Haemagglutination inhibition and virus microneutralisation serology assays: use of harmonised protocols and biological standards in seasonal influenza serology testing and their impact on inter-laboratory variation and assay correlation: A FLUCOP collaborative study

Introduction

The haemagglutination inhibition assay (HAI) and the virus microneutralisation assay (MN) are long-established methods for quantifying antibodies against influenza viruses. Despite their widespread use, both assays require standardisation to improve inter-laboratory agreement in testing. The FLUCOP consortium aims to develop a toolbox of standardised serology assays for seasonal influenza. Building upon previous collaborative studies to harmonise the HAI, in this study the FLUCOP consortium carried out a head-to-head comparison of harmonised HAI and MN protocols to better understand the relationship between HAI and MN titres, and the impact of assay harmonisation and standardisation on inter-laboratory variability and agreement between these methods.

Methods

In this paper, we present two large international collaborative studies testing harmonised HAI and MN protocols across 10 participating laboratories. In the first, we expanded on previously published work, carrying out HAI testing using egg and cell isolated and propagated wild-type (WT) viruses in addition to high-growth reassortants typically used influenza vaccines strains using HAI. In the second we tested two MN protocols: an overnight ELISA-based format and a 3-5 day format, using reassortant viruses and a WT H3N2 cell isolated virus. As serum panels tested in both studies included many overlapping samples, we were able to look at the correlation of HAI and MN titres across different methods and for different influenza subtypes.

Results

We showed that the overnight ELISA and 3-5 day MN formats are not comparable, with titre ratios varying across the dynamic range of the assay. However, the ELISA MN and HAI are comparable, and a conversion factor could possibly be calculated. In both studies, the impact of normalising using a study standard was investigated, and we showed that for almost every strain and assay format tested, normalisation significantly reduced inter-laboratory variation, supporting the continued development of antibody standards for seasonal influenza viruses. Normalisation had no impact on the correlation between overnight ELISA and 3-5 day MN formats.

Long-Term Serological Investigations of Influenza A Virus in Free-Living Wild Boars (Sus scrofa) from Northern Italy (2007–2014)

Influenza A viruses (IAV) have been repeatedly demonstrated to circulate in wild suid populations. In this study, serum samples were collected from 2618 free-ranging wild boars in a protected area of Northern Italy between 2007 and 2014, and firstly screened by enzyme-linked immunosorbent assay (ELISA) for the presence of antibodies against IAV. The ELISA-positive samples were further tested by hemagglutination inhibition (HI) assays performed using antigen strains representative of the four major swine IAV (sIAV) lineages circulating in Italy: avian-like swine H1N1, pandemic-like swine H1N1, human-like swine H1N2 and human-like swine H3N2. An overall seroprevalence of 5.5% (145/2618) was detected by ELISA, with 56.7% (80/141) of screened sera tests positive by HI assay. Antibodies against H1N1 subtypes were the most prevalent beginning in 2009—with the highest detection in the first quarter of the year—until 2013, although at a low level. In addition, antibodies to H3N2 subtype were found during six years (2007, 2009, 2010, 2011, 2012 and 2014) whereas H1N2 antibodies were detected in 2012 only. Of the HI-positive samples, 30% showed reactivity to both H1N1 and H3N2 subtypes. These results provide additional insight into the circulation dynamics of IAV in wild suid populations, suggesting the occurrence of sIAV spillover events from pigs to wild boars.

Epidemiological characteristics of COVID-19 cases and estimates of the reproductive numbers 1 month into the epidemic, Italy, 28 January to 31 March 2020

BackgroundOn 20 February 2020, a locally acquired coronavirus disease (COVID-19) case was detected in Lombardy, Italy. This was the first signal of ongoing transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the country. The number of cases in Italy increased rapidly and the country became the first in Europe to experience a SARS-CoV-2 outbreak.AimOur aim was to describe the epidemiology and transmission dynamics of the first COVID-19 cases in Italy amid ongoing control measures.MethodsWe analysed all RT-PCR-confirmed COVID-19 cases reported to the national integrated surveillance system until 31 March 2020. We provide a descriptive epidemiological summary and estimate the basic and net reproductive numbers by region.ResultsOf the 98,716 cases of COVID-19 analysed, 9,512 were healthcare workers. Of the 10,943 reported COVID-19-associated deaths (crude case fatality ratio: 11.1%) 49.5% occurred in cases older than 80 years. Male sex and age were independent risk factors for COVID-19 death. Estimates of R₀ varied between 2.50 (95% confidence interval (CI): 2.18-2.83) in Tuscany and 3.00 (95% CI: 2.68-3.33) in Lazio. The net reproduction number R_t in northern regions started decreasing immediately after the first detection.ConclusionThe COVID-19 outbreak in Italy showed a clustering onset similar to the one in Wuhan, China. R₀ at 2.96 in Lombardy combined with delayed detection explains the high case load and rapid geographical spread. Overall, R_t in Italian regions showed early signs of decrease, with large diversity in incidence, supporting the importance of combined non-pharmacological control measures.

Epidemiological characteristics of COVID-19 cases and estimates of the reproductive numbers 1 month into the epidemic, Italy, 28 January to 31 March 2020

BackgroundOn 20 February 2020, a locally acquired coronavirus disease (COVID-19) case was detected in Lombardy, Italy. This was the first signal of ongoing transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the country. The number of cases in Italy increased rapidly and the country became the first in Europe to experience a SARS-CoV-2 outbreak.AimOur aim was to describe the epidemiology and transmission dynamics of the first COVID-19 cases in Italy amid ongoing control measures.MethodsWe analysed all RT-PCR-confirmed COVID-19 cases reported to the national integrated surveillance system until 31 March 2020. We provide a descriptive epidemiological summary and estimate the basic and net reproductive numbers by region.ResultsOf the 98,716 cases of COVID-19 analysed, 9,512 were healthcare workers. Of the 10,943 reported COVID-19-associated deaths (crude case fatality ratio: 11.1%) 49.5% occurred in cases older than 80 years. Male sex and age were independent risk factors for COVID-19 death. Estimates of R0 varied between 2.50 (95% confidence interval (CI): 2.18-2.83) in Tuscany and 3.00 (95% CI: 2.68-3.33) in Lazio. The net reproduction number Rt in northern regions started decreasing immediately after the first detection.ConclusionThe COVID-19 outbreak in Italy showed a clustering onset similar to the one in Wuhan, China. R0 at 2.96 in Lombardy combined with delayed detection explains the high case load and rapid geographical spread. Overall, Rt in Italian regions showed early signs of decrease, with large diversity in incidence, supporting the importance of combined non-pharmacological control measures.

Whole genome and phylogenetic analysis of two SARS-CoV-2 strains isolated in Italy in January and February 2020: additional clues on multiple introductions and further circulation in Europe

Whole genome sequences of SARS-CoV-2 obtained from two patients, a Chinese tourist visiting Rome and an Italian, were compared with sequences from Europe and elsewhere. In a phylogenetic tree, the Italian patient’s sequence clustered with sequences from Germany while the tourist’s sequence clustered with other European sequences. Some additional European sequences in the tree segregated outside the two clusters containing the patients’ sequences. This suggests multiple SARS-CoV-2 introductions in Europe or virus evolution during circulation.

Eco-Virological Preliminary Study of Potentially Emerging Pathogens in Hedgehogs (Erinaceus europaeus) Recovered at a Wildlife Treatment and Rehabilitation Center in Northern Italy

Simple Summary

Most of the newly emerging infections arise from animal reservoirs, frequently represented by wildlife species. Western European hedgehogs (Erinaceus europaeus) are mammalian hibernators, mainly nocturnal and insectivorous, living in natural open and green spaces as well as artificial, rural and urban, areas. They are generalist predators of macro-invertebrates, but they may also eat meat, bird eggs and on occasion pet food. These ecological and feeding habits, along with their high population densities, notable synanthropic attitudes, frequent contacts with sympatric wild and domestic species, including humans, implicate the possibility of intra- and interspecies interactions accounting for the possible involvement of E. europaeus in the ecology of several potentially emerging pathogens, including coronaviruses. Using PCR-based and virus isolation methods, we found that 58.3% of 24 hedgehogs’ fecal samples were PCR-positive for Erinaceus coronaviruses (EriCoVs). We did not observe any clinical disease related to the EriCoV infection in hedgehogs. However, the high mutation rates characterizing members of the Coronaviridae family and their potential successful interspecies host jumps—as that likely occurred in the Novel coronavirus (2019-nCoV) emergence—should be considered in the management of hedgehogs admitted to multi-species wildlife rehabilitation centers, recommending their return back to the original recovery areas.

Abstract

The Western European Hedgehog (Erinaceus europaeus) is one of the four hedgehog species belonging to the genus Erinaceus. Among them, E. amurensis is extant in East Asia’s areas only, whereas E. europaeus, E. roumanicus and E. concolor are mainly found in Europe. E. europaeus is endemically distributed from western to central and southern Europe, including Italy. Western European hedgehogs’ ecological and feeding habits, along with their high population densities, notable synanthropic attitudes, frequent contacts with sympatric wild and domestic species, including humans, implicate the possible involvement of E. europaeus in the ecology of potentially emerging viruses, such as coronaviruses, influenza A and influenza D viruses, canine distemper virus, pestiviruses and Aujeszky’s disease virus. We examined 24 E. europaeus individuals found injured in urban and rural areas of Northern Italy. Of the 24 fecal samples collected and tested for the above-mentioned pathogens by both PCR-based and virus isolation methods, 14 were found PCR-positive for betacoronaviruses belonging to lineage C and related to the known Erinaceus coronaviruses (EriCoVs), as determined by partial sequencing of the virus genome. Our findings suggest that hedgehogs could be considered natural reservoirs of CoVs, and also act as chronic shedding carriers of these potentially emerging RNA viruses.

Co-circulation of the two influenza B lineages during 13 consecutive influenza surveillance seasons in Italy, 2004-2017

BACKGROUND

Since 1985, two antigenically distinct lineages of influenza B viruses (Victoria-like and Yamagata-like) have circulated globally. Trivalent seasonal influenza vaccines contain two circulating influenza A strains but a single B strain and thus provide limited immunity against circulating B strains of the lineage not included in the vaccine. In this study, we describe the characteristics of influenza B viruses that caused respiratory illness in the population in Italy over 13 consecutive seasons of virological surveillance, and the match between the predominant influenza B lineage and the vaccine B lineage, in each season.

METHODS

From 2004 to 2017, 26,886 laboratory-confirmed influenza cases were registered in Italy, of which 18.7% were type B. Among them, the lineage of 2465 strains (49%) was retrieved or characterized in this study by a real-time RT-PCR assay and/or sequencing of the hemagglutinin (HA) gene.

RESULTS

Co-circulation of both B lineages was observed each season, although in different proportions every year. Overall, viruses of B/Victoria and B/Yamagata lineages caused 53.3 and 46.7% of influenza B infections, respectively. A higher proportion of infections with both lineages was detected in children, and there was a declining frequency of B/Victoria detections with age. A mismatch between the vaccine and the predominant influenza B lineage occurred in eight out of thirteen influenza seasons under study. Considering the seasons when B accounted for > 20% of all laboratory-confirmed influenza cases, a mismatch was observed in four out of six seasons. Phylogenetic analysis of the HA1 domain confirmed the co-circulation of both lineages and revealed a mixed circulation of distinct evolutionary viral variants, with different levels of match to the vaccine strains.

CONCLUSIONS

This study contributes to the understanding of the circulation of influenza B viruses in Italy. We found a continuous co-circulation of both B lineages in the period 2004-2017, and determined that children were particularly vulnerable to Victoria-lineage influenza B virus infections. An influenza B lineage mismatch with the trivalent vaccine occurred in about two-thirds of cases.

Moderate influenza vaccine effectiveness against A(H1N1)pdm09 virus, and low effectiveness against A(H3N2) subtype, 2018/19 season in Italy

Background: Influenza vaccines are updated every year to match the vaccine strains with currently circulating viruses; consequently influenza vaccine effectiveness (IVE) has to be assessed annually.Research design and methods: A test-negative case-control study was conducted within the context of the Italian sentinel influenza surveillance network to estimate IVE by age group, virus subtype, and vaccine brand in medically attended laboratory-confirmed influenza.Results: In Italy, the 2018/19 influenza season was characterized by the co-circulation of influenza A(H1N1)pdm09 and A(H3N2) viruses. The adjusted IVE estimate in preventing influenza was moderate (44.8%, 95% CI: 18.8 to 62.5) against A(H1N1)pdm09, whereas there was no evidence of effectiveness (1.8%, 95% CI: -37.8 to 30.1) in persons affected by A(H3N2). IVE against A(H1N1)pdm09 decreased with age ranging from 65.7% to 13.1% among children/adolescents and elderly, respectively; moreover results suggest that Vaxigrip Tetra® was more effective against A(H1N1)pdm09 compared to Fluarix Tetra® [62.5% (95% CI: 34.3 to 78.6) vs 24.5% (95% CI: -40.6 to 59.6)]. Low effectiveness (35.2%, 95% CI: -50.8 to 72.1) against A(H3N2) was detected only in the elderly immunized with Fluad®.Conclusions: Findings suggest that influenza vaccines were low to moderately effective, probably due to a mismatch between circulating and vaccine strains.

Virological Surveillance of Influenza in the eight epidemic seasons after the 2009 pandemic in Emilia-Romagna (Northern Italy)

BACKGROUND AND AIM OF THE WORK

Influenza virological surveillance is essential for monitoring the evolution of influenza viruses (IVs) as well as for annual updating of the vaccine composition. The aim of this study is to analyse IVs circulation in Emilia-Romagna during the eight epidemic seasons after the 2009 pandemic and to evaluate their match with seasonal vaccine strains.

METHODS

A total of 7882 respiratory specimens from patients with influenza-like illness (ILI), were collected by regional sentinel practitioners and hospital physicians. Viral investigations were conducted by rRT-PCR assay. Genetic characterization was performed for a spatial-temporal representative number of influenza laboratory-confirmed specimens.

RESULTS

Influenza-positive samples per season ranged between 28.9% (2013-2014) and 66.8% (2012-2013). Co-circulation of IVs type A and type B was observed in all seasons, although with a different intensity. In all seasons, the highest number of positive samples was recorded in younger patients aged 5-14 years with relative frequencies ranging from 40% in the 2013-2014 season and 78% in the 2012-2013 season. Since the 2009 pandemic, A/H1N1pdm09 IVs circulating were closely related to the vaccine strain A/California/7/2009. Antigenic mismatch between vaccine strain and A/H3N2 IVs was observed in the 2011-2012 and 2014-2015 seasons. During 2015-2016, 2016-2017 and 2017-2018 seasons a complete or nearly complete mismatch between the predominant influenza B lineage of IVs type B circulating and vaccine B lineage occurred.

CONCLUSIONS

This analysis confirms the importance of the virological surveillance and highlights the need of a continuous monitoring of IVs circulation, to improve the most appropriate vaccination strategies. (www.actabiomedica.it).

The epidemiological signature of influenza B virus and its B/Victoria and B/Yamagata lineages in the 21st century

We describe the epidemiological characteristics, pattern of circulation, and geographical distribution of influenza B viruses and its lineages using data from the Global Influenza B Study. We included over 1.8 million influenza cases occurred in thirty-one countries during 2000–2018. We calculated the proportion of cases caused by influenza B and its lineages; determined the timing of influenza A and B epidemics; compared the age distribution of B/Victoria and B/Yamagata cases; and evaluated the frequency of lineage-level mismatch for the trivalent vaccine. The median proportion of influenza cases caused by influenza B virus was 23.4%, with a tendency (borderline statistical significance, p = 0.060) to be higher in tropical vs. temperate countries. Influenza B was the dominant virus type in about one every seven seasons. In temperate countries, influenza B epidemics occurred on average three weeks later than influenza A epidemics; no consistent pattern emerged in the tropics. The two B lineages caused a comparable proportion of influenza B cases globally, however the B/Yamagata was more frequent in temperate countries, and the B/Victoria in the tropics (p = 0.048). B/Yamagata patients were significantly older than B/Victoria patients in almost all countries. A lineage-level vaccine mismatch was observed in over 40% of seasons in temperate countries and in 30% of seasons in the tropics. The type B virus caused a substantial proportion of influenza infections globally in the 21^st century, and its two virus lineages differed in terms of age and geographical distribution of patients. These findings will help inform health policy decisions aiming to reduce disease burden associated with seasonal influenza.

Effectiveness of the trivalent MF59 adjuvated influenza vaccine in preventing hospitalization due to influenza B and A(H1N1)pdm09 viruses in the elderly in Italy, 2017 - 2018 season

Background: Evidence on influenza vaccine effectiveness (VE) in preventing mortality and morbidity in the elderly is weak. Our aim was to measure the VE against severe outcomes in the elderly. Methods: We conducted a multicentre hospital-based test-negative design (TND) case-control study, during the 2017/18 season, in four Italian hospitals. The study population included individuals aged ≥65 years hospitalized with Severe Acute Respiratory Infections (SARI). Patients were classified as cases and controls based on the results of the PCR influenza testing. We estimated VE by virus subtypes and specific VE for the trivalent adjuvanted vaccine (TIVadj). Results: 502 patients with SARI were enrolled: 118 (23.5%) tested positive (cases) and 384 (76.5%) tested negative (controls) for influenza. The adjusted VE of 48.5% for all vaccines was comparable to the adjusted VE for the TIVadj vaccine (48.3%). Adjusted VE for the TIVadj vaccine was 67.5% for A(H1N1)pdm09 and 44.5% for B viruses. Conclusion: We show a moderate adjusted VE of the TIVadj against all viruses, a good adjusted VE against A(H1N1)pdm09 strains and a moderate adjusted VE against B strains, despite a mismatch between the B circulating lineage and the lineage included in the vaccine. This is likely due to the cross-protection among B strains induced by the TIVadj in elderly patients.

Integrase Defective Lentiviral Vector as a Vaccine Platform for Delivering Influenza Antigens

Viral vectors represent an attractive technology for vaccine delivery. We exploited the integrase defective lentiviral vector (IDLV) as a platform for delivering relevant antigens within the context of the ADITEC collaborative research program. In particular, Influenza virus hemagglutinin (HA) and nucleoprotein (NP) were delivered by IDLVs while H1N1 A/California/7/2009 subunit vaccine (HAp) with or without adjuvant was used to compare the immune response in a murine model of immunization. In order to maximize the antibody response against HA, both IDLVs were also pseudotyped with HA (IDLV-HA/HA and IDLV-NP/HA, respectively). Groups of CB6F1 mice were immunized intramuscularly with a single dose of IDLV-NP/HA, IDLV-HA/HA, HAp alone, or with HAp together with the systemic adjuvant MF59. Six months after the vaccine prime all groups were boosted with HAp alone. Cellular and antibody responses to influenza antigens were measured at different time points after the immunizations. Mice immunized with HA-pseudotyped IDLVs showed similar levels of anti-H1N1 IgG over time, evaluated by ELISA, which were comparable to those induced by HAp + MF59 vaccination, but significantly higher than those induced by HAp alone. The boost with HAp alone induced an increase of antibodies in all groups, and the responses were maintained at higher levels up to 18 weeks post-boost. The antibody response was functional and persistent overtime, capable of neutralizing virus infectivity, as evaluated by hemagglutination inhibition and microneutralization assays. Moreover, since neuraminidase (NA)-expressing plasmid was included during IDLV preparation, immunization with IDLV-NP/HA and IDLV-HA/HA also induced functional anti-NA antibodies, evaluated by enzyme-linked lectin assay. IFNγ-ELISPOT showed evidence of HA-specific response in IDLV-HA/HA immunized animals and persistent NP-specific CD8+ T cell response in IDLV-NP/HA immunized mice. Taken together our results indicate that IDLV can be harnessed for producing a vaccine able to induce a comprehensive immune response, including functional antibodies directed toward HA and NA proteins present on the vector particles in addition to a functional T cell response directed to the protein transcribed from the vector.

Correction to: Detection and full genome characterization of two beta CoV viruses related to Middle East respiratory syndrome from bats in Italy

CORRECTION

After Publication of the article [1], it has been brought to our attention that an author's name has been spelt incorrectly. The correct spelling should be "Massimo Ciccozzi", but it was previously included as "Massimo Cicozzi". The original version has now been revised to reflect this.

Detection and full genome characterization of two beta CoV viruses related to Middle East respiratory syndrome from bats in Italy

Background

Middle East respiratory syndrome coronavirus (MERS-CoV), which belongs to beta group of coronavirus, can infect multiple host species and causes severe diseases in humans. Multiple surveillance and phylogenetic studies suggest a bat origin. In this study, we describe the detection and full genome characterization of two CoVs closely related to MERS-CoV from two Italian bats, Pipistrellus kuhlii and Hypsugo savii.

Methods

Pool of viscera were tested by a pan-coronavirus RT-PCR. Virus isolation was attempted by inoculation in different cell lines. Full genome sequencing was performed using the Ion Torrent platform and phylogenetic trees were performed using IQtree software. Similarity plots of CoV clade c genomes were generated by using SSE v1.2. The three dimensional macromolecular structure (3DMMS) of the receptor binding domain (RBD) in the S protein was predicted by sequence-homology method using the protein data bank (PDB).

Results

Both samples resulted positive to the pan-coronavirus RT-PCR (IT-batCoVs) and their genome organization showed identical pattern of MERS CoV. Phylogenetic analysis showed a monophyletic group placed in the Beta2c clade formed by MERS-CoV sequences originating from humans and camels and bat-related sequences from Africa, Italy and China. The comparison of the secondary and 3DMMS of the RBD of IT-batCoVs with MERS, HKU4 and HKU5 bat sequences showed two aa deletions located in a region corresponding to the external subdomain of MERS-RBD in IT-batCoV and HKU5 RBDs.

Conclusions

This study reported two beta CoVs closely related to MERS that were obtained from two bats belonging to two commonly recorded species in Italy (P. kuhlii and H. savii). The analysis of the RBD showed similar structure in IT-batCoVs and HKU5 respect to HKU4 sequences. Since the RBD domain of HKU4 but not HKU5 can bind to the human DPP4 receptor for MERS-CoV, it is possible to suggest also for IT-batCoVs the absence of DPP4-binding potential. More surveillance studies are needed to better investigate the potential intermediate hosts that may play a role in the interspecies transmission of known and currently unknown coronaviruses with particular attention to the S protein and the receptor specificity and binding affinity.

Quantitative Multiplexed Imaging Analysis Reveals a Strong Association between Immunogen-Specific B Cell Responses and Tonsillar Germinal Center Immune Dynamics in Children after Influenza Vaccination

Generation of Ag-specific humoral responses requires the orchestrated development and function of highly specialized immune cells in secondary lymphoid organs. We used a multiparametric approach combining flow cytometry, confocal microscopy, and histocytometry to analyze, for the first time to our knowledge in children, tonsils from seasonal influenza-vaccinated children. We used these novel imaging assays to address the mucosal immune dynamics in tonsils investigating the spatial positioning, frequency, and phenotype of immune cells after vaccination. Vaccination was associated with a significantly higher frequency of follicular helper CD4 T cells compared with the unvaccinated control group. The imaging analysis revealed that potential suppressor (FOXP3^hi) CD4 T cells are mainly located in extrafollicular areas. Furthermore, a significantly reduced frequency of both follicular and extrafollicular FOXP3^hi CD4 T cells was found in the vaccine group compared with the control group. Levels of circulating CXCL13 were higher in those vaccinated compared with controls, mirroring an increased germinal center reactivity in the tonsils. Notably, a strong correlation was found between the frequency of tonsillar T follicular helper cells and tonsillar Ag-specific Ab-secreting cells. These data demonstrate that influenza vaccination promotes the prevalence of relevant immune cells in tonsillar follicles and support the use of tonsils as lymphoid sites for the study of germinal center reactions after vaccination in children.

Generation of switched memory B cells in response to vaccination in Down syndrome children and their siblings

BACKGROUND

Immunodeficiency is an integral aspect of Down syndrome, as demonstrated by the increased susceptibility to infection of affected. Mortality is still higher than in general population, with respiratory infections among the major causes of death. As more people with Down syndrome are living today than ever before, it is indispensable to develop strategies to prevent and cure the associated disorders. Vaccination is the most successful instrument of preventive medicine. Special seasonal influenza and pneumococcal vaccination strategies have been designed for individuals with risk conditions of all ages. Down syndrome individuals are not included in the high-risk categories.

METHODS

We enrolled in our study 15 children with Down syndrome and their siblings, vaccinated for the first time with seasonal influenza vaccine and receiving a booster dose of a glyco-conjugated pneumococcal vaccine. We compared the immunological features and response to vaccination measuring serum antibody titers and frequency of specific memory B cells.

RESULTS

We confirm that a severe reduction of switched memory B cells is always associated to Down syndrome. After primary vaccination Down syndrome children generate significantly less specific switched memory B cells than their siblings. The response to a booster dose of vaccine is instead comparable in both groups. The production of specific antibodies was equally effective in Down syndrome and controls both after primary and secondary immunization.

CONCLUSIONS

Down syndrome individuals should be considered a high risk group, because of their increased susceptibility to infection and reduced number of switched memory B cells. Tailored vaccination protocols are needed in order to reduce their burden of infections throughout life.

Human infection with highly pathogenic A(H7N7) avian influenza virus, Italy, 2013

During an influenza A(H7N7) virus outbreak among poultry in Italy during August–September 2013, infection with a highly pathogenic A(H7N7) avian influenza virus was diagnosed for 3 poultry workers with conjunctivitis. Genetic analyses revealed that the viruses from the humans were closely related to those from chickens on affected farms.

Vaccination for seasonal influenza in patients with cancer: recommendations of the Italian Society of Medical Oncology (AIOM)

Background

Influenza virus causes annual epidemics in the winter–spring season with significant morbidity in the general population and important mortality in high-risk groups, including cancer patients. Opinions on the suitability of patients with malignancies not undergoing active treatment and in different phases of antineoplastic therapy, to receive influenza vaccination, vary considerably among oncologists, sometimes even within one center.

Methods

We reviewed available data, including recommendations by national health authorities, on impact of influenza in patients with cancer and their capacity to mount protective immunological responses to vaccination, thus allowing, on behalf of Italian Association of Medical Oncology, to make suitable recommendations for the prevention and treatment of seasonal influenza.

Results and discussion

Patients with cancer often have disease- or treatment-related immunosuppression, and as a consequence, they may have a suboptimal serologic response to influenza vaccination. The protective effect of the different preparations of influenza vaccines in patients with cancer has not been widely investigated, especially in adult patients harboring solid tumors. The optimal timing for administration of influenza vaccines in patients receiving chemotherapy is also not clearly defined. However, since vaccination is the most effective method, along with antiviral drugs in selected patients, for preventing influenza infection, it has to be recommended for cancer patients. Implementing vaccination of close contacts of oncology patients would be an additional tool for enhancing protection in fragile patient populations.

Antibody but not memory B-cell responses are tuned-down in vertically HIV-1 infected children and young individuals being vaccinated yearly against influenza

Yearly immunization against seasonal influenza is highly recommended for HIV-1 infected individuals but evaluating the success of vaccination by serological markers may not be fully informative in this population. Recently, it has been hypothesized that the generation of long-lasting immune responses may depend on whether similar antigens challenge the immune system frequently and intermittently. In the present study, in order to search for additional correlates of vaccine-induced protective immunity and to further dissect this theory, both humoral and memory B-cell responses to the trivalent 2012-2013 seasonal influenza vaccination has been evaluated by strain-specific (separately for H1N1, H3N2 and B strain) standard hemagglutination inhibition (HI) assay and B-cell enzyme-linked immunosorbent spot (ELISpot) in a cohort of vertically HIV-1 infected children and young individuals as compared to age-matched healthy controls. A high number of HIV-1 infected individuals had protective antibody levels prior to vaccination and showed low seroconversion rates after vaccination as compared to healthy controls. On the contrary, similar frequencies of influenza-specific memory B-cells were detected by B-cell ELISpot in both groups suggesting that an adequate B-cell response has been elicited. Data from the H1N1 strain, which is recurrent in seasonal influenza vaccines since 2009, pointed out decreasing antibody but not memory B-cell responses for HIV-1 infected patients being vaccinated for a greater number of years. Further investigations are required to standardize the influenza-specific B-cell ELISpot and to understand whether it could be used routinely as an additional tool to evaluate response to influenza vaccination in immune-compromised individuals being vaccinated yearly.

Investigation of an imported case of Middle East Respiratory Syndrome Coronavirus (MERS-CoV) infection in Florence, Italy, May to June 2013

On 31 May 2013, the first case of Middle East Respiratory Syndrome Coronavirus (MERS-CoV) infection in Italy was laboratory confirmed in a previously healthy adult man, who developed pneumonia with moderate respiratory distress after returning from a holiday in Jordan. Two secondary cases were identified through contact tracing, among family members and colleagues who had not previously travelled abroad. Both secondary cases developed mild illness. All three patients recovered fully.

Efficient vagina-to-lower respiratory tract immune trafficking in a murine model of influenza A virus infection

Effective vaccination strategies for infectious diseases take into account the induction, long-term maintenance and recall of memory T-cell populations. To understand the immunological cross-talk within the mucosal compartments, we compared intranasal to vaginal immunization and demonstrated that vaginal infection of BALB/c mice with influenza A virus provides protective mucosal immunity against both homosubtypic and heterosubtypic virus challenge in the respiratory tract. We found that, prior to the viral challenge, in vaginally primed mice, antigen-specific CD8+ T cells were not detected in the lung airways and levels of serum antibodies were lower than those observed in intranasally immunized mice. However, following pulmonary challenge, NP147-specific CD8+ T cells were recruited and amplified in vaginally primed mice to the same extent as those in intranasally primed mice. Thus, the long-term memory immune response elicited by vaginal immunization with influenza virus is efficiently recalled and offers reasonable protection against infection in the respiratory tract.

The role of antigen in the localization of naive, acutely activated, and memory CD8(+) T cells to the lung during influenza pneumonia

The role of Ag in the recruitment and localization of naive, acutely activated, and memory CD8(+) T cells to the lung during influenza infection was explored using TCR-transgenic (Tg) mice. Naive, Thy1.2(+)CD8(+) OT-I TCR-Tg cells were primed and recruited to the lung after transfer into congenic Thy1.1(+) recipients challenged with a genetically engineered influenza virus (influenza A/WSN/33 (WSN)-OVA(I)) containing the K(b) restricted OVA(257-264) epitope (siinfekl) in the viral neuraminidase stalk. However, if the transferred animals were infected with a similar influenza virus that expressed an irrelevant K(b) epitope (WSN-PEPII), no TCR-Tg T cells were detectable in the lung, although they were easily visible in the lymphoid organs. Conversely, there were substantial numbers of OT-I cells found in the lungs of WSN-PEPII-infected mice when the animals had been previously, or were concurrently, infected with a recombinant vaccinia virus expressing OVA. Similar results were obtained with nontransgenic populations of memory CD8(+) T cells reactive to a murine gamma-herpesvirus-68 Ag. Interestingly, the primary host response to the immunodominant influenza nucleoprotein epitope was not affected by the presence of memory or recently activated OT-I T cells. Thus, although Ag is required to activate the T cells, the subsequent localization of T cells to the lung during a virus infection is a property of recently activated and memory T cells and is not necessarily driven by Ag in the lung.

Early alterations of the receptor-binding properties of H1, H2, and H3 avian influenza virus hemagglutinins after their introduction into mammals

Interspecies transmission of influenza A viruses circulating in wild aquatic birds occasionally results in influenza outbreaks in mammals, including humans. To identify early changes in the receptor binding properties of the avian virus hemagglutinin (HA) after interspecies transmission and to determine the amino acid substitutions responsible for these alterations, we studied the HAs of the initial isolates from the human pandemics of 1957 (H2N2) and 1968 (H3N2), the European swine epizootic of 1979 (H1N1), and the seal epizootic of 1992 (H3N3), all of which were caused by the introduction of avian virus HAs into these species. The viruses were assayed for their ability to bind the synthetic sialylglycopolymers 3'SL-PAA and 6'SLN-PAA, which contained, respectively, 3'-sialyllactose (the receptor determinant preferentially recognized by avian influenza viruses) and 6'-sialyl(N-acetyllactosamine) (the receptor determinant for human viruses). Avian and seal viruses bound 6'SLN-PAA very weakly, whereas the earliest available human and swine epidemic viruses bound this polymer with a higher affinity. For the H2 and H3 strains, a single mutation, 226Q-->L, increased binding to 6'SLN-PAA, while among H1 swine viruses, the 190E-->D and 225G-->E mutations in the HA appeared important for the increased affinity of the viruses for 6'SLN-PAA. Amino acid substitutions at positions 190 and 225 with respect to the avian virus consensus sequence are also present in H1 human viruses, including those that circulated in 1918, suggesting that substitutions at these positions are important for the generation of H1 human pandemic strains. These results show that the receptor-binding specificity of the HA is altered early after the transmission of an avian virus to humans and pigs and, therefore, may be a prerequisite for the highly effective replication and spread which characterize epidemic strains.

Balanced hemagglutinin and neuraminidase activities are critical for efficient replication of influenza A virus

The SD0 mutant of influenza virus A/WSN/33 (WSN), characterized by a 24-amino-acid deletion in the neuraminidase (NA) stalk, does not grow in embryonated chicken eggs because of defective NA function. Continuous passage of SD0 in eggs yielded 10 independent clones that replicated efficiently. Characterization of these egg-adapted viruses showed that five of the viruses contained insertions in the NA gene from the PB1, PB2, or NP gene, in the region linking the transmembrane and catalytic head domains, demonstrating that recombination of influenza viral RNA segments occurs relatively frequently. The other five viruses did not contain insertions in this region but displayed decreased binding affinity toward sialylglycoconjugates, compared with the binding properties of the parental virus. Sequence analysis of one of the latter viruses revealed mutations in the hemagglutinin (HA) gene, at sites in close proximity to the sialic acid receptor-binding pocket. These mutations appear to compensate for reduced NA function due to stalk deletions. Thus, balanced HA-NA functions are necessary for efficient influenza virus replication.

Postexposure vaccination massively increases the prevalence of gamma-herpesvirus-specific CD8+ T cells but confers minimal survival advantage on CD4-deficient mice

Mice that lack CD4(+) T cells remain clinically normal for more than 60 days after respiratory challenge with the murine gamma-herpesvirus 68 (gammaHV-68), then develop symptoms of a progressive wasting disease. The gammaHV-68-specific CD8(+) T cells that persist in these I-A(b-/-) mice are unable to prevent continued, but relatively low level, virus replication. Postexposure challenge with recombinant vaccinia viruses expressing gammaHV-68 lytic cycle epitopes massively increased the magnitude of the gammaHV-68-specific CD8(+) population detectable by staining with tetrameric complexes of MHC class I glycoprotein + peptide, or by interferon-gamma production subsequent to in vitro restimulation with peptide. The boosting effect was comparable for gammaHV-68-infected I-A(b-/-) and I-A(b+/+) mice within 7 days of challenge, and took more than 110 days to return to prevaccination levels in the I-A(b+/+) controls. Although the life-span of the I-A(b-/-) mice was significantly increased, there was no effect on long-term survival. A further boost with a recombinant influenza A virus failed to improve the situation. Onset of weight loss was associated with a decline in gammaHV-68-specific CD8(+) T cell numbers, though it is not clear whether this was a cause or an effect of the underlying pathology. Even very high levels of virus-specific CD8(+) T cells thus provide only transient protection against the uniformly lethal consequences of gammaHV-68 infection under conditions of CD4(+) T cell deficiency.

A gamma-herpesvirus sneaks through a CD8(+) T cell response primed to a lytic-phase epitope

To determine whether established CD8(+) T cell memory to an epitope prominent during the replicative phase of a gamma-herpesvirus infection protects against subsequent challenge, mice were primed with a recombinant vaccinia virus expressing the p56 peptide and then boosted by intranasal exposure to an influenza A virus incorporating p56 in the neuraminidase protein. Clonally expanded populations of functional, p56-specific CD8(+) T cells were present at high frequency in both the lung and the lymphoid tissue 1 month later, immediately before respiratory challenge with gammaHV-68. This prime-and-boost regime led to a massive reduction of productive gammaHV-68 infection in the respiratory tract and, initially, to much lower levels of latency in both the regional lymph nodes and the spleen. The CD8(+) T cell response to another epitope (p79) was diminished, there was less evidence of B cell activation, and the onset of the CD4(+) T cell-dependent splenomegaly was delayed. Within 3-4 weeks of the gammaHV-68 challenge, however, the extent of latent infection in the lymph nodes and spleen was equivalent, and both groups developed the prominent infectious mononucleosis-like syndrome that is characteristic of this infection. The reverse protocol (influenza then vaccinia) seemed to be slightly less effective. Even though immune CD8(+) T cells may be present at the time and site of virus challenge, establishing a high level of CD8(+) T cell memory to lytic-phase epitopes alone does not protect against the longer-term consequences of this gammaHV infection.

Amino acid residues contributing to the substrate specificity of the influenza A virus neuraminidase

Influenza A viruses possess two glycoprotein spikes on the virion surface: hemagglutinin (HA), which binds to oligosaccharides containing terminal sialic acid, and neuraminidase (NA), which removes terminal sialic acid from oligosaccharides. Hence, the interplay between these receptor-binding and receptor-destroying functions assumes major importance in viral replication. In contrast to the well-characterized role of HA in host range restriction of influenza viruses, there is only limited information on the role of NA substrate specificity in viral replication among different animal species. We therefore investigated the substrate specificities of NA for linkages between N-acetyl sialic acid and galactose (NeuAcalpha2-3Gal and NeuAcalpha2-6Gal) and for different molecular species of sialic acids (N-acetyl and N-glycolyl sialic acids) in influenza A viruses isolated from human, avian, and pig hosts. Substrate specificity assays showed that all viruses had similar specificities for NeuAcalpha2-3Gal, while the activities for NeuAcalpha2-6Gal ranged from marginal, as represented by avian and early N2 human viruses, to high (although only one-third the activity for NeuAcalpha2-3Gal), as represented by swine and more recent N2 human viruses. Using site-specific mutagenesis, we identified in the earliest human virus with a detectable increase in NeuAcalpha2-6Gal specificity a change at position 275 (from isoleucine to valine) that enhanced the specificity for this substrate. Valine at position 275 was maintained in all later human viruses as well as swine viruses. A similar examination of N-glycolylneuraminic acid (NeuGc) specificity showed that avian viruses and most human viruses had low to moderate activity for this substrate, with the exception of most human viruses isolated between 1967 and 1969, whose NeuGc specificity was as high as that of swine viruses. The amino acid at position 431 was found to determine the level of NeuGc specificity of NA: lysine conferred high NeuGc specificity, while proline, glutamine, and glutamic acid were associated with lower NeuGc specificity. Both residues 275 and 431 lie close to the enzymatic active site but are not directly involved in the reaction mechanism. This finding suggests that the adaptation of NA to different substrates occurs by a mechanism of amino acid substitutions that subtly alter the conformation of NA in and around the active site to facilitate the binding of different species of sialic acid.

The role of influenza A virus hemagglutinin residues 226 and 228 in receptor specificity and host range restriction

Influenza A viruses can be isolated from a variety of animals, but their range of hosts is restricted. For example, human influenza viruses do not replicate in duck intestine, the major replication site of avian viruses in ducks. Although amino acids at positions 226 and 228 of hemagglutinin (HA) of the H3 subtype are known to be important for this host range restriction, the contributions of specific amino acids at these positions to restriction were not known. Here, we address this issue by generating HAs with site-specific mutations of a human virus that contain different amino acid residues at these positions. We also let ducks select replication-competent viruses from a replication-incompetent virus containing a human virus HA by inoculating animals with 10(10.5) 50% egg infectious dose of the latter virus and identified a mutation in the HA. Our results showed that the Ser-to-Gly mutation at position 228, in addition to the Leu-to-Gln mutation at position 226 of the HA of the H3 subtype, is critical for human virus HA to support virus replication in duck intestine.

Molecular basis for the generation in pigs of influenza A viruses with pandemic potential

Genetic and biologic observations suggest that pigs may serve as "mixing vessels" for the generation of human-avian influenza A virus reassortants, similar to those responsible for the 1957 and 1968 pandemics. Here we demonstrate a structural basis for this hypothesis. Cell surface receptors for both human and avian influenza viruses were identified in the pig trachea, providing a milieu conducive to viral replication and genetic reassortment. Surprisingly, with continued replication, some avian-like swine viruses acquired the ability to recognize human virus receptors, raising the possibility of their direct transmission to human populations. These findings help to explain the emergence of pandemic influenza viruses and support the need for continued surveillance of swine for viruses carrying avian virus genes.

Influence of host species on the evolution of the nonstructural (NS) gene of influenza A viruses

The matrix (M) and nonstructural (NS) genes of influenza A viruses each encode two overlapping proteins. In the M gene, evolution of one protein affects that of the other. To determine whether or not this evolutionary influence operating between the two M proteins also occurs in the NS gene, we sequenced the NS genes of 36 influenza A viruses isolated from a broad spectrum of animal species (wild and domestic birds, horses, pigs, humans, and sea mammals) and analyzed them phylogenetically, together with other previously published sequences. These analyses enabled us to conclude the following host species-related points that are not found in the other influenza A virus genes and their gene products. (1) The evolution of the two overlapping proteins encoded by the NS gene are lineage-dependent, unlike the M gene where evolutionary constraints on the Ml protein affect the evolution of the M2 protein (Ito et al.. J. Virol. 65 (1991) 5491 5498). (2) The gull-specific lineage contained nonH13 gull viruses and the non-gull avian lineage contained H13 gull viruses, indicating that the gull-specific lineage does not link to the H13 HA subtype in the NS gene unlike findings with other genes. (3) The branching topology of the recent equine lineage (H7N7 viruses isolated after 1973 and H3N8) indicates recent introduction of the NS, M, and PB2 genes into horses from avian sources by genetic reassortment.

The M2 ectodomain is important for its incorporation into influenza A virions

M2 is an integral protein of influenza A virus that functions as an ion channel. The ratio of M2 to HA in influenza A virions differs from that found on the cell surface, suggesting selective incorporation of M2 and HA into influenza virions. To examine the sequences that are important for M2 incorporation into virions, we used an incorporation assay that involves expressing M2 from a plasmid, transfecting the plasmid into recipient cells, and then infecting those cells with influenza virus. To test the importance of the different regions of the protein (extracellular, transmembrane, and cytoplasmic) in determining M2 incorporation, we created chimeric mutants of M2 and Sendai virus F proteins, exchanging corresponding extracellular, transmembrane, and cytoplasmic domains. Of the six possible chimeric mutants, only three were expressed on the cell surface. Of these three chimeric proteins, only one mutant (with the extracellular domain from M2 and the rest from F) was incorporated into influenza virions. These results suggest that the extracellular domain of M2 is important for its incorporation into virions.

Nuclear import and export of influenza virus nucleoprotein

Influenza virus nucleoprotein (NP) shuttles between the nucleus and the cytoplasm. A nuclear localization signal (NLS) has been identified in NP at amino acids 327 to 345 (J. Davey et al., Cell 40:667-675, 1985). However, some NP mutants that lack this region still localize to the nucleus, suggesting an additional NLS in NP. We therefore investigated the nucleocytoplasmic transport of NP from influenza virus A/WSN/33 (H1N1). NP deletion constructs lacking the 38 N-terminal amino acids, as well as those lacking the 38 N-terminal amino acids and the previously identified NLS, localized to both the cytoplasm and the nucleus. Nuclear localization of a protein containing amino acids 1 to 38 of NP fused to LacZ proved that these 38 amino acids function as an NLS. Within this region, we identified two basic amino acids, Lys7 and Arg8, that are crucial for NP nuclear import. After being imported into the nucleus, the wild-type NP and the NP-LacZ fusion construct containing amino acids 1 to 38 of NP were both transported back to the cytoplasm, where they accumulated. These data indicate that NP has intrinsic structural features that allow nuclear import, nuclear export, and cytoplasmic accumulation in the absence of any other viral proteins. Further, the information required for nuclear import and export is located in the 38 N-terminal amino acids of NP, although other NP nuclear export signals may exist. Treatment of cells with a protein kinase C inhibitor increased the amounts of nuclear NP, whereas treatment of cells with a phosphorylation stimulator increased the amounts of cytoplasmic NP. These findings suggest a role of phosphorylation in nucleocytoplasmic transport of NP.

The cysteine residues of the M2 protein are not required for influenza A virus replication

The M2 protein of influenza A virus functions as an ion channel. It contains three cysteine residues: cysteines 17 and 19, which form disulfide bonds in the ectodomain, and cysteine 50 which is acylated. To understand the role of these cysteine residues in virus replication, we used reverse genetics to create influenza viruses in which the individual cysteines were mutated and a virus in which all three cysteines were changed to serine. The M2 cysteine mutants that lacked either of the cysteine residues in the ectodomain and the mutant that lacked all three residues had appreciably lower amounts of M2 oligomers than did the wild-type virus when examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. None of the mutants, however, were defective in replication, either in vitro or in ferrets and mice. These findings demonstrate that noncovalent interactions are sufficient for the M2 protein to form functional oligomers for virus replication and that its cysteine residues are dispensable for influenza virus replication in vitro and in vivo.

HEL-Flu: an influenza virus containing the hen egg lysozyme epitope recognized by CD4+ T cells from mice transgenic for an alphabeta TCR

Reverse genetics was used to modify the influenza virus genome by inserting the p46-63 sequence of hen egg lysozyme (HEL) into the neuraminidase stalk of the virus. The resulting virus, HEL-Flu, contained the epitopes recognized by CD4+ T cells from 3A9-TCR transgenic mice (C3HTg). Here, we show that HEL-Flu was infectious in the respiratory tract of both C3H and C3HTg mice, the latter animals showing an early, transient morbidity. Splenic dendritic cells and certain cloned populations of splenic macrophages and brain microglia constitutively presented infectious and inactivated HEL-Flu to the T cells in an Ag-specific and MHC class II-restricted manner. These results demonstrate the utility of HEL-Flu in assessing the APC activity for naive T cells; they also extend the previous studies showing that discrete populations of macrophages and microglia constitutively process and present Ag to naive T cells.

HEL-Flu: an influenza virus containing the hen egg lysozyme epitope recognized by CD4+ T cells from mice transgenic for an alphabeta TCR

Reverse genetics was used to modify the influenza virus genome by inserting the p46-63 sequence of hen egg lysozyme (HEL) into the neuraminidase stalk of the virus. The resulting virus, HEL-Flu, contained the epitopes recognized by CD4+ T cells from 3A9-TCR transgenic mice (C3HTg). Here, we show that HEL-Flu was infectious in the respiratory tract of both C3H and C3HTg mice, the latter animals showing an early, transient morbidity. Splenic dendritic cells and certain cloned populations of splenic macrophages and brain microglia constitutively presented infectious and inactivated HEL-Flu to the T cells in an Ag-specific and MHC class II-restricted manner. These results demonstrate the utility of HEL-Flu in assessing the APC activity for naive T cells; they also extend the previous studies showing that discrete populations of macrophages and microglia constitutively process and present Ag to naive T cells.

Continued evolution of H1N1 and H3N2 influenza viruses in pigs in Italy

Swine influenza viruses possessing avian genes were first detected in Europe in 1979 (Scholtissek et al., 1983, Virology, 129, 521-523) and continue to circulate in pigs in that region of the world. To characterize the molecular epidemiology of swine influenza viruses currently circulating in Europe, we used dot-blot hybridization and sequence analysis to determine the origin of the genes encoding the nonsurface proteins ("internal" genes) of 10 H1N1 and 11 H3N2 swine influenza viruses isolated in Italy between 1992 and 1995. All of the 126 genes examined were of avian origin; thus the currently circulating H3N2 strains which possess A/Port Chalmers/1/73-like surface glycoproteins appear to be descendants of the reassortant human-avian viruses that emerged between 1983 and 1985 in Italy. Sequence analysis of matrix (M), nonstructural, and nucleoprotein genes, as well as phylogenetic analysis of M gene showed that the H1N1 and H3N2 viruses from the pigs were closely related to recent isolates of the avian-like swine H1N1 influenza strain currently circulating in northern Europe and were distinguishable from the genes of viruses isolated from European swine in 1979. To evaluate the frequency of transmission of swine H1N1 and H3N2 viruses to man, we tested 123 human sera for hemagglutination-inhibiting antibodies against avian and mammalian H1N1 and H3N2 virus strains. Our findings indicate that swine influenza viruses possessing A/Port Chalmers/1/73-like hemagglutinin may have transmitted to approximately 20% of young persons under 20 years of age who had contact with pigs. Thus, H3N2 swine viruses, possibly possessing avian-derived internal genes, may be entering humans more often than was previously thought. We strongly recommend that pigs be regularly monitored as a potential early warning system for detection of future pandemic strains.

Immunogenicity of influenza vaccine (1993-94 winter season) in HIV-seropositive and -seronegative ex-intravenous drug users

The humoral response (haemagglutination inhibiting antibodies) to trivalent split influenza vaccine for the 1993-94 winter season (A/Beijing/32/92 (H3N2), A/Singapore/6/86 (H1N1) and B/Panama/45/90) was evaluated in a group of young HIV-seropositive ex-intravenous heroin users and compared with responses measured in HIV-seronegative individuals with a similar history. HIV-negative volunteers showed an overall positive response suggesting that previous heroin use did not influence their humoral response to influenza vaccine. Comparable results were obtained in HIV-positive subjects with CD4+ lymphocyte counts > 500 microliters-1, whereas impaired reactivity was found in HIV-positive volunteers with CD4+ counts < 500 microliters-1. Booster vaccination did not increase antibody levels in any of the groups studied, although the data did not exclude a positive influence of a second vaccine dose on persistence of antibody at 120 days after the first dose. No significant changes were observed in p24 antigenemia levels in HIV-positive individuals after vaccination.

The cytoplasmic tail of influenza A virus neuraminidase (NA) affects NA incorporation into virions, virion morphology, and virulence in mice but is not essential for virus replication

In this study, we investigated the role of the conserved neuraminidase (NA) cytoplasmic tail residues in influenza virus replication. Mutants of influenza A virus (A/WSN/33 [H1N1]) with deletions of the NA cytoplasmic tail region were generated by reverse genetics. The resulting viruses, designated NOTAIL, contain only the initiating methionine of the conserved six amino-terminal residues. The mutant viruses grew much less readily and produced smaller plaques than did the wild-type virus. Despite similar levels of NA cell surface expression by the NOTAIL mutants and wild-type virus, incorporation of mutant NA molecules into virions was decreased by 86%. This reduction resulted in less NA activity per virion, leading to the formation of large aggregates of progeny mutant virions on the surface of infected cells. A NOTAIL virus containing an additional mutation (Ser-12 to Pro) in the transmembrane domain incorporated three times more NA molecules into virions than did the NOTAIL parent but approximately half of the amount incorporated by the wild-type virus. However, aggregation of the progeny virions still occurred at the cell surface. All NOTAIL viruses were attenuated in mice. We conclude that the cytoplasmic tail of NA is not absolutely essential for virus replication but exerts important effects on the incorporation of NA into virions and thus on the aggregation and virulence of progeny virus. In addition, the relative abundance of long filamentous particles formed by the NOTAIL mutants, compared with the largely spherical wild-type particles, indicates a role for the NA cytoplasmic tail in virion morphogenesis.

Reverse genetics system for generation of an influenza A virus mutant containing a deletion of the carboxyl-terminal residue of M2 protein

We established a reverse genetics system for the M gene of influenza A virus, using amantadine resistance as a selection criterion. Transfection of an artificial M ribonucleoprotein complex of A/Puerto Rico/8/34 (H1N1), a naturally occurring amantadine-resistant virus, and superinfection with amantadine-sensitive A/equine/Miami/1/63 (H3N8), followed by cultivation in the presence of the drug, led to the generation of a transfectant virus with the A/Puerto Rico/8/34 (H1N1) M gene. With this system, we attempted to generate a virus containing a deletion in an M-gene product (M2 protein). Viruses lacking the carboxyl-terminal Glu of M2, but not those lacking 5 or 10 carboxyl-terminal residues, were rescued in the presence of amantadine. These findings indicate that carboxyl-terminal residues of the M2 protein play an important role in influenza virus replication. The M-gene-based reverse genetics system will allow the study of different M-gene mutations to achieve a balance between attenuation and virus replication, thus facilitating the production of live vaccine strains.

Protection against lethal lymphocytic choriomeningitis virus (LCMV) infection by immunization of mice with an influenza virus containing an LCMV epitope recognized by cytotoxic T lymphocytes

The reverse genetics system has made it possible to modify the influenza virus genome. By this method, we were able to assess influenza virus as a vaccine vector for protecting BALB/c mice against otherwise lethal lymphocytic choriomeningitis virus (LCMV) infection. A single dose of influenza virus [A/WSN/33 (H1N1)] bearing a cytotoxic T-lymphocyte-specific epitope of the LCMV nucleoprotein (residues 116 to 127) in the neuraminidase stalk protected mice against LCMV challenge for at least 4 months. The immunity was mediated by cytotoxic T lymphocytes and was haplotype specific, indicating that the observed protective response was solely a consequence of prior priming with the H-2d LCMV nucleoprotein epitope expressed in the recombinant influenza virus. We also found that as many as 58 amino acids could be inserted into the neuraminidase stalk without loss of viral function. These findings demonstrate the potential of influenza virus as a vaccine vector, with the neuraminidase stalk as a repository for foreign epitopes.

Antigenic and sequence analysis of H3 influenza virus haemagglutinins from pigs in Italy

To investigate the possible mechanism of maintenance of old human influenza A (H3N2) viruses in pigs, the haemagglutinins (HAs) of seven isolates from swine were studied by analysis of nucleotide and deduced primary amino acid sequences, as well as reactivity of the HA molecule to chicken antisera and monoclonal antibodies. The swine HAs were closely similar to the HA of the A/Victoria/3/75 human variant as regards antigenic and molecular characteristics. These findings are consistent with the hypothesis that the swine HA genes were transmitted from an early human H3 virus to pigs, where they survived with limited mutations over a period of 5 years. The sequence data were also compared with swine H3 sequences to investigate genetic relationships between the H3 genes from swine viruses isolated in different geographical areas. An evolutionary tree, constructed from the nucleotide sequences of viruses isolated from pigs in China and in Italy, illustrated that, depending on the country of their isolation, the HA genes of swine influenza A (H3N2) viruses have different origins, e.g. human and avian, and evolved independently in different lineages. The study provides direct support for the hypothesis that pigs might serve as a 'mixing vessel' for the generation of pandemic strains of human influenza viruses.

Mutations in the cytoplasmic tail of influenza A virus neuraminidase affect incorporation into virions

The significance of the conserved cytoplasmic tail sequence of influenza A virus neuraminidase (NA) was analyzed by the recently developed reverse genetics technique (W. Luytjes, M. Krystal, M. Enami, J. D. Parvin, and P. Palese, Cell 59:1107-1113, 1989). A chimeric influenza virus A/WSN/33 NA containing the influenza B virus cytoplasmic tail rescued influenza A virus infectivity. The transfectant virus had less NA incorporated into virions than A/WSN/33, indicating that the cytoplasmic tail of influenza virus NA plays a role in incorporation of NA into virions. However, these results also suggest that the influenza A virus and influenza B virus cytoplasmic tail sequences share common features that lead to the production of infectious virus. Transfectant virus was obtained with all cytoplasmic tail mutants generated by site-directed mutagenesis of the influenza A virus tail, except for the mutant resulting from substitution of the conserved proline residue, presumably because of its contribution to the secondary structure of the tail. No virus was rescued when the cytoplasmic tail was deleted, indicating that the cytoplasmic tail is essential for production of the virus. The virulence of the transfectant viruses in mice was directly proportional to the amount of NA incorporated. The importance of the NA cytoplasmic tail in virus assembly and virulence has implications for use in developing antiviral strategies.

Concurrent antigenic analysis of recent epidemic influenza A and B viruses and quantitation of antibodies in population serosurveys in Italy

Laboratory investigations of virus isolation and serum antibodies in a Mediterranean country (Italy) demonstrated that influenza A and B viruses, and often both, circulated every winter in Italy. The winter 1987/88 was characterized by a low level of influenza activity, as shown by the limited number (47) of influenza virus isolates, the majority of which (61%) belonged to the influenza B type. In contrast, the 1988/89 influenza season was exclusively associated with the circulation of influenza type A viruses. The A(H1H1) subtype was largely predominant (97%), as compared to the low incidence of the A(H3N2) subtype (3%). During the 1989/90 winter a co-circulation of A and B influenza viruses was observed, A(H3N2) strains being responsible for 96% of the virologically confirmed cases. Antigenic analysis of the virus isolates showed some antigenic variation in influenza A viruses of both H1N1 and H3N2 subtypes, whilst antigenic stability was found among the influenza B virus isolates. Overall, the above virological findings correlate with the data concerning the pattern of influenza virus circulation in Northern Europe and the UK during the three years surveyed. The results of serum antibody surveys conducted in each post-epidemic period are also reported.

Genetic reassortment between avian and human influenza A viruses in Italian pigs

Pandemic strains of influenza A virus arise by genetic reassortment between avian and human viruses. To examine the possibility that pigs serve as "mixing vessels" for such reassortment events (Scholtissek et al., Virology 147, 287-294, 1985), we phylogenetically analyzed the internal protein genes of classic H1N1, avian-like H1N1, and human-like H3N2 viruses circulating among Italian pigs. The results show that human-like H3N2 strains isolated from 1985 to 1989 contained the internal protein genes of avian-like H1N1 viruses, whereas those isolated in 1977 and 1983 did not. Thus, at some time between 1983 and 1985, genetic reassortment took place between avian- and human-like viruses in Italian pigs. This study provides the first evidence supporting genetic reassortment between human and avian viruses in a natural swine environment.

Biologic importance of neuraminidase stalk length in influenza A virus

To investigate the biologic importance of the neuraminidase (NA) stalk of influenza A virus, we generated mutant viruses of A/WSN/33 (H1N1) with stalks of various lengths (0 to 52 amino acids), by using the recently developed reverse genetics system. These mutant viruses, including one that lacked the entire stalk, replicated in tissue culture to the level of the parent virus, whose NA stalk contains 24 amino acid residues. In eggs, however, the length of the stalk was correlated with the efficiency of virus replication: the longer the stalk, the better the replication. This finding indicates that the length of the NA stalk affects the host range of influenza A viruses. The NA stalkless mutant was highly attenuated in mice; none of the animals died even after intranasal inoculation of 10(6) PFU of the virus (the dose of the parent virus required to kill 50% of mice was 10(2.5) PFU). Moreover, the stalkless mutant replicated only in the respiratory organs, whereas the parent virus caused systemic infection in mice. Thus, attenuation of the virus with the deletion of the entire NA stalk raises the possibility of its use as live vaccines.

Influenza--a model of an emerging virus disease

Influenza A viruses continue to emerge from the aquatic avian reservoir and cause pandemics. Phylogenetic analysis of the nucleotide sequence of all eight influenza A virus RNA segments indicate that all of the influenza viruses in mammalian hosts originate from the avian gene pool. In contrast to the rapid progressive changes in both the nucleotide and amino acid sequences of mammalian virus gene lineages, avian virus genes show far less variation and, in most cases, appear to be in evolutionary stasis. There are periodic exchanges of influenza virus genes or whole viruses between species giving rise to pandemics of diseases in humans, lower animals and birds. The periodic emergence of influenza viruses in mammalian species has been illustrated by the appearance of a new influenza virus in horses in northern China in 1989. Phylogenetic analysis of classical H1N1, avian-like H1N1 and human H3N2 viruses circulating in Italian pigs reveals that genetic reassortment is taking place between avian- and human-like viruses in the European pig population. These studies provide evidence supporting the possibility that pigs serve as a mixing vessel for reassortment between influenza viruses in mammalian and avian hosts and raise the question of whether the next pandemic of influenza will emerge in Europe!

Attenuation of influenza A virus by insertion of a foreign epitope into the neuraminidase

As the initial step in generating a live attenuated influenza A vaccine, we attempted to substitute an unrelated amino acid sequence (FLAG) for a portion of the neuraminidase (NA) molecule in influenza virus A/WSN/33 (H1N1), using a recently developed technique (reverse genetics [W. Luytjes, M. Krystal, M. Enami, J. D. Parvin, and P. Palese, Cell 59:1107-1113, 1989]). This technique allowed us to rescue the NA molecules containing the FLAG sequence (Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys) at the bottom portion of the boxlike head of the molecule immediately above the stalk region (amino acid residues 63 to 70 [WSN NA numbering]). An anti-FLAG monoclonal antibody immunoprecipitated the NA molecules with the FLAG sequence, demonstrating that the foreign epitope was exposed on the virion surface. The dose of FLAG-containing transfectant virus required to kill 50% of mice was 100-fold higher than the required dose of parent virus. The FLAG sequence was stably maintained in the NA molecule during passage of the virus in tissue culture and in mice. These findings demonstrate that live influenza A vaccine strains with stable attenuating mutations in the coding region of the viral genes can be generated by reverse genetics.

Immunization of elderly volunteers with the 1988-89 inactivated whole influenza vaccine: assessment of antibody responses by haemagglutination inhibition and single radial haemolysis tests

The immunogenicity of inactivated whole trivalent influenza vaccines (A/Taiwan/1/86 (H1N1), A/Sichuan/2/87 (H3N2), and B ijing/1/87) recommended for the 1988-89 winter season was evaluated in 236 elderly (mean age 71 years) high risk volunteers. An overall significant increase in the number of subjects with protective haemagglutination inhibiting (HI) antibodies (titer > 1:40) against vaccine components was observed after vaccination. Nevertheless, a percentage of individuals (ranging from 56% to 62%) remained without protective antibodies and the number of people showing a positive response was limited (from 32% to 41%). By the comparative analysis of the results obtained examining the presence of protective levels of antibody in the sera from 91 volunteers using HI versus the single radial haemolysis (SRH) test, we obtained evidence for a higher sensitivity of SRH technique especially against B antigen.

Detection of two antigenic subpopulations of A(H1N1) influenza viruses from pigs: antigenic drift or interspecies transmission?

Serological analysis of a group of 63 influenza H1N1 viruses isolated from pigs in Italy in the period 1976-1988 revealed the presence of two distinct antigenic subpopulations: some viruses possessed a haemagglutinin indistinguishable from that of viruses typically associated with pigs, i.e., A/New Jersey/8/76 (H1N1), whereas others showed a close antigenic relatedness with the haemagglutinin of avian-like H1 viruses. These findings represent further evidence that influenza A viruses from avian species may be transmitted to mammals. The surface and internal proteins of some of these viruses were also analyzed biochemically to evaluate the molecular relatedness among viruses circulating in non-human hosts.