Cross-reaction but no avidity change of the serum antibody response after influenza vaccination

Daily preventive zinc supplementation increases the antibody response against pathogenic Escherichia coli in children with zinc insufficiency: a randomised controlled trial

Zinc deficiency impairs the antibody-mediated immune response and is common in children from lower-income countries. This study aimed to investigate the impact of different zinc supplementation regimens (7, 10 or 20 mg/day elemental zinc)—therapeutic dispersible zinc tablets (TZ), daily multiple micronutrient powder (MNP), daily preventive zinc tablets (PZ) and placebo powder (control)—and compare between baseline and endline antibody production against pathogenic Escherichia coli in Laotian children (aged 6–23 months). Fifty representative plasma samples of each treatment group were randomly selected from 512 children to determine anti-E. coli IgG antibody levels and avidity. Of the 200 children, 78.5% had zinc deficiency (plasma zinc concentration < 65 µg/dL) and 40% had anaemia before receiving zinc supplementation. aAfter receiving the TZ, MNP or PZ regimen, the plasma anti-E. coli IgG levels were significantly increased compared with baseline; the effect on the antibody level was more pronounced in children with zinc deficiency. Interestingly, there was increased anti-E. coli IgG avidity in the control and PZ groups. This study suggests that PZ might be the optimal zinc supplementation regimen to increase both the quantity and quality of antibody responses in children with zinc deficiency. Clinical trial registration: https://clinicaltrials.gov/ct2/show/NCT02428647 (NCT02428647, 29/04/2015).

Incomplete IgG avidity maturation after seasonal coronavirus infections

In classical viral infections, the avidity of immunoglobulin G (IgG) is low during acute infection and high a few months later. As recently reported, SARS-CoV-2 infections are not following this scheme, but they are rather characterized by incomplete avidity maturation. This study was performed to clarify whether infection with seasonal coronaviruses also leads to incomplete avidity maturation. The avidity of IgG toward the nucleoprotein (NP) of the seasonal coronaviruses 229E, NL63, OC43, HKU1 and of SARS-CoV-2 was determined in the sera from 88 healthy, SARS-CoV-2-negative subjects and in the sera from 70 COVID-19 outpatients, using the recomLine SARS-CoV-2 assay with recombinant antigens. In the sera from SARS-CoV-2-negative subjects, incomplete avidity maturation (persistent low and intermediate avidity indices) was the lowest for infections with the alpha-coronaviruses 229E (33.3%) and NL63 (61.3%), and the highest for the beta-coronaviruses OC43 (77.5%) and HKU1 (71.4%). In the sera from COVID-19 patients, the degree of incomplete avidity maturation of IgG toward NP of 223E, OC43, and HKU1 was not significantly different from that found in SARS-CoV-2-negative subjects, but a significant increase in avidity was observed for IgG toward NP of NL63. Though there was no cross-reaction between SARS-CoV-2 and seasonal coronaviruses, higher concentrations of IgG directed toward seasonal coronaviruses seemed to indirectly increase avidity maturation of IgG directed toward SARS-CoV-2. Our data show that incomplete IgG avidity maturation represents a characteristic consequence of coronavirus infections. This raises problems for the serological differentiation between acute and past infections and may be important for the biology of coronaviruses.

The challenge of avidity determination in SARS-CoV-2 serology

The serological responses towards severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) nucleoprotein, receptor‐binding domain (RBD), and spike protein S1 are characterized by incomplete avidity maturation. Analysis with varying concentrations of urea allows to determine distinct differences in avidity maturation, though the total process remains at an unusually low level. Despite incomplete avidity maturation, this approach allows to define early and late stages of infection. It therefore can compensate for the recently described irregular kinetic patterns of immunoglobulin M and immunoglobulin G (IgG) directed towards SARS‐CoV‐2 antigens. The serological responses towards seasonal coronaviruses neither have a negative nor positive impact on SARS‐CoV‐2 serology in general. Avidity determination in combination with measurement of antibody titers and complexity of the immune response allows to clearly differentiate between IgG responses towards seasonal coronaviruses and SARS‐CoV‐2. Cross‐reactions seem to occur with very low probability. They can be recognized by their pattern of response and through differential treatment with urea. As high avidity has been shown to be essential in several virus systems for the protective effect of neutralizing antibodies, it should be clarified whether high avidity of IgG directed towards RBD indicates protective immunity. If this is the case, monitoring of avidity should be part of the optimization of vaccination programs.

Avidity maturation of immunoglobulin G (IgG) towards severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) antigens is distinct, but incomplete in most cases

Nevertheless, avidity determination allows to differentiate between acute and past SARS CoV‐infection

Avidity maturation is instrumental for differentiation between IgG responses towards SARS‐CoV‐2 and seasonal coronaviruses

It is suggested to clarify whether high avidity is required for and indicative of protective immunity.

Increased influenza-specific antibody avidity in HIV-infected women compared with HIV-infected men on antiretroviral therapy

BACKGROUND

It is recommended that HIV-infected individuals receive annual influenza vaccination due to their high susceptibility to influenza infection, especially among women. However, there have been few studies investigating sex-related responses to influenza vaccine in antiretroviral therapy (ART)-treated HIV-infected individuals.

METHOD

In this study, 26 aviremic ART-treated HIV-infected individuals and 16 healthy controls were enrolled in the current study. Blood was collected prior to vaccination (D0), on days 7-10 (D7) and on days 14-21 (D14) following administration of the 2013-2014 seasonal influenza vaccine. A series of analyses evaluated the serological and cellular responses following influenza vaccination.

RESULTS

Female HIV-infected individuals had increased influenza-specific antibody avidity relative to male HIV-infected individuals, but similar plasma levels of influenza-specific binding antibodies and neutralizing antibodies. Increased cycling B cells and follicular helper CD4 T (Tfh) cells were observed in female HIV-infected individuals pre and postvaccination compared with male HIV-infected individuals, and cycling Tfh cells were directly correlated with influenza-specific antibody avidity. Moreover, plasma testosterone levels were inversely correlated with antibody avidity index. The magnitude of microbial translocation [plasma lipopolysaccharide (LPS)] level was directly correlated with influenza-specific antibody avidity. Circulating 16S rDNA microbiome showed that enrichment of specific species within Proteobacteria was associated with influenza-specific antibody avidity. These results, including differences based on sex and correlations, were only observed in HIV-infected individuals but not in the healthy controls.

CONCLUSION

This study demonstrated sex differences in influenza-specific antibody avidity in ART-treated HIV disease, and provides valuable information on vaccination strategy in the ART-treated HIV-infected population.

Immunostimulatory effects of truncated and full-length flagellin recombinant proteins

Problems regarding purification efficacy in recombinant technologies is due to the protein structure. Experimental manipulation of genes and the subsequent proteins may overcome this issue. In order to improve production efficacy and maintain immunestimulatory effect of flagellin, the Toll-like Receptor 5 (TLR5) ligand and a potent adjuvant, we performed a bioinformatic study to find the best model for FliC manipulation. Truncated modified FliC (tmFliC) and full length FliC (flFliC) genes were cloned and expressed in pET-21a vector and protein purification was carried out using an improved His-Tag method. Polyclonal antibodies were generated against flFliC and tmFliC in New Zealand white rabbits. IgG response to the recombinant proteins was determined by ELISA. Cross-reactivity assay was performed by ELISA for all proteins and bacteria. Immunogenicity of tmFliC and flFliC was evaluated in chicken cells, and expression level of tumor necrotic factor-α (TNF-α) and interleukin-6 (IL-6) were relatively analyzed by Real-Time-PCR. Results showed high purification efficacy for tmFliC. Antibody titer of tmFliC was significantly higher than that of flFliC. In addition, the cross-reactivity assay for both proteins and Salmonella was positive which indicates similar epitopic regions. Stimulation of both FliCs significantly increased TNF-α and IL-6 expression in peripheral blood mononuclear cells (PBMCs) and splenocytes, with higher effect observed with flFliC. IL-8 protein level increased after 6 and 24 h stimulation with different concentrations of tmFliC and flFliC. These results suggest that the aimed gene modification in fliC gene produces a bioactive immunostimulant type of flagellin which upregulates TLR5 downstream genes as well as in flFliC.

Influenza vaccine: Where are we and where do we go?

The alarming rise of morbidity and mortality caused by influenza pandemics and epidemics has drawn attention worldwide since the last few decades. This life-threatening problem necessitates the development of a safe and effective vaccine to protect against incoming pandemics. The currently available flu vaccines rely on inactivated viral particles, M2e-based vaccine, live attenuated influenza vaccine (LAIV) and virus like particle (VLP). While inactivated vaccines can only induce systemic humoral responses, LAIV and VLP vaccines stimulate both humoral and cellular immune responses. Yet, these vaccines have limited protection against newly emerging viral strains. These strains, however, can be targeted by universal vaccines consisting of conserved viral proteins such as M2e and capable of inducing cross-reactive immune response. The lack of viral genome in VLP and M2e-based vaccines addresses safety concern associated with existing attenuated vaccines. With the emergence of new recombinant viral strains each year, additional effort towards developing improved universal vaccine is warranted. Besides various types of vaccines, microRNA and exosome-based vaccines have been emerged as new types of influenza vaccines which are associated with new and effective properties. Hence, development of a new generation of vaccines could contribute to better treatment of influenza.

Boosting of Cross-Reactive and Protection-Associated T Cells in Children After Live Attenuated Influenza Vaccination

Background

Live attenuated influenza vaccines (LAIVs) stimulate a multifaceted immune response including cellular immunity, which may provide protection against newly emerging strains. This study shows proof of concept that LAIVs boost preexisting, cross-reactive T cells in children to genetically diverse influenza A virus (IAV) strains to which the children had not been exposed.

Methods

We studied the long-term cross-reactive T-cell response in 14 trivalent LAIV-vaccinated children using the fluorescent immunospot assay (FluoroSpot) with heterologous H1N1 and H3N2 IAVs and CD8+ peptides from the internal proteins (matrix protein 1 [M1], nucleoprotein [NP], polymerase basic protein 1 [PB1]). Serum antibody responses were determined by means of hemagglutination inhibition assay. Blood samples were collected before vaccination and up to 1 year after vaccination.

Results

Preexisting cross-reactive T cells to genetically diverse IAV strains were found in the majority of the children, which were further boosted in 50% of them after receipt of LAIV. Further analyses of these T cells showed significant increases in CD8+ T cells, mainly dominated by NP-specific responses. After vaccination with LAIV, the youngest children showed the highest increase in T-cell responses.

Conclusion

LAIV boosts durable, cross-reactive T-cell responses in children and may have a clinically protective effect at the population level. LAIV may be a first step toward the desired universal influenza vaccine.

Impact of Pre-exposure History and Host Genetics on Antibody Avidity Following Norovirus Vaccination

Background

Development of high avidity, broadly neutralizing antibodies (Abs) is a priority after vaccination against rapidly evolving, widely disseminated viruses like human norovirus. After vaccination with a multivalent GI.1 and GII.4c norovirus virus-like particle (VLP) vaccine candidate adjuvanted with alum and monophosphoryl lipid A (MPL), blockade Ab titers peaked early, with no increase in titer following a second vaccine dose.

Methods

Blockade Ab relative avidity was evaluated by measuring the slope of blockade Ab neutralization curves.

Results

Blockade Ab avidity to the GI.1 vaccine component peaked at day 35 (7 days after dose 2). Avidities to heterotypic genogroup I VLPs were not sustained at day 35 after vaccination or GI.1 infection, as measured from archived sera. Only secretor-positive participants maintained high avidity blockade Ab to GI.1 at day 180. Avidity to the GII.4c vaccine component peaked at day 7, remained elevated through day 180, and was not secretor dependent. Avidity to an immunologically novel GII.4 strain VLP correlated with preexisting Ab titer to an ancestral strain Epitope A.

Conclusions

Host genetics and pre-exposure history shape norovirus vaccine Ab responses, including blockade Ab avidity. Avidity of potentially neutralizing Ab may be an important metric for evaluating vaccine responses to highly penetrant viruses with cross-reactive serotypes.

Discordant correlation between serological assays observed when measuring heterosubtypic responses against avian influenza H5 and H7 viruses in unexposed individuals

The human population is constantly exposed to multiple influenza A subtypes due to zoonotic spillover and rapid viral evolution driven by intrinsic error-prone replication and immunological pressure. In this context, antibody responses directed against the HA protein are of importance since they have been shown to correlate with protective immunity. Serological techniques, detecting these responses, play a critical role for influenza surveillance, vaccine development, and assessment. As the recent human pandemics and avian influenza outbreaks have demonstrated, there is an urgent need to be better prepared to assess the contribution of the antibody response to protection against newly emerged viruses and to evaluate the extent of preexisting heterosubtypic immunity in populations. In this study, 68 serum samples collected from the Italian population between 1992 and 2007 were found to be positive for antibodies against H5N1 as determined by single radial hemolysis (SRH), but most were negative when evaluated using haemagglutination inhibition (HI) and microneutralisation (MN) assays. As a result of these discordant serological findings, the increased sensitivity of lentiviral pseudotypes was exploited in pseudotype-based neutralisation (pp-NT) assays and the results obtained provide further insight into the complex nature of humoral immunity against influenza A viruses.

Immunological assessment of influenza vaccines and immune correlates of protection

Influenza vaccines remain the primary public health tool in reducing the ever-present burden of influenza and its complications. In seeking more immunogenic, more effective and more broadly cross-protective influenza vaccines, the landscape of influenza vaccines is rapidly expanding, both in near-term advances and next-generation vaccine design. Although the first influenza vaccines were licensed over 60 years ago, the hemagglutination-inhibition antibody titer is currently the only universally accepted immune correlate of protection against influenza. However, hemagglutination-inhibition titers appear to be less effective at predicting protection in populations at high risk for severe influenza disease; older adults, young children and those with certain medical conditions. The lack of knowledge and validated methods to measure alternate immune markers of protection against influenza remain a substantial barrier to the development of more immunogenic, broadly cross-reactive and effective influenza vaccines. Here, the authors review the knowledge of immune effectors of protection against influenza and discuss assessment methods for a broader range of immunological parameters that could be considered in the evaluation of traditional or new-generation influenza vaccines.

Serum antibodies against native and denaturated hemagglutinin glycoproteins detected by ELISA as correlates of protection after influenza vaccination in healthy vaccinees and in kidney transplant recipients

The microneutralization assay is the standard method to investigate immune responses to influenza vaccination. However there remains some uncertainty as to whether ELISA results are a true measure of immunity in healthy or immuno-compromised vaccines. Furthermore it has been questioned if antibodies against native ("folded") and against denaturated ("unfolded") viral glycoproteins can equally be used as a marker of protection. In this study, two different quantitative IgG-ELISA assays detecting (i) antibodies against unfolded recombinant hemagglutinin (HA) (r-ELISA) and (ii) antibodies against the native HA on the influenza virus surface captured by fetuin-linkage (f-ELISA) were compared to microneutralization titers in sera from 29 healthy vaccinees (n=87 sera) and 39 kidney transplant recipients (n=117 sera) collected before, three weeks after and six months after vaccination against influenza A (H1N1) 2009. With both ELISAs a significant increase in antibody levels was detected after vaccination and linear regression analysis demonstrated that r-ELISA and f-ELISA correlated with microneutralization (R=0.622 for r-ELISA vs. R=0.56 for f-ELISA). For the healthy vaccinees both ELISAs were found to be adequate to distinguish protected from non-protected individuals (sensitivity and specificity: 87.5%/85.3% for r-ELISA and 87.5%/88.3% for f-ELISA). Results from the transplant recipients showed a slightly reduced sensitivity of 73.3% for r-ELISA while the f-ELISA demonstrated similar sensitivity and specificity as in the healthy vaccinees. However, in order to obtain these assay performances the cut-off-values for protection had to be adjusted for both assays and both investigation cohorts respectively limiting their application in routine laboratories.

Antibody response after single H1N1 influenza vaccine in chronic dialysis patients

The first influenza pandemic of this century happened through a rapid spread of a novel swine-derived H1N1 influenza virus. Vaccines are produced in order to avoid the infection. Children and other high risk groups are highly recommended for vaccination due to the high probability of contracting the virus. Chronic kidney disease patients were also accepted as a risk group and vaccination of all patients undergoing hemodialysis or peritoneal dialysis was recommended. The results of H1N1 influenza virus vaccine on patients receiving hemodialysis and peritoneal dialysis are analyzed. Antibody titers of both hemodialysis and peritoneal dialysis patients were elevated after vaccination. Peritoneal dialysis patients responded better.

Serologic assays for influenza surveillance, diagnosis and vaccine evaluation

Serological techniques play a critical role in various aspects of influenza surveillance, vaccine development and evaluation, and sometimes in diagnosis, particularly for novel influenza virus infections of humans. Because individuals are repeatedly exposed to antigenically and genetically diverse influenza viruses over a lifetime, the gold standard for detection of a recent influenza virus infection or response to current vaccination is the demonstration of a seroconversion, a fourfold or greater rise in antibody titer relative to a baseline sample, to a circulating influenza strain or vaccine component. The hemagglutination-inhibition assay remains the most widely used assay to detect strain-specific serum antibodies to influenza. The hemagglutination-inhibition assay is also used to monitor antigenic changes among influenza viruses which are constantly evolving; such antigenic data is essential for consideration of changes in influenza vaccine composition. The use of the hemagglutinin-specific microneutralization assay has increased, in part, owing to its sensitivity for detection of human antibodies to novel influenza viruses of animal origin. Neutralization assays using replication-incompetent pseudotyped particles may be advantageous in some laboratory settings for detection of antibodies to influenza viruses with heightened biocontainment requirements. The use of standardized protocols and antibody standards are important steps to improve reproducibility and interlaboratory comparability of results of serologic assays for influenza viruses.

Effectiveness of the AS03-adjuvanted vaccine against pandemic influenza virus A/(H1N1) 2009--a comparison of two methods; Germany, 2009/10

During the autumn wave of the pandemic influenza virus A/(H1N1) 2009 (pIV) the German population was offered an AS03-adjuvanted vaccine. The authors compared results of two methods calculating the effectiveness of the vaccine (VE). The test-negative case-control method used data from virologic surveillance including influenza-positive and negative patients. An innovative case-series methodology explored data from all nationally reported laboratory-confirmed influenza cases. The proportion of reported cases occurring in vaccinees during an assumed unprotected phase after vaccination was compared with that occurring in vaccinees during their assumed protected phase. The test-negative case-control method included 1,749 pIV cases and 2,087 influenza test-negative individuals of whom 6 (0.3%) and 36 (1.7%), respectively, were vaccinated. The case series method included data from 73,280 cases. VE in the two methods was 79% (95% confidence interval (CI) = 35–93%; P = 0.007) and 87% (95% CI = 78–92%; P<0.001) for individuals less than 14 years of age and 70% (95% CI = −45%–94%, P = 0.13) and 74% (95% CI = 64–82%; P<0.001) for individuals above the age of 14. Both methods yielded similar VE in both age groups; and VE for the younger age group seemed to be higher.

Immune responses in Atlantic salmon (Salmo salar) following protective vaccination against infectious salmon anemia (ISA) and subsequent ISA virus infection

Infectious salmon anemia (ISA) is an orthomyxoviral disease that has had devastating effects on farmed Atlantic salmon. ISA is still a disease resulting in continued loss of revenues and therefore development of effective vaccines is of great importance. Commercial vaccines against ISA are available, but the efficacy is poorly described. There is little information about vaccine-induced immune factors preventing ISA virus (ISAV) infection today. In this study we assessed the protective effects and immunogenicity of vaccines containing three different quantities of the inactivated ISAV antigen. Our findings indicated that immunization induced effective protection in Atlantic salmon with a relative percent survival (RPS) as high as 86. The level of protection was correlated to the amount of ISAV antigen in the vaccine, and fish immunized with high antigen amounts produced detectable ISAV-specific and neutralizing antibodies. While ISAV infection was detectable in non-vaccinated control fish challenged by cohabitation, no infection was detected in fish immunized with high antigen amounts. After challenge, transcriptional analysis of selected immune-related genes demonstrated activation of innate immune responses in ISAV-infected control fish, but not in vaccine protected fish. This study furthers the knowledge about vaccine efficacy and vaccine-induced immunity to ISAV challenge in Atlantic salmon.

Antibody and Th1-type cell-mediated immune responses in elderly and young adults immunized with the standard or a high dose influenza vaccine

A comparative analysis of antibody and cell-mediated immune responses was performed in ambulatory medically stable elderly and young adults who received the standard-dose of trivalent inactivated influenza vaccine, containing 15 μg of hemagglutinin (HA) per virus strain, or a high-dose vaccine containing 60 μg HA per virus strain. Among the elderly, the high dose vaccine induced greater HAI (hemagglutination inhibition) and virus neutralization antibody titers than the standard dose vaccine. These responses, however, did not achieve the magnitude of those induced by the standard dose vaccine in young adults. Vaccine-specific circulating T cells producing IFN-γ were detected in the elderly and young adults following immunization. However, there were no significant differences in the IFN-γ responses among groups. On the other hand, the standard dose vaccine in the elderly resulted in the highest proportion of complete non-responders who failed to elicit either an HAI or an IFN-γ response. This study provides further evidence that a higher dose vaccine for the elderly may result in enhanced immune responses which are predicted to improve protection although still of lower magnitude than those induced in younger healthier individuals.

How innate immune mechanisms contribute to antibody-enhanced viral infections

Preexisting antibodies may enhance viral infections. In dengue, nonneutralizing antibodies raised by natural infection with one of four dengue viruses (DENVs) may enhance infection with a different virus by a process we term "intrinsic antibody-dependent enhancement" (iADE). In addition, nonprotective antibodies raised by formalin-inactivated respiratory syncytial virus (RSV) and measles virus vaccines have led to enhanced disease during breakthrough infections. Infections under iADE conditions not only facilitate the process of viral entry into monocytes and macrophages but also modify innate and adaptive intracellular antiviral mechanisms, suppressing type 1 interferon (IFN) production and resulting in enhanced DENV replication. The suppression observed in vitro has been documented in patients with severe (dengue hemorrhagic fever [DHF]) but not in patient with mild (dengue fever [DF]) secondary dengue virus infections. Important veterinary viral infections also may exhibit iADE. It is thought that use of formalin deconforms viral epitopes of RSV, resulting in poor Toll-like receptor (TLR) stimulation; suboptimal maturation of dendritic cells with reduced production of activation factors CD40, CD80, and CD86; decreased germinal center formation in lymph nodes; and the production of nonprotective antibodies. These antibodies fail to neutralize RSV, allowing replication with secondary stimulation of RSV-primed Th2 cells producing more low-avidity antibody, resulting in immune complexes deposited into affected tissue. However, when formalin-inactivated RSV was administered with a TLR agonist to mice, they were protected against wild-type virus challenge. Safe and effective vaccines against RSV/measles virus and dengue virus may benefit from a better understanding of how innate immune responses can promote production of protective antibodies.

Heterotypic humoral and cellular immune responses following Norwalk virus infection

Norovirus immunity is poorly understood as the limited data available on protection after infection are often contradictory. In contrast to the more prominent GII noroviruses, GI norovirus infections are less frequent in outbreaks. The GI noroviruses display very complex patterns of heterotypic immune responses following infection, and many individuals are highly susceptible to reinfection. To study the immune responses and mechanisms of GI.1 persistence, we built structural models and recombinant virus-like particles (VLPs) of five GI strains: GI.1-1968, GI.1-2001, GI.2-1999, GI.3-1999, and GI.4-2000. Structural models of four GI genotype capsid P domain dimers suggested that intragenotype structural variation is limited, that the GI binding pocket is mostly preserved between genotypes, and that a conserved, surface-exposed epitope may allow for highly cross-reactive immune responses. GI VLPs bound to histo-blood group antigens (HBGAs) including fucose, Lewis, and A antigens. Volunteers infected with GI.1-1968 (n = 10) had significant increases between prechallenge and convalescent reactive IgG for all five GI VLPs measured by enzyme immunoassay. Potential cross-neutralization of GI VLPs was demonstrated by convalescent-phase serum cross-blockade of GI VLP-HBGA interaction. Although group responses were significant for all GI VLPs, each individual volunteer demonstrated a unique VLP blockade pattern. Further, peripheral blood mononuclear cells (PBMCs) were stimulated with each of the VLPs, and secretion of gamma interferon (IFN-gamma) was measured. As seen with blockade responses, IFN-gamma secretion responses differed by individual. Sixty percent responded to at least one GI VLP, with only two volunteers responding to GI.1 VLP. Importantly, four of five individuals with sufficient PBMCs for cross-reactivity studies responded more robustly to other GI VLPs. These data suggest that preexposure history and deceptive imprinting may complicate PBMC and B-cell immune responses in some GI.1-1968-challenged individuals and highlight a potential complication in the design of efficacious norovirus vaccines.

Increased antibodies against unfolded viral antigens in the elderly after influenza vaccination

Objective  Our studies aimed to measure the quality of antibody response to influenza vaccines in the elderly. The frequency of significant rise in hemagglutination inhibition (HAI) titer in the elderly is low and although annual vaccination reduces morbidity and mortality, better correlates of vaccine efficacy in the elderly are needed.

Methods  We measured the amount and avidity of serum antibodies against native H3N2 influenza glycoproteins or denatured virus (unfoldons) in pre‐ and post‐vaccinated sera of 36 elderly subjects.

Results  Eighty percent of subjects had high pre‐immunization antibody levels and only 13% showed ≥2fold increase after vaccination, but 33% showed ≥2fold increase in avidity. With increasing dosage there was a significant increase in avidity against unfoldons with 50% of subjects showing ≥2fold increase at the highest dose. Elderly subjects given subunit vaccine showed higher reactivity with unfoldons (78% of native) than younger subjects studied earlier who were given inactivated whole virus vaccine (19% of native).

Conclusion  The clear inverse relationship between pre‐immunization antibody levels and antibody increase after vaccination implies that a major reason for the low frequency of antibody responses in elderly subjects is simply because they have high pre‐immunization antibody levels. Only low reactivity was observed with earlier viruses. The increased proportion and avidity of antibodies against unfoldons is of concern, as these are not protective, and vaccine developers need to be aware of the role of age or vaccine formulation in inducing anti‐unfoldon antibodies.

Lack of antibody affinity maturation due to poor Toll-like receptor stimulation leads to enhanced respiratory syncytial virus disease

Respiratory syncytial virus (RSV) is a leading cause of hospitalization in infants. A formalin-inactivated RSV vaccine was used to immunize children in 1966 and elicited non-protective, pathogenic antibody. Two immunized infants died and 80% were hospitalized after subsequent RSV exposure. No vaccine was licensed since.

A widely accepted hypothesis attributed vaccine failure to formalin disruption of protective antigens. Instead, we show that lack of protection was not due to alterations caused by formalin, but to low antibody avidity for protective epitopes. Lack of antibody affinity maturation followed poor Toll-like receptor stimulation. This study explains why the inactivated RSV vaccine failed to protect and consequently led to severe disease, hampering vaccine development for forty-two years. Also, it suggests that inactivated RSV vaccines may be rendered safe and effective by inclusion of TLR-agonists in their formulation. In addition, it identifies affinity maturation as a critical factor for the safe immunization of infants.

Enumeration of haemagglutinin-specific CD8+ T cells after influenza vaccination using MHC class I peptide tetramers

With emergence of MHC class I tetramers loaded with CD8+ T-cell viral epitopes, it is possible to study virus-specific CD8 cells in humans during infection and after vaccination. MHC class I tetramers was used to detect the frequency of haemagglutinin (HA)-specific T cells in 26 healthy influenza-vaccinated humans. Peripheral blood was collected before, and 7, 14 and 28 days after vaccination. Four-colour flow cytometry was used for monitoring of vaccine induced T-cell response. In 15 donors, two- to fivefold increase in frequency of HA-specific T cells was observed 7 days after vaccination. In addition, in 12 of these donors, this increase was accompanied with fourfold increase of H1N1 antibody titre. The increase in frequency of HA-specific CD8+/IFN-gamma+ cells was low and peaked 28 days after vaccination in three of the six donors tested. Frequencies of HA-specific CD8+ T cells and antibody titre returned to prevaccination values 1 year after vaccination. Subunit influenza vaccines have the ability to induce HA-specific CD8+ cells. As the immune response to this vaccine decreased significantly after 1 year, our results confirm the importance of annual immunization for adequate protection.

Protection of mice from H5N1 influenza challenge by prophylactic DNA vaccination using particle mediated epidermal delivery

Mice were vaccinated with a DNA plasmid encoding the haemagglutinin (HA) antigen of H5N1 influenza A/Vietnam/1194/2004 by particle mediated epidermal delivery (PMED). Vaccination led to potent anti-HA serological responses that were significantly enhanced by the inclusion of a plasmid expressing the A and B subunits of Escherichia coli heat labile enterotoxin (designated DEI-LT). Mice were vaccinated with H5 or H5/DEI-LT and challenged with 100LD50 H5N1 A/Vietnam/1194/2004 virus. Vaccination provided considerable protection, and mice that received two doses (prime-boost) of H5/DEI-LT showed no symptoms of disease post vaccination, did not shed detectable virus and did not show any rise in anti-H5N1 HI titre post challenge, indicating that they were fully protected. These results demonstrate that the PMED technology may hold promise for the prophylaxis of pandemic influenza.

The humoral and cellular responses induced locally and systemically after parenteral influenza vaccination in man

Studies of the immune response after influenza vaccination in man, with focus on the immune activity occurring locally at mucosal surfaces and in associated lymphoid tissue, provide a valuable insight into immunity to influenza. The aim of influenza vaccination is to develop immunological memory resulting in enhanced rapid specific response upon subsequent influenza encounter. The tonsils are thought to play an important role as an activating, effector and memory site for immune responses against influenza. We have shown that normally high numbers of influenza-specific antibody secreting cells (ASC) are present in the nasal mucosa of healthy adults but upon parenteral vaccination the numbers remain stable. However, a rapid transient increase in influenza-specific ASC is observed in the tonsils and peripheral blood after vaccination. In the tonsils and blood, parenteral vaccination results in a significant decrease in CD4(+) cells upon vaccination, which are probably recruited to the draining lymph node.

Consistent patterns of change during the divergence of human immunodeficiency virus type 1 envelope from that of the inoculated virus in simian/human immunodeficiency virus-infected macaques

We have analyzed changes to proviral Env gp120 sequences and the development of neutralizing antibodies (NAbs) during 1 year of simian/human immunodeficiency virus SHIV-89.6P infection in 11 Macaca nemestrina macaques. Seven macaques had significant env divergence from that of the inoculum, and macaques with greater divergence had higher titers of homologous NAbs. Substitutions in sequons encoding potential N-linked glycosylation sites (PNGs) were among the first to be established, although overall the total number of sequons did not increase significantly. The majority (19 of 23) of PNGs present in the inoculum were conserved in the sequences from all macaques. Statistically significant variations in PNGs occurred in multiple macaques within constrained regions we term "hot spots," resulting in the selection of sequences more similar to the B consensus. These included additions on V1, the N-terminal side of V4, and the outer region of C2. Complex mutational patterns resulted in convergent PNG shifts in V2 and V5. Charge changes in Env V1V2, resulting in a net acidic charge, and a proline addition in V5 occurred in several macaques. Molecular modeling of the 89.6P sequence showed that the conserved glycans lie on the silent face of Env and that many are proximal to disulfide bonds, while PNG additions and shifts are proximal to the CD4 binding site. Nonsynonymous-to-synonymous substitution ratios suggest that these changes result from selective pressure. This longitudinal and cross-sectional study of mutations in human immunodeficiency virus (HIV) env in the SHIV background provides evidence that there are more constraints on the configuration of the glycan shield than were previously appreciated.

Amount and avidity of serum antibodies against native glycoproteins and denatured virus after repeated influenza whole-virus vaccination

There is still uncertainty on the correlates of protection by influenza vaccine. To determine the relationship between hemagglutination-inhibition (HI) titer and the specificity and avidity of serum antibodies, we analyzed serum from a longitudinal trial (1983-1987) of influenza vaccine efficacy [Keitel WA, Cate TR, Couch RB, Huggins LL, Hess KR. Efficacy of repeated annual immunization with inactivated influenza virus vaccines over a five year period. Vaccine 1997;15(10):1114-22 ]. We captured native virus particles with fetuin and separately measured relative antibody levels and avidities of antibodies against native glycoproteins and antibodies against denatured viral proteins. Most subjects had pre-existing antibodies against A/Victoria/75 and, although 70% had >two-fold increased antibodies against A/Philippines/82 after vaccination, only 30% showed increased antibodies to A/Victoria/75 indicating no dominance of original antigenic sin. There was variation in the levels of antibodies to unfolded antigens compared to native, but antibodies against denatured proteins never exceeded those against native virus. In some cases, the avidity increased without a significant increase in antibody concentration, which might explain why some vaccinees with low HI titer demonstrate adequate protection. We found that the negative correlation between pre-vaccination HI titer and the increase after vaccination is also seen when antibodies are measured directly, but that there is little relationship between HI titer and antibodies against native glycoproteins, either in amount or avidity. Our assay, which has also been adapted for recent influenza viruses that do not bind to fetuin, may be useful for vaccine evaluation.

Seroepidemiology of group C rotavirus infection in England and Wales

A total of 3199 serum samples collected in 1993--1994 from two population cohorts from England and Wales were tested for the prevalence of IgG antibodies specifically directed against group C rotavirus VP6. Seroprevalence was 39% (95% confidence intervals: 37.0-40.4%). Seroprevalence was highest (46.0%) in the oldest age group (61-70 years of age). Infection with group C rotaviruses occurred at an earlier age and with higher incidence in rural than in urban populations. These results may suggest transmission from animals to humans, however further work is required to identify the reservoir of group C rotavirus for human infection.

Influenza virus: immunity and vaccination strategies. Comparison of the immune response to inactivated and live, attenuated influenza vaccines

Influenza virus is a globally important respiratory pathogen which causes a high degree of morbidity and mortality annually. The virus is continuously undergoing antigenic change and thus bypasses the host's acquired immunity to influenza. Despite the improvement in antiviral therapy during the last decade, vaccination is still the most effective method of prophylaxis. Vaccination induces a good degree of protection (60-90% efficacy) and is well tolerated by the recipient. For those at risk of complications from influenza, annual vaccination is recommended due to the antigenic changes in circulating strains. However, there is still room for improvement in vaccine efficacy, long-lasting effect, ease of administration and compliance rates. The mucosal tissues of the respiratory tract are the main portal entry of influenza, and the mucosal immune system provides the first line of defence against infection. Secretory immunoglobulin A (SIgA) and IgM are the major neutralizing antibodies directed against mucosal pathogens. These antibodies work to prevent pathogen entry and can function intracellularly to inhibit replication of virus. This review describes influenza virus infection, epidemiology, clinical presentation and immune system response, particularly as it pertains to mucosal immunity and vaccine use. Specifically, this review provides an update of the current status on influenza vaccination and concentrates on the two main types of influenza vaccines currently in use, namely the cold-adapted vaccine (CAV) given intranasally/orally, and the inactivated vaccine (IV) delivered subcutanously or intramuscularly. The commercially available trivalent IV (TIV) elicits good serum antibody responses but induces poorly mucosal IgA antibody and cell-mediated immunity. In contrast, the CAV may elicit a long-lasting, broader immune (humoral and cellular) response, which more closely resembles natural immunity. The immune response induced by these two vaccines will be compared in this review.

Lymphocyte distribution in the tonsils prior to and after influenza vaccination

The tonsils, consisting of the adenoid, tubal, palatine and pharyngeal tonsils, form a ring like structure in humans called Waldeyer's ring. The ring of tonsils is rich in lymphocytes and may play an important role as a reservoir of memory and immune competent cells serving the respiratory tract. The tonsils may also function as an activating and effector site for immune responses against respiratory pathogens. In this study, we have examined histological tissue sections from palatine tonsils for influenza specific antibody secreting cells (ASC) and several cell surface markers, from non-vaccinated and influenza vaccinated subjects. We found an increase in the number of influenza specific ASC in the tonsils of the influenza vaccinated subjects. These ASC was found scattered inside and surrounding the germinal centres, indicating that they may have homed to the tonsils. In addition, we observed a significant decrease in CD4 positive cells in tonsils of vaccinated subjects. Similar trends were also detected for CD45RA and CD45RO positive cells, which were significantly reduced in the vaccinated tonsils. The number of macrophages bearing the CD68 surface marker increased in numbers in vaccinated subjects. This shows that dynamic changes takes place in the tonsils after parenteral influenza vaccination, which may point to an important role of the tonsils in combating respiratory pathogens.

Influenza vaccination of dialysis patients: cross-reactivity of induced haemagglutination-inhibiting antibodies to H3N2 subtype antigenic variants is comparable with the response of naturally infected young healthy adults

BACKGROUND

Annual influenza vaccination is recommended for patients with chronic renal failure, although vaccination responses in haemodialysis (HD) patients may be suboptimal. Typically, the seroreactivity has been analysed against the vaccine virus or the corresponding year's epidemic virus. No studies analysing cross-reactivity against subsequent years' viruses have been presented.

METHODS

Twenty-three chronic HD patients and 26 cardiac patients were, in autumn 1995, vaccinated with a trivalent influenza vaccine. The cross-reacting haemagglutination-inhibiting antibodies to five consecutive years' (the last season 1999-2000) drift variants of H3N2 subtype influenza A virus were measured and compared with those of vaccinated cardiac patients and with those of 26 healthy military conscripts who suffered a serologically confirmed influenza A infection in the season 1995-1996.

RESULTS

The influenza vaccination in HD patients resulted in comparable cross-reacting antibodies to the antibodies induced both by vaccination in cardiac patients and by natural infection in military conscripts. After a steady decline, the cross-reactivity to the latest epidemic virus improved in all the groups. This may be due to two reverted amino acid changes in the HA1 domain of the virus haemagglutinin.

CONCLUSIONS

Influenza vaccination in HD patients is as effective as the vaccination of cardiac patients with normal kidney function. The cross-reactivity of vaccination-induced antibodies is even as good as that of antibodies induced by natural infection of young healthy males. Additionally, vaccination seems to prime the individual beneficially against subsequent years' influenza viruses.

Analysis of the quality of protection induced by a porcine influenza A vaccine to challenge with an H3N2 virus

Antigenic drift of swine influenza A (H3N2) viruses away from the human A/Port Chalmers/1/73 (H3N2) strain, used in current commercial swine influenza vaccines, has been demonstrated in The Netherlands and Belgium. Therefore, replacement of this human strain by a more recent swine H3N2 isolate has to be considered. In this study, the efficacy of a current commercial swine influenza vaccine to protect pigs against a recent Dutch field strain (A/Sw/Oedenrode/96) was assessed. To evaluate the level of protection induced by the vaccine it was compared with the optimal protection induced by a previous homologous infection. Development of fever, virus excretion, and viral transmission to unchallenged group mates were determined to evaluate protection. The vaccine appeared efficacious in the experiment because it was able to prevent fever and virus transmission to the unchallenged group mates. Nevertheless, the protection conferred by the vaccine was sub-optimal because vaccinated pigs excreted influenza virus for a short period of time after challenge, whereas naturally immune pigs appeared completely protected. The immune response was monitored, to investigate why the vaccine conferred a sub-optimal protection. The haemagglutination inhibiting and virus neutralising antibody responses in sera, the nucleoprotein-specific IgM, IgG, and IgA antibody responses in sera and nasal secretions and the influenza-specific lymphoproliferation responses in the blood were studied. Vaccinated pigs developed the same or higher serum haemagglutination inhibiting, virus neutralising, and nucleoprotein-specific IgG antibody titres as infected pigs but lower nasal IgA titres and lymphoproliferation responses. The lower mucosal and cell-mediated immune responses may explain why protection after vaccination was sub-optimal.

High prevalence of influenza specific antibody secreting cells in nasal mucosa

Secretory immunoglobulin A (SIgA) provides the first line of defence against pathogens initiating infection via the mucosal route, e.g. the influenza virus. The aim of this study was to examine the basal level of influenza-specific antibody-secreting cell (ASC) in the local mucosa of the upper respiratory tract. Nineteen patients scheduled for tonsillectomy were enrolled for the study, and they had not experienced influenza during the previous year. Tonsils, blood, oral fluid and a nasal biopsy were sampled, and the basal levels of ASC and antibodies (Abs) were determined. We found low numbers of influenza-specific ASC in the blood and tonsils, but there were about 10-100 times higher numbers of specific ASC in the nasal mucosa tissue despite no recent influenza exposure. Thus, the basal level of influenza-specific ASC in the mucosa of the respiratory tract may be important in the protection against influenza infection.

Rapid antibody response to influenza vaccination in "at risk" groups

Persons attending for routine influenza vaccination in an urban practice each provided three specimens of blood for evaluating their immunological response. 138 (67%) of the 206 persons were defined as "at risk" by reason of morbidity as given in the guidelines published by the Chief Medical Officer. The mean age was 67 yr and 65% were aged 65 yr or more. By day 7, 71% of 31 persons had protective H(1)N(1) titres, 61% H(3)N(2) and 42% B. These proportions were similar to those found at day 14 and at day 21 based on 159 persons. These findings suggest that an effective immune response is mounted within seven days of vaccination indicating that the vaccination of persons "at risk" is worthwhile even after an epidemic has established itself. This is not a reason to modify present policy of routine vaccination in early winter well before epidemics are likely to occur.

Influenza virus subtype cross-reactivities of haemagglutination inhibiting and virus neutralising serum antibodies induced by infection or vaccination with an ISCOM-based vaccine

In order to study the levels of cross-reactivity of the influenza virus-specific antibody response upon infection or vaccination, usually hemagglutination inhibition assays are performed. In the present study post-infection ferret sera and serum samples obtained from cynomolgus macaques which were vaccinated with an ISCOM preparation based on the influenza virus strain A/Netherlands/18/94 (H3N2) were analyzed for cross-reactivity in the hemagglutination inhibition assay and in virus neutralization assays. It was shown that the cross-reactivity of the antibodies induced upon vaccination or infection with influenza virus proved to be more limited in the virus neutralization assay than in the hemagglutination assay. The strong antibody response induced by vaccination with the A/Netherlands/18/94-ISCOM preparation was shown to be cross-reactive with recent influenza virus strains, which were isolated since 1992, but not with older strains.