Virus-specific antibody secreting cell, memory B-cell, and sero-antibody responses in the human influenza challenge model.

BACKGROUND: Antibodies play a major role in the protection against influenza virus in human. However, the antibody level is usually short-lived and the cellular mechanisms underlying influenza virus-specific antibody response to acute infection remain unclear. METHODS: We studied the kinetics and magnitude of influenza virus-specific B-cell and serum antibody responses in relation to virus replication during the course of influenza infection in healthy adult volunteers who were previously seronegative and experimentally infected with seasonal influenza H1N1 A/Brisbane/59/07 virus. RESULTS: Our data demonstrated a robust expansion of the virus-specific antibody-secreting cells (ASCs) and memory B cells in the peripheral blood, which correlated with both the throat viral load and the duration of viral shedding. The ASC response was obviously detected on day 7 post-infection when the virus was completely cleared from nasal samples, and serum hemagglutination-inhibition antibodies were still undetectable. On day 28 postinfection, influenza virus-specific B cells were further identified from the circulating compartment of isotype-switched B cells. CONCLUSIONS: Virus-specific ASCs could be the earliest marker of B-cell response to a new flu virus infection, such as H7N9 in humans.

Perspectives on vaccine development for the elderly.

Modern society is characterized by a steady increase in the aged population. Increasing numbers of elderly people are exposed to infectious diseases in addition to suffering from chronic non-communicable illnesses. Key differences exist between immune responses elicited against infectious agents in the elderly and in the youngest population. Responses in the aged are characterized by a physiological state of impaired immunity. Such state has forced scientist and vaccine manufacturers to re-think the way vaccines are designed and tested in the elderly. Multiple strategies have been used to overcome the consequences of immunosenescence including the use of higher antigen dose, adjuvanted vaccines, and alternative routes of immunization. However, the lack of understanding of the immune regulatory mechanisms underlying immunosenescence in the elderly represents one of the main hurdles in the pathway to produce effective vaccines for seniors. This article reviews in a succinct form the current state of the art on the development of vaccines for the elderly and critically assesses the past and current literature on this topic, while also proposing new avenues for future studies.

Correlates of protection against influenza infection in humans--on the path to a universal vaccine?

Influenza is an acute respiratory viral infection with high mutation rate and pandemic potential. Vaccination is an effective means of prevention and control of influenza, but the challenges of vaccine mismatches for the next influenza seasons and adequate global supply of influenza vaccines limit its effectiveness. Protective immunity in vaccination or natural infection is primarily mediated by antibody responses against surface proteins of influenza including haemagglutinin (HA) as the major neutralizing target, whereas strong T cell responses to internal viral proteins are associated with reduced disease severity. Recently, identification of broadly neutralizing antibodies against the conserved stem region of HA from influenza infected individuals has invigorated interest in development of a universal vaccine against different subtypes of influenza. Moreover, because of the cross-reactive nature of T cell recognition and more conserved internal antigens of influenza, strategies that boost memory T cell responses to these internal antigens may provide not only help for antibody-mediated protection but also limit the cell damage caused by viral infection directly. This is particularly important in acute infection with new pandemic viruses or antibody-escape variants where there are no pre-existing neutralizing antibodies. Here, we review the protective immune correlates against human influenza infection and discuss current status of universal influenza vaccine development.

Optimal vaccination strategies for 2009 pandemic H1N1 and seasonal influenza vaccines in humans.

A randomized clinical trial was conducted to assess whether the immunogenicity of seasonal and pandemic (H1N1/09) influenza vaccines is affected by the order of vaccine administration. 151 healthy adult volunteers were randomized into three groups. All groups received one dose (15 µg haemagglutinin) each of a pandemic H1N1 vaccine and a seasonal trivalent vaccine. Group 1 received the pandemic H1N1 vaccine first, followed by the seasonal vaccine 21 days later. Group 2 received vaccinations in vice versa and Group 3 received both vaccines simultaneously. Post-vaccination blood samples were collected to determine the immunogenicity by hemagglutination-inhibition (HI), microneutralization (MN), and B cell ELISPOT assays. All three vaccination strategies were well-tolerated and generated specific immune responses. However, we found a significant difference in magnitude of antibody responses to pandemic H1N1 between the three groups. Pre- or co-vaccination with the seasonal flu vaccine led to a significant reduction by 50% in HI titre to pandemic H1N1 virus after pandemic vaccination. Pre- or co-vaccination of pandemic H1N1 vaccine had no effect on seasonal flu vaccination. MN and ELISPOT assays showed a similar effect. Vaccination with pandemic H1N1 vaccine first is recommended to avoid an associated inhibitory effect by the seasonal trivalent flu vaccine.

A systematic molecular pathology study of a laboratory confirmed H5N1 human case.

Autopsy studies have shown that human highly pathogenic avian influenza virus (H5N1) can infect multiple human organs other than just the lungs, and that possible causes of organ damage are either viral replication and/or dysregulation of cytokines and chemokines. Uncertainty still exists, partly because of the limited number of cases analysed. In this study, a full autopsy including 5 organ systems was conducted on a confirmed H5N1 human fatal case (male, 42 years old) within 18 hours of death. In addition to the respiratory system (lungs, bronchus and trachea), virus was isolated from cerebral cortex, cerebral medullary substance, cerebellum, brain stem, hippocampus ileum, colon, rectum, ureter, aortopulmonary vessel and lymph-node. Real time RT-PCR evidence showed that matrix and hemagglutinin genes were positive in liver and spleen in addition to positive tissues with virus isolation. Immunohistochemistry and in-situ hybridization stains showed accordant evidence of viral infection with real time RT-PCR except bronchus. Quantitative RT-PCR suggested that a high viral load was associated with increased host responses, though the viral load was significantly different in various organs. Cells of the immunologic system could also be a target for virus infection. Overall, the pathogenesis of HPAI H5N1 virus was associated both with virus replication and with immunopathologic lesions. In addition, immune cells cannot be excluded from playing a role in dissemination of the virus in vivo.

Reduction of natural killer but not effector CD8 T lymphocytes in three consecutive cases of severe/lethal H1N1/09 influenza A virus infection.

BACKGROUND: The cause of severe disease in some patients infected with pandemic influenza A virus is unclear. METHODOLOGY/PRINCIPAL FINDINGS: We present the cellular immunology profile in the blood, and detailed clinical (and post-mortem) findings of three patients with rapidly progressive infection, including a pregnant patient who died. The striking finding is of reduction in natural killer (NK) cells but preservation of activated effector CD8 T lymphocytes; with viraemia in the patient who had no NK cells. Comparison with control groups suggests that the reduction of NK cells is unique to these severely ill patients. CONCLUSION/SIGNIFICANCE: Our report shows markedly reduced NK cells in the three patients that we sampled and raises the hypothesis that NK may have a more significant role than T lymphocytes in controlling viral burden when the host is confronted with a new influenza A virus subtype.

Avian influenza A(H5N1) viruses can directly infect and replicate in human gut tissues.

The human respiratory tract is a major site of avian influenza A(H5N1) infection. However, many humans infected with H5N1 present with gastrointestinal tract symptoms, suggesting that this may also be a target for the virus. In this study, we demonstrated that the human gut expresses abundant avian H5N1 receptors, is readily infected ex vivo by the H5N1 virus, and produces infectious viral particles in organ culture. An autopsy colonic sample from an H5N1-infected patient showed evidence of viral antigen expression in the gut epithelium. Our results provide the first evidence, to our knowledge, that H5N1 can directly target human gut tissues.

T cell responses to whole SARS coronavirus in humans.

Effective vaccines should confer long-term protection against future outbreaks of severe acute respiratory syndrome (SARS) caused by a novel zoonotic coronavirus (SARS-CoV) with unknown animal reservoirs. We conducted a cohort study examining multiple parameters of immune responses to SARS-CoV infection, aiming to identify the immune correlates of protection. We used a matrix of overlapping peptides spanning whole SARS-CoV proteome to determine T cell responses from 128 SARS convalescent samples by ex vivo IFN-gamma ELISPOT assays. Approximately 50% of convalescent SARS patients were positive for T cell responses, and 90% possessed strongly neutralizing Abs. Fifty-five novel T cell epitopes were identified, with spike protein dominating total T cell responses. CD8(+) T cell responses were more frequent and of a greater magnitude than CD4(+) T cell responses (p < 0.001). Polychromatic cytometry analysis indicated that the virus-specific T cells from the severe group tended to be a central memory phenotype (CD27(+)/CD45RO(+)) with a significantly higher frequency of polyfunctional CD4(+) T cells producing IFN-gamma, TNF-alpha, and IL-2, and CD8(+) T cells producing IFN-gamma, TNF-alpha, and CD107a (degranulation), as compared with the mild-moderate group. Strong T cell responses correlated significantly (p < 0.05) with higher neutralizing Ab. The serum cytokine profile during acute infection indicated a significant elevation of innate immune responses. Increased Th2 cytokines were observed in patients with fatal infection. Our study provides a roadmap for the immunogenicity of SARS-CoV and types of immune responses that may be responsible for the virus clearance, and should serve as a benchmark for SARS-CoV vaccine design and evaluation.