually, whole virus vaccine, split virus vaccine and subunit vaccine are used in the vaccination of the elderly. Some studies have suggested that the induction of serum influenza antibody production was reduced in elderly persons when compared with that elicited in younger persons. However, investigations on the protective efficacy of influenza vaccination in the elderly have demonstrated a clinical protection of > or = 50% for preventing hospitalization. Live attenuated influenza vaccine conferred protection similar to that obtained with a conventional subunit vaccine. A virosomal unilamellar trivalent hemagglutinin vaccine showed promising serological results compared with those obtained with a whole cell vaccine and with a subunit vaccine, respectively. The actual policy is to vaccinate persons > or = 65 years of age and the groups that can transmit influenza to them. Each year's vaccine should contain three virus strains representing the influenza viruses that are likely to circulate in the upcoming winter.

Effector CD4+ and CD8+ T-cell mechanisms in the control of respiratory virus infections

The rules for T-cell-mediated control of viruses that infect via the respiratory mucosae show both common themes and differences, depending on the nature of the pathogen. Virus-specific CD8+ cytotoxic T lymphocytes (CTLs) are the key effectors of virus clearance in mice infected with both negative strand RNA viruses (influenza and Sendai) and a DNA virus, the murine gamma-herpesvirus-68 (MHV-68). Recently completed experiments establish that these activated CD8+ T cells indeed operate primarily via contact-dependent lysis. Perforin-mediated cytotoxicity seems to be the preferred mode, though a Fas-based mechanism can apparently serve as an alternative mechanism. Immune CD4+ T cells functioning in the absence of the CD8+ subset cannot eliminate MHV-68 from lung epithelial cells, are somewhat less efficient than the CD8+ CTLs at clearing the RNA viruses, and are generally ineffectual in mice that lack B lymphocytes. Though cytokine secretion by CD4+ and CD8+ T cells in the virus-infected lung may promote both T-cell extravasation and macrophage activation, such processes are not alone sufficient to deal consistently with any of these infections. However, CD4+ T help is mandatory for an effective B-cell response, and can operate to promote the clonal expansion of virus-specific CD8+ T cells in the lymph nodes and spleen. Furthermore, a concurrent CD4+ T-cell response seems to be essential for maintaining continued CD8+ T-cell surveillance and effector capacity through the persistent, latent phase of MHV-68 infection in B cells. Thus, the evidence to date supports a very traditional view; CD8+ T cells function mainly as killers and the CD4+ T cells as helpers in these respiratory virus infections.

Role of the B-cell response in recovery of mice from primary influenza virus infection

Recovery from influenza virus infection has long been known to require an intact T-cell compartment. More recent studies revealed that CD8 and CD4 T cells can promote recovery through independent mechanisms. The CD4 T-cell-dependent recovery process appears to operate primarily through promotion of the T-dependent antibody response as B-cell-deficient microMT mice cannot recover from infection if they have been depleted of CD8 T cells. The potential therapeutic activity of the B-cell response was further studied by transfer of antibodies into infected SCID mice. At the dose of 200 micrograms/mouse, most antibodies (of IgG2a isotype) to the viral transmembrane protein HA cured the infection, while those to the transmembrane proteins NA and M2 suppressed virus titers in the lung but failed to clear the infection. The ability of passive antibody to resolve the infection was closely related to its prophylactic activity, suggesting that neutralization of progeny virus (VN) played an important role in the process of virus clearance in vivo, while reaction of antibodies with infected host cells contributed to but was insufficient, on its own, for cure. HA-specific antibodies of IgM and IgA isotypes were therapeutically ineffective against pulmonary infection, presumably because of a preferential delivery into the upper respiratory tract, while IgG exhibited highest activity against pulmonary and minimal activity against nasal infection. B cells appear to be of similar importance for recovery from primary infection as CD8 T cells.

Influenza virus neutralizing antibodies and IgG isotype profiles after immunization of mice with influenza A subunit vaccine using various adjuvants

The influence of various adjuvants on the development of influenza virus neutralizing antibodies and distribution of anti-influenza virus IgG isotypes after immunization of mice with influenza A (H3N2) subunit vaccine was investigated. Serum titres of influenza virus neutralizing antibodies and titres of influenza specific IgG isotypes were determined by a neutralization enzyme immunoassay (N-EIA) and a cell-associated antigen enzyme immunoassay (CA-EIA), respectively. Serum antibody titres as measured by the two tests correlated highly (r = 0.82; P < 0.001). N-EIA titres were enhanced by 38- and 34-fold, when L180.5/RaLPS and FCA, respectively, were administered with 1 microgram of vaccine. The adjuvants Q-VAC, L180.5 [W/O/W], L180.5 alone and Montanide ISA 740 were only moderately or not effective in enhancing the immune response to the 1 microgram dose of vaccine. The Q-VAC and L180.5/RaLPS adjuvants favoured IgG2a and IgG2b isotype responses to influenza compared to the other adjuvants. We suggest that N-EIA and CA-EIA may be valuable tools to monitor the effects of adjuvants on the neutralizing antibody and antibody isotype responses after influenza vaccination.

Surfactant protein A, but not surfactant protein D, is an opsonin for influenza A virus phagocytosis by rat alveolar macrophages

Surfactant protein A (SP-A) and surfactant protein D (SP-D) are collectins, and both proteins were shown to interact with influenza A virus and alveolar macrophages. However, it is not known whether SP-A and SP-D can serve as opsonins for the phagocytosis of influenza A virus by alveolar macrophages. In the present study, we investigated the opsonic activities of SP-A and SP-D for phagocytosis of fluorescein isothiocyanate (FITC)-labeled influenza A (H3N2) virus by rat alveolar macrophages using flow cytometry. SP-A enhanced the association of the virus with macrophages in a dose-dependent manner, reaching a maximum at an SP-A concentration of 60 microg/ml. An approximate threefold increase in association of influenza A virus with alveolar macrophages in the presence of SP-A over control incubations which contained no SP-A was observed. Half of the total cell-associated fluorescence could be quenched as demonstrated using the extracellular quenching dye trypan blue. These results indicate that SP-A mediates internalization of FITC-labeled influenza A (H3N2) virus by alveolar macrophages. Removal of the carbohydrate moiety of SP-A by N-glycosidase F treatment or cleavage of its sialic acid residues by neuraminidase abolished the enhancement of the phagocytosis of FITC-labeled influenza A virus by alveolar macrophages. Mannan, a mannose homopolysaccharide known to bind to the carbohydrate-binding domain of SP-A, did not affect the SP-A-mediated phagocytosis of FITC-labeled influenza by alveolar macrophages. In contrast, SP-D neither enhanced the association of FITC-labeled influenza A virus with alveolar macrophages nor affected the opsonic activity of SP-A for FITC-labeled influenza A (H3N2) virus at the SP-D concentrations tested. It is concluded that SP-A acts via its sialic acid residues as an opsonin in the phagocytosis of influenza A virus by alveolar macrophages.

Protective responses in mice to vaccination with multiply administered cold-adapted influenza vaccine reassortants and wild-type viruses

Protective responses to influenza vaccine reassortants derived from the cold-adapted (ca) donor strains A/Leningrad/134/17/57 and B/USSR/60/69 and wild-type epidemic viruses were studied in two strains of mice. Preliminary experiments revealed that, when mixtures of three viruses were inoculated intranasally to mice with 50 microliters containing 10(6) EID50 per 200 microliters (10(5.4) EID50 per mouse), interference between strains did not occur. However, interference with the growth of the influenza reassortant B/60/32/R took place if its concentration in the mixture was reduced to 10(5) (10(4.4) per mouse) or if it was inoculated at 10(6) EID50 (10(5.4) per mouse) in the presence of the influenza reassortant R/34 and two other influenza A epidemic strains; interference was unrelated to serological responses to infection with B/60/32/R. Despite evidence of interference, mice inoculated with the same mixtures in two identical doses, three weeks apart, were able to clear a challenge from each of seven homotypic and heterotypic influenza A and B strains. Heterotypic clearance of influenza A challenge viruses was greater following mixed infection, indicating that common determinants within the surface antigen glycoproteins contributed to immune responses which were broader than could be expected to be induced by parenteral vaccination.

Influenza-specific immunity induced by recombinant Listeria monocytogenes vaccines

In this study, we evaluate two Listeria monocytogenes strains that express influenza nucleoprotein (NP) sequences for their ability to protect against challenge with influenza-virus. The construction of one strain, which expresses only the Kd restricted NP epitope (NP 147-155), is described in this study; the other strain, which expresses the full NP sequence in the form of a fusion protein, has been described previously. The ability of the two strains to present the Kd restricted NP epitope in vitro and induce NP-specific CTL in vivo is also described. Mice immunized by the intravenous route with either strain cleared a subsequent (3 weeks post-immunization) influenza virus infection more rapidly as indicated by reduced virus titers in the lungs 5 days after challenge. Efficacy of both recombinant L. monocytogenes strains as vaccines in this system was equivalent and equal to that of recombinant vaccinia expressing NP.

The immunosenescent phenotype in mice and humans can be defined by alterations in the natural immunity reversal by immunomodulation with oral AM3

The reactivities of monocyte/macrophages and natural killer (NK) cells (natural immunity) were evaluated following the administration of the biological response modifier AM3. The lower number of macrophages and NK cells in middle-aged mice (MAM) compared to young adult mice (YAM) were significantly elevated following AM3 treatment to equal or greater than YAM values. Both macrophage and NK cell cytotoxicity peaked at two days following AM3 treatment and remained elevated over control values for up to 8 days following a four days treatment regimen by the oral route. Of particular interest was the clinical effect of AM3 treatment in chronic bronchitis (CB) patients and various aged volunteers. In middle-aged patients with chronic bronchitis (MACBpts) AM3 treatment resulted in significant increases in the number of monocytes as well as their phagocytic and chemotactic activity. Differential NK cell cytotoxicities were observed in MACBpts compared to middle-aged healthy adults (MAHA) and young healthy adults (YHA). Cytotoxicity in YHA was 2-fold higher than MAHA and 5-fold higher than MACBpts. The depressed number of NK cells in MACBpts was reversed following the AM3 treatment to near NK cell levels in YHA. These observations help to explain how AM3 aids in the restoration of natural cellular immunity and its possible application as an adjuvant to bacterial & viral vaccines as well as in the treatment CB.

Summary of a clinical trial with liposome-adjuvanted influenza A virus vaccine in elderly adults

In a randomized, double-blinded study, 77 elderly seropositive volunteers were immunized with either liposome-adjuvanted or control subvirion vaccine containing 15 micrograms/dose of haemagglutinin from influenza A/Taiwan/1/86 (H1N1) virus. The liposome vaccine was well-tolerated but elicited serologic responses that were no different in frequency or magnitude from those induced by the control vaccine. Less than 20% of subjects in either group mounted a 4-fold or greater rise in antibody titer. Peripheral blood anti-influenza A cytotoxic T lymphocyte activity was enhanced to a greater extent by the liposome vaccine than by the control subvirion vaccine. It remains unclear whether liposome-adjuvanted formulations would have an advantage over conventional influenza vaccines for routine annual reimmunization of targeted high-risk populations.

Distinct costimulatory molecules are required for the induction of effector and memory cytotoxic T lymphocytes

A successful T cell immune response has two major products: effector T cells which directly or indirectly remove the antigens, and memory T cells, which allow a faster and more efficient recall response when challenged by related antigens. An important issue is whether costimulatory molecules on the antigen-presenting cells are involved in determining whether T cells will differentiate into effector or memory cells after antigenic stimulation. To address this issue, we have produced mice with targeted mutations of either the heat-stable antigen (HSA), or both HSA and CD28. We show that CD28/B7 and HSA provide two alternative costimulatory pathways for induction of immunological memory to influenza virus. Furthermore, our results revealed that B7 is essential for the generation of effector T cells from either naive or memory T cells, while HSA is not necessary for the generation of effector T cells. Our results demonstrate that the induction of memory T cells and effector T cells can utilize distinct costimulatory molecules. These results have important implications on lineage relationship between effector and memory T cells.

Possible correlation between low antigenic drift of A(H1N1) influenza viruses and induction of HI antibodies

This study examined whether, during a seven-year period of low A(H1N1) influenza virus antigenic drift (1988-1989 and 1994-1995, winters), humoral antibody response of elderly volunteers to influenza vaccines could suggest a lack of antibody pressure for drift. In all the years studied A/Taiwan/1/86, the A(H1N1) vaccine component, had a low ability to induce protective hemagglutination-inhibiting (HI) antibody titres (> or = 1:40). However a similar low immunogenicity was found for some of the different A(H3N2) strain variants of influenza virus, co-circulating in the same period and showing a regular extent of antigenic variations. Although our data could be at least in part explained by the type of study population (elderly and repeatedly vaccinated), postepidemic serological studies did not evidence a consistently lower ability in mounting protective immune response in elderly people as compared with younger against the influenza strains studied. Therefore, our present results did not exclude a true low immunogenicity of A/Taiwan and of some A(H3N2) influenza strains, circulating in the winters examined. This suggests that, besides the necessity to evade prior immunity, additional factors could influence the frequency of influenza viruses antigenic drifts.

Role of different lymphoid tissues in the initiation and maintenance of DNA-raised antibody responses to the influenza virus H1 glycoprotein

Antibody responses in mice immunized by a single gene gun inoculation of plasmid expressing the influenza virus H1 hemagglutinin and in mice immunized by a sublethal H1 influenza virus infection have been compared. Both immunizations raised long-lived serum responses that were associated with the localization of antibody-secreting cells (ASC) to the bone marrow. However, the kinetics of these responses were 4 to 8 weeks slower in the DNA-immunized than in the infection-primed mice. Following a gene gun booster, the presence of ASC in the inguinal lymph nodes, but not in other lymph nodes, revealed gene gun responses being initiated in the nodes that drain the skin target site. Both pre- and postchallenge, the DNA-immunized mice had 5- to 10-times-lower levels of antibody and ASC than the infection-primed mice.

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.

Functionally distinct T cells in three compartments of the respiratory tract after influenza virus infection

This study aimed to resolve, firstly, whether T cell responses induced in one tissue site are similar to those induced by the same antigen in another site and, secondly, whether influenza virus infection induces one predominant type of T cell response locally in the respiratory tract. To address these questions, T cell responses in three compartments of the respiratory tract were compared after infection of mice with a sublethal dose of influenza virus: the draining mediastinal lymph nodes (MLN), the lung parenchyma and the airways. Each compartment harbored a T cell response substantially different from that found at the other sites. A preferential accumulation of ex vivo-cytolytic CD8+ T cells was found in the airways (CD4/CD8 ratio 1:2) and to a lesser extent in the lung parenchyma (CD4/CD8 ratio 1:1). T cells from both compartments expressed high levels of various cytokine mRNA, but showed differences in their respective expression pattern, with those from lung tissue showing particularly high levels of IFN-gamma mRNA. The response in the draining lymph nodes, on the other hand, was dominated by CD4+ T cells (CD4/CD8 ratio 2:1) with a higher proliferative capacity (after TCR/CD3 cross-linking) and which provided better B cell help in vitro than CD4+ T cells isolated from lung tissue. T cells from MLN expressed mRNA for a variety of cytokines with only low levels of IFN-gamma mRNA and they showed no CTL activity ex vivo. These functional differences were not due to differences in the kinetics of the response, or to the higher frequencies of activated T cells in lung tissue and airways compared to MLN, since the differences remained when cell-sorter-purified activated (CD18hi, CD44hi) T cells from MLN and lung tissue were compared in a time-course study. Taken together, these findings indicate that pathogens such as influenza virus induce a heterogenous set of T cell responses in different tissue sites affected by the infection.

A lung-specific neo-antigen elicits specific CD8+ T cell tolerance with preserved CD4+ T cell reactivity. Implications for immune-mediated lung disease

The A/Japan/57 influenza hemagglutinin (HA) was expressed in BALB/c mice under the transcriptional control of the surfactant protein C (SP-C) promoter, resulting in expression of HA in type II alveolar epithelial cells, as well as low level variable expression in other tissues, including the thymus in some of the founder lines. Transgenic animals were able to recover from infection with A/Japan/57 influenza, and they were able to mount antibody responses to A/Japan/57 HA in titers similar to wild type. We therefore tested their CD4+ T lymphocyte responses to HA and found them to be similar to wild type responses. However, CD8+ T cells from A/Japan/57-infected transgenic animals were unable to express cytolytic activity against target cells expressing the A/Japan/57 HA. The CD8+ T cell tolerance was also extremely specific, since transgenics immunized with an influenza strain containing a single amino acid substitution in a dominant HA epitope were able to mount full cytolytic responses to that epitope, but not the wild-type epitope. Adoptive transfer of CD8+ T cell clones into transgenic animals resulted extensive interstitial pneumonitis that was antigen-specific and associated with significant morbidity and mortality. We conclude that a lung-specific transgene may lead to specific CD8+ T cell tolerance, with CD4+ T cell and B cell reactivity to the antigen, and that CD4+ T cell reactivity may remain intact to an antigen expressed in the thymus, even when CD8+ T cell tolerance exists. This observation may have profound implications concerning immune-mediated lung diseases, particularly those mediated by CD4+ T cells.

Cellular mechanisms involved in protection and recovery from influenza virus infection in immunodeficient mice

We investigated the role of different lymphocyte subpopulations in the host defense reaction against influenza virus infection, taking advantage of various immunodeficient mouse strains. Whereas, following immunization, wild-type animals showed complete protection against challenge with a lethal dose of A/PR8/34 (PR8) virus, mice that lack both B and T cells but not NK cells (namely, scid and RAG2(-/-) mice) did not display any protective effect in similar conditions. By contrast, J(H)D(-/-) mice devoid of B cells and immunized with virus showed a protective response after challenge with a lethal dose. The immunized J(H)D(-/-) mice that survived completely recovered from the influenza virus infection. Immunized J(H)D(-/+) mice exhibited a more complete protection, suggesting the role of specific antibodies in resistance to infection. To assess the role of natural immunity in the host defense against influenza virus, we carried out experiments with scid mice challenged with lower but still lethal doses of PR8 virus. While an increased NK activity and an increased number of NK1.1+ cells in lungs of scid mice infected with PR8 virus were noted, in vivo depletion of the NK1.1+ cells did not affect the overall survival of the mice. Our results show that specific T cells mediate protection and recovery of J(H)D(-/-) mice immunized with live virus and challenged with lethal doses of influenza virus.

Do cytotoxic T lymphocytes clear some HIV/SIV infections?

Early work on the roles of cytotoxic T lymphocytes (CTLs) in acute viral infections in animal models showed that i) the clearance of virus coincided with the increase in CTL activity rather than specific antibody levels, ii) transfer of CTLs after infection could protect from a lethal dose of virus, and iii) in primed, compared to naive, animals, CTL activity appeared 1-3 days earlier after a challenge infection. There is now a series of findings with individuals who have been exposed to HIV but are HIV-seronegative that suggest a protective role for CTLs. Usually after in vitro culture, HIV-specific CTLs have been isolated from i) infants born of infected mothers, ii) long-time partners of HIV-infected people, iii) some prostitutes in Africa, and iv). Most recently, 7/20 seronegative health care workers exposed once to HIV have been shown to possess HIV env-specific CTLs. The findings suggest that CTLs (a type I T cell response) may rapidly clear a low dose of HIV. Experiments with SIV are proposed that may provide more direct supporting data for this possibility.

Efficacy of combination therapy with amantadine, thymosin alpha 1 and alpha/beta interferon in mice infected with influenza A virus

The aim of this study was to examine the effects of the antiviral drug amantadine (AMN) administered in combination with thymosin alpha 1 (T alpha 1) and murine alpha/beta interferon (IFN) on mice infected with influenza A PR8 virus. Combined treatment with AMN and T alpha 1, for 4 days, followed by a single injection of IFN, was initiated 1 h after intranasal viral inoculation. The effectiveness of this new chemoimmunotherapy protocol was seen in the long-term survival of a high percentage of animals and was statistically significant when compared to treatment with single agents in conjunction with chemotherapy or to chemotherapy alone. In addition, chemoimmunotherapy treatment reduces the viral titre in the lungs as well as restoring the immunological parameters tested (natural killer cell activity; cytotoxic T-lymphocyte responses; CD4+/CD8+ lymphocyte subsets) with respect to all other groups. These results suggest the potential use of these immunomodulating agents in combination with an antiviral drug in controlling PR8 influenza virus infection.

Superstimulatory influenza virus and highly organized BCR-ligands act synergistically on B cell activation

The influenza virus glycoprotein hemagglutinin (HA) behaves as a superstimulatory protein for B lymphocytes from various species. Polyclonal B cell stimulation mediated by HA can be blocked by soluble anti-Ig antibodies. We here report that, if presented in a highly organized form, i.e., as anti-Ig mAb coupled to dextran (anti-Ig-Dex), conventional BCR-ligands and influenza viruses act synergistically on murine B cell activation. Proliferative responses of both spellen-derived and peritoneal B cells mediated by suboptimal amounts of HA were significantly augmented by costimulation with anti-Ig-Dex, and vice versa. Similarly, anti-Ig-Dex, which on its own cannot induce Ig production in the absence of added cytokines, significantly enhanced Ig synthesis in response to superstimulatory HA. By contrast, poorly organized BCR-ligands (i.e. the same anti-Ig mAb in a soluble form) had either no, or a strong inhibitory effect on virus-triggered lymphocyte activation. Assays with various second messenger-antagonists, however, revealed clear differences in the signaling pathway employed by anti-Ig-Dex and HA, suggesting that the functional synergy between the two multimeric agents is mediated by engagement of distinct transducing elements. Taken together, these results indicate that the superstimulatory function of influenza virus HA represents a molecular strategy to mimick B cell activation by conventional, highly organized particulate-antigens.

Immunoglobulin deficient mice generated by gene targeting as models for studying the immune response

B cell deficient animals obtained by various strategies of gene targeting were used to study the B cell development and examine the role of different immune compartments in the immune response to microbes. Study of muMT, JHD, lambda 5T and JHT models of B cell deficiency, was essential in order to understand the role of pre-B cell receptor in B cell development, allelic exclusion and variable gene rearrangement regulation. In the immune response to influenza virus, a protective role of T cells in a total absence of B cell compartment, was revealed by studying the JHD -/- model. Further, it was established that a T cell compartment is sufficient to mediate the recovery from influenza infection. Examination of immune response in muMT and JHD models of definitive B cell deficiency to various blood stage Plasmodia species, showed that whereas B cells are not required for recovery from infection with P. chabaudi adami, P. vinckei petteri and P. chabaudi chabaudi (CB), B cell compartment is important in the later stages of infection with P. chabaudi chabaudi (AS). Studies carried out in muMT model suggested a possible role for T gamma delta subpopulation in the immune response to blood stage malaria parasite. B cell deficiency models are valuable for understanding the normal and pathological immune response. Studies carried out in muMT model indicated that T cell responses are not significantly affected in the absence of B cells. These data can neither rule out a role for B cells in T cell priming, nor in triggering an effective T cell help for humoral response. Study of double homozygous mice deficient for B cells and FAS or IL-2 gene, pinpointed the role of B cells in pathogenesis of lupus-like nephritis and vasculitis from lpr mouse and in hemolytic anemia from IL-2 -/- mouse model, respectively.

Intranasal immunization of mice against influenza with synthetic peptides anchored to proteosomes

Synthetic vaccines that are based on peptides representing immunogenic epitopes require a carrier molecule as well as an adjuvant in order to be effective. The choice of carriers or adjuvants approved for use in humans is very limited, and a considerable effort is devoted to develop new and efficient delivery systems. One of these vehicles utilizes preparations of outer membranes of meningococci, that form hydrophobic interactions, denoted proteosomes. Immunogenic proteins and peptides can be anchored to these proteosomes vesicles, which may serve as both carrier and adjuvant functions. In the present study we examined the ability of proteosomes to present epitopes of influenza, to elicit specific anti-influenza responses and to protect mice against viral challenge after intranasal immunization. Three influenza peptides were used--one corresponding to amino acid residues 91-108 of the haemagglutinin surface glycoprotein of H3 subtype, which comprises a B-cell epitope, and two from the internal nucleoprotein--a T-helper cell (Th) epitope (residues 55-69) and a cytotoxic T-lymphocyte (CTL) epitope (147-158). Mice were immunized intranasally (i.n.) with preparations containing each of the above epitopes, or various combinations thereof. The results obtained with this system demonstrate that influenza epitopes represented by synthetic peptides anchored to a proteosome carrier elicit both humoral and cellular specific immune responses, that can lead to partial protection of the mice from viral challenge. The importance of immunizing with vaccines containing both B- and T-cell peptide epitopes was emphasized by the demonstration that such vaccines elicited longer lasting immunity and led to more effective protection against influenza viral challenge.

ENV-specific cytotoxic T lymphocyte responses in HIV seronegative health care workers occupationally exposed to HIV-contaminated body fluids

Identification of the components of protective immunity are crucial for the development of effective prophylactic and therapeutic vaccine strategies. Analysis of HIV-specific responses in exposed but uninfected individuals might thus provide a unique resource to elucidate the components and correlates of protective immunity to HIV. In the present study we analyzed HIV-specific cytotoxic and helper T lymphocyte responses in health care workers (HCW) exposed to body fluids from HIV-positive individuals. HCW exposed to blood from HIV-negative individuals as well as healthy donors served as controls. Cytotoxic T lymphocyte (CTL) responses to HIV envelope (env) peptides were detected in 7/20 (35%) HCW exposed to HIV-positive blood and in none of the 20 health care workers exposed to uninfected blood or the seven healthy blood donors studied. HIV-specific CTL responses were detected only after in vitro stimulation, and were MHC class I restricted. No MHC class I restriction elements were uniformly identified among the different responders. 21/28 (75%) HCW exposed to contaminated blood responded to env as measured by IL-2 production to the peptides, in contrast to only 9/38 (24%) HCW exposed to HIV seronegative blood and 3/35 (9%) healthy blood donors. All the HIV exposed individuals were seronegative on repeated ELISA tests, and no evidence of infection was obtained by PCR analysis. These findings indicate that a single exposure to HIV can induce CTL immunity to HIV antigens, in the absence of other evidence of infection.

Direct and indirect control of T-cell activation by keratinocytes

Keratinocytes can function as antigen-presenting cells/accessory cells and regulate T cells with three distinct outcomes, depending on the nature of the stimulus. In the presence of alloantigen, it appears that a "null" event takes place between T cells and keratinocytes, with neither activation nor induction of tolerance. Using nominal antigen, keratinocytes induce antigen-specific tolerance. In contrast, with bacterial-derived superantigens, phytohemagglutinin, or immobilized CD3 monoclonal antibody, keratinocytes can significantly activate resting autologous T-cell proliferation and cytokine release. To understand these highly divergent responses, we focused on the two-signal model of T-cell activation, with particular emphasis on costimulatory molecules expressed by keratinocytes. Such second signals, as highlighted by the B7 and CD28 receptor families, provide useful insights into the complex interactions involving keratinocytes and T cells. In this review, we summarize recent evidence indicating that keratinocytes regulate T-cell activation in a direct and indirect manner by their mutual expression and responsiveness involving adhesion molecules, cytokines, and costimulatory signals. As investigative momentum continues to grow in the fields of immunology and keratinocyte biology, it is likely that manipulation of CD28:B7 interactions will not only provide a useful model to understand further the complexities of skin immune reactions, but will also serve as the basis for new therapeutic opportunities for numerous T-cell-mediated diseases that involve aberrant reactions with keratinocytes.