Recalling the #Future: #Immunological #Memory Toward Unpredictable #Influenza Viruses (Front Immunol., abstract)

[Source: US National Library of Medicine, full page: (LINK). Abstract, edited.]

Front Immunol. 2019 Jul 2;10:1400. doi: 10.3389/fimmu.2019.01400. eCollection 2019.

Recalling the Future: Immunological Memory Toward Unpredictable Influenza Viruses.

Auladell M1, Jia X1, Hensen L1, Chua B1,2, Fox A3, Nguyen THO1, Doherty PC1,4, Kedzierska K1.

Author information: 1 Department of Microbiology and Immunology, Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, VIC, Australia. 2 Research Center for Zoonosis Control, Hokkaido University, Sapporo, Japan. 3 WHO Collaborating Centre for Reference and Research on Influenza, Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia. 4 Department of Immunology, St. Jude Children’s Research Hospital, Memphis, TN, United States.



Persistent and durable immunological memory forms the basis of any successful vaccination protocol. Generation of pre-existing memory B cell and T cell pools is thus the key for maintaining protective immunity to seasonal, pandemic and avian influenza viruses. Long-lived antibody secreting cells (ASCs) are responsible for maintaining antibody levels in peripheral blood. Generated with CD4+ T help after naïve B cell precursors encounter their cognate antigen, the linked processes of differentiation (including Ig class switching) and proliferation also give rise to memory B cells, which then can change rapidly to ASC status after subsequent influenza encounters. Given that influenza viruses evolve rapidly as a consequence of antibody-driven mutational change (antigenic drift), the current influenza vaccines need to be reformulated frequently and annual vaccination is recommended. Without that process of regular renewal, they provide little protection against “drifted” (particularly H3N2) variants and are mainly ineffective when a novel pandemic (2009 A/H1N1 “swine” flu) strain suddenly emerges. Such limitation of antibody-mediated protection might be circumvented, at least in part, by adding a novel vaccine component that promotes cross-reactive CD8+ T cells specific for conserved viral peptides, presented by widely distributed HLA types. Such “memory” cytotoxic T lymphocytes (CTLs) can rapidly be recalled to CTL effector status. Here, we review how B cells and follicular T cells are elicited following influenza vaccination and how they survive into a long-term memory. We describe how CD8+ CTL memory is established following influenza virus infection, and how a robust CTL recall response can lead to more rapid virus elimination by destroying virus-infected cells, and recovery. Exploiting long-term, cross-reactive CTL against the continuously evolving and unpredictable influenza viruses provides a possible mechanism for preventing a disastrous pandemic comparable to the 1918-1919 H1N1 “Spanish flu,” which killed more than 50 million people worldwide.

KEYWORDS: B cells; T cells; immunological memory; influenza; vaccine

PMID: 31312199 PMCID: PMC6614380 DOI: 10.3389/fimmu.2019.01400

Keywords: Influenza A; Seasonal Influenza; Pandemic Influenza; Vaccines; Immunology.



#Treatment-Emergent #Influenza Variant Viruses With Reduced #Baloxavir Susceptibility: Impact on #Clinical and Virologic #Outcomes in Uncomplicated Influenza (J Infect Dis., abstract)

[Source: Journal of Infectious Diseases, full page: (LINK). Abstract, edited.]

Treatment-Emergent Influenza Variant Viruses With Reduced Baloxavir Susceptibility: Impact on Clinical and Virologic Outcomes in Uncomplicated Influenza

Takeki Uehara, Frederick G Hayden, Keiko Kawaguchi, Shinya Omoto, Aeron C Hurt, Menno D De Jong, Nobuo Hirotsu, Norio Sugaya, Nelson Lee, Keiko Baba, Takao Shishido, Kenji Tsuchiya, Simon Portsmouth, Hiroshi Kida

The Journal of Infectious Diseases, jiz244,

Published: 16 July 2019




Single-dose baloxavir rapidly reduces influenza virus titers and symptoms in patients with uncomplicated influenza, but viruses with reduced in vitro susceptibility due to amino acid substitutions at position 38 of polymerase acidic protein (PA/I38X) sometimes emerge.


We evaluated the kinetics, risk factors, and effects on clinical and virologic outcomes of emergence of PA/I38X-substituted viruses.


Viruses containing PA/I38X substitutions were identified 3–9 days after baloxavir treatment in 9.7% (36/370) of patients, of whom 85.3% had transient virus titer rises. Median time to sustained cessation of infectious virus detection was 192, 48, and 96 hours in the baloxavir recipients with PA/I38X-substituted viruses, without PA/I38X-substituted viruses, and placebo recipients, respectively. The corresponding median times to alleviation of symptoms were 63.1, 51.0, and 80.2 hours, respectively. After day 5, symptom increases occurred in 11.5%, 8.0%, and 13.0%, respectively, and in 8.9% of oseltamivir recipients. Variant virus emergence was associated with lower baseline neutralizing antibody titers.


The emergence of viruses with PA/I38X substitutions following baloxavir treatment was associated with transient rises in infectious virus titers, prolongation of virus detectability, initial delay in symptom alleviation, and uncommonly with symptom rebound. The potential transmissibility of PA/I38X-substituted viruses requires careful study.

Clinical Trial Registration NCT02954354.

antiviral susceptibility, baloxavir marboxil, cap-dependent endonuclease, influenza, polymerase acidic protein

Issue Section: Major Article

Keywords: Influenza A; Antivirals; Drugs Resistance; Baloxavir Marboxil.


#Azithromycin, a 15-membered #macrolide #antibiotic, inhibits #influenza A #H1N1pdm09 virus #infection by interfering with virus internalization process (J Antibit (Tokyo), abstract)

[Source: US National Library of Medicine, full page: (LINK). Abstract, edited.]

J Antibiot (Tokyo). 2019 Jul 12. doi: 10.1038/s41429-019-0204-x. [Epub ahead of print]

Azithromycin, a 15-membered macrolide antibiotic, inhibits influenza A(H1N1)pdm09 virus infection by interfering with virus internalization process.

Tran DH1,2, Sugamata R1,2,3, Hirose T4, Suzuki S1,2,3, Noguchi Y4, Sugawara A4,5, Ito F2, Yamamoto T2, Kawachi S2,3, Akagawa KS4, Ōmura S4, Sunazuka T4, Ito N6, Mimaki M6, Suzuki K7,8,9.

Author information: 1 Department of Health Protection, Graduate School of Medicine, Teikyo University, Kaga 2-11-1, Itabashi-ku, Tokyo, 173-8605, Japan. 2 Asia International Institute of Infectious Disease Control (ADC), Teikyo University, Kaga 2-11-1, Itabashi-ku, Tokyo, 173-8605, Japan. 3 General Medical Education and Research Center (G-MEC), Teikyo University, Kaga 2-11-1, Itabashi-ku, Tokyo, 173-8605, Japan. 4 Kitasato Institute for Life Sciences and Graduate School of Infection Control Sciences, Kitasato University, Shirokane 5-9-1, Minato-ku, Tokyo, 108-8641, Japan. 5 Graduate School of Pharmaceutical Sciences, Tohoku University, Aza-Aoba 6-3, Aramaki, Aoba-ku, Sendai, 980-8578, Japan. 6 The Pediatric Department, Teikyo Hospital University, Kaga 2-11-1, Itabashi-ku, Tokyo, 173-8605, Japan. 7 Department of Health Protection, Graduate School of Medicine, Teikyo University, Kaga 2-11-1, Itabashi-ku, Tokyo, 173-8605, Japan. 8 Asia International Institute of Infectious Disease Control (ADC), Teikyo University, Kaga 2-11-1, Itabashi-ku, Tokyo, 173-8605, Japan. 9 General Medical Education and Research Center (G-MEC), Teikyo University, Kaga 2-11-1, Itabashi-ku, Tokyo, 173-8605, Japan.



The pandemic influenza 2009 (A(H1N1)pdm09) virus currently causes seasonal and annual epidemic outbreaks. The widespread use of anti-influenza drugs such as neuraminidase and matrix protein 2 (M2) channel inhibitors has resulted in the emergence of drug-resistant influenza viruses. In this study, we aimed to determine the anti-influenza A(H1N1)pdm09 virus activity of azithromycin, a re-positioned macrolide antibiotic with potential as a new anti-influenza candidate, and to elucidate its underlying mechanisms of action. We performed in vitro and in vivo studies to address this. Our in vitro approaches indicated that progeny virus replication was remarkably inhibited by treating viruses with azithromycin before infection; however, azithromycin administration after infection did not affect this process. We next investigated the steps inhibited by azithromycin during virus invasion. Azithromycin did not affect attachment of viruses onto the cell surface, but blocked internalization into host cells during the early phase of infection. We further demonstrated that azithromycin targeted newly budded progeny virus from the host cells and inactivated their endocytic activity. This unique inhibitory mechanism has not been observed for other anti-influenza drugs, indicating the potential activity of azithromycin before and after influenza virus infection. Considering these in vitro observations, we administered azithromycin intranasally to mice infected with A(H1N1)pdm09 virus. Single intranasal azithromycin treatment successfully reduced viral load in the lungs and relieved hypothermia, which was induced by infection. Our findings indicate the possibility that azithromycin could be an effective macrolide for the treatment of human influenza.

PMID:  31300721  DOI: 10.1038/s41429-019-0204-x

Keywords: Antibiotics; Azithromycin; Influenza A; H1N1pdm09.


#ADE of #influenza #disease promoted by increase in #hemagglutinin stem flexibility and virus #fusion kinetics (Proc Natl Acad Sci USA, abstract)

[Source: Proceedings of the National Academy of Sciences of the United States of America, full page: (LINK). Abstract, edited.]

Antibody-dependent enhancement of influenza disease promoted by increase in hemagglutinin stem flexibility and virus fusion kinetics

Katie L. Winarski, Juanjie Tang, Laura Klenow, Jeehyun Lee, Elizabeth M. Coyle, Jody Manischewitz, Hannah L. Turner, Kazuyo Takeda, Andrew B. Ward, Hana Golding, and Surender Khurana

PNAS first published July 11, 2019 / DOI:

Edited by Robert G. Webster, St. Jude Children’s Research Hospital, Memphis, TN, and approved June 19, 2019 (received for review December 14, 2018)



Next-generation influenza vaccines and broadly neutralizing antibodies (bNAbs) are in clinical development. Some of these do not block virus–receptor interactions and thus are predicted to provide protection via alternative mechanisms at the postentry stage or use Fc-dependent mechanisms. Nonneutralizing antibodies have the potential to mediate enhancement of respiratory disease (ERD). Our study describes ADE with two different functional MAbs that destabilized HA stem domain, increased influenza virus fusion kinetics, and led to enhanced lung pathology and ERD in a dose-dependent manner in a mice model. This study underlines careful preclinical evaluation of next-generation influenza vaccines or antibody-based therapeutics that do not block influenza virus receptor binding.



Several next-generation (universal) influenza vaccines and broadly neutralizing antibodies (bNAbs) are in clinical development. Some of these mediate inhibitions of virus replication at the postentry stage or use Fc-dependent mechanisms. Nonneutralizing antibodies have the potential to mediate enhancement of viral infection or disease. In the current study, two monoclonal antibodies (MAbs) 72/8 and 69/1, enhanced respiratory disease (ERD) in mice following H3N2 virus challenge by demonstrating increased lung pathology and changes in lung cytokine/chemokine levels. MAb 78/2 caused changes in the lung viral loads in a dose-dependent manner. Both MAbs increased HA sensitivity to trypsin cleavage at a higher pH range, suggesting MAb-induced conformational changes. pHrodo-labeled virus particles’ entry and residence time in the endocytic compartment were tracked during infection of Madin-Darby canine kidney (MDCK) cells. Both MAbs reduced H3N2 virus residence time in the endocytic pathway, suggesting faster virus fusion kinetics. Structurally, 78/2 and 69/1 Fabs bound the globular head or base of the head domain of influenza hemagglutinin (HA), respectively, and induced destabilization of the HA stem domain. Together, this study describes Mab-induced destabilization of the influenza HA stem domain, faster kinetics of influenza virus fusion, and ERD in vivo. The in vivo animal model and in vitro assays described could augment preclinical safety evaluation of antibodies and next-generation influenza vaccines that generate antibodies which do not block influenza virus–receptor interaction.

universal – stem – influenza – antibody-dependent enhancement (ADE) – vaccine



1 K.L.W., J.T., and L.K. contributed equally to this work.

2 To whom correspondence may be addressed. Email:

Author contributions: S.K. designed research; K.L.W., J.T., L.K., J.L., E.M.C., J.M., H.L.T., K.T., A.B.W., and S.K. performed research; K.L.W., J.T., L.K., H.L.T., K.T., A.B.W., and S.K. analyzed data; and A.B.W., H.G., and S.K. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

This article contains supporting information online at

Published under the PNAS license.

Keywords: Influenza A; Monoclonal antibodies; Vaccines; Antibody Dependent Enhancement.


Serial Section Array Scanning Electron Microscopy Analysis of Cells from #Lung #Autopsy #Specimens Following #Fatal A/ #H1N1pdm09 #Influenza Virus #Infection (J Virol., abstract)

[Source: Journal of Virology, full page: (LINK). Abstract, edited.]

Serial Section Array Scanning Electron Microscopy Analysis of Cells from Lung Autopsy Specimens Following Fatal A/H1N1 2009 Pandemic Influenza Virus Infection

Michiyo Kataoka, Kinji Ishida, Katsutoshi Ogasawara, Takayuki Nozaki, Yoh-ichi Satoh, Tetsutaro Sata, Yuko Sato, Hideki Hasegawa, Noriko Nakajima

DOI: 10.1128/JVI.00644-19



A/H1N1 2009 pandemic influenza virus (A/H1N1/pdm09) was first identified as a novel pandemic influenza A virus (IAV) in 2009. Previously, we reported that many viral antigens were detected in type II alveolar epithelial cells (AEC-IIs) within autopsied lung tissue from a patient with A/H1N1/pdm09 pneumonia. It is important to identify the association between the virus and host cells to elucidate the pathogenesis of IAV pneumonia. To investigate the distribution of virus particles and morphological changes in host cells, the autopsied lung specimens from this patient were examined using transmission electron microscopy (TEM) and a novel scanning electron microscopy (SEM) method. We focused on AEC-IIs as viral antigen-positive cells, and on monocytes/macrophages (Ms/MΦs) and neutrophils (Neus) as innate immune cells. We identified virus particles and intranuclear dense tubules, which are associated with matrix 1 (M1) proteins from IAV. Large-scale two-dimensional observation was enabled by digitally ‘stitching’ together contiguous SEM images. A single whole cell analysis using a serial section array (SSA)-SEM identified virus particles in vesicles within the cytoplasm and/or around the cell surface of AEC-IIs, Ms/MΦs, and Neus; however, intranuclear dense tubules were found only in AEC-IIs. Computer-assisted processing of SSA-SEM images from each cell type enabled 3D modeling of the distribution of virus particles within an ACE-II, a M/MΦ, and a Neu.



Generally, it is difficult to observe IAV particles in post-mortem samples from patients with seasonal influenza. In fact, only a few viral antigens are detected in bronchial epithelial cells from autopsied lung sections. Previously, we detected many viral antigens in AEC-IIs from the lung. This was because the majority of A/H1N1/pdm09 in the lung tissue harbored an aspartic acid to glycine substitution at position 222 (D222G) of the hemagglutinin protein. A/H1N1/pdm09 harboring the D222G substitution has a receptor-binding preference for α-2,3-linked sialic acids expressed on human AECs and infects them in the same way as H5N1 and H7N9 avian IAVs. Here, we report the first successful observation of virus particles not only in AEC-IIs, but also in Ms/MΦs and Neus, using electron microscopy. The finding of a M/MΦ harboring numerous virus particles within vesicles and at the cell surface suggests that Ms/MΦs are involved in the pathogenesis of IAV primary pneumonia.

Copyright © 2019 Kataoka et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.

Keywords: Influenza A; Seasonal Influenza; Pandemic Influenza; Avian Influenza; H1N1pdm09; H5N1; H7N9; Viral pathogenesis.


Susceptibility of #Influenza A, B, C, and D Viruses to #Baloxavir (Emerg Infect Dis., abstract)

[Source: US Centers for Disease Control and Prevention (CDC), Emerging Infectious Diseases Journal, full page: (LINK). Abstract, edited.]

Volume 25, Number 10—October 2019 / Dispatch

Susceptibility of Influenza A, B, C, and D Viruses to Baloxavir

Vasiliy P. Mishin, Mira C. Patel, Anton Chesnokov, Juan De La Cruz, Ha T. Nguyen, Lori Lollis, Erin Hodges, Yunho Jang, John Barnes, Timothy Uyeki, Charles T. Davis, David E. Wentworth, and Larisa V. Gubareva

Author affiliations: Centers for Disease Control and Prevention, Atlanta, Georgia, USA (V.P. Mishin, M.C. Patel, A. Chesnokov, J. De La Cruz, H.T. Nguyen, L. Lollis, E. Hodges, Y. Jang, J. Barnes, T. Uyeki, C.T. Davis, D.E. Wentworth, L.V. Gubareva); Battelle Memorial Institute, Atlanta (M.C. Patel, J. De La Cruz, H.T. Nguyen, L. Lollis)



Baloxavir showed broad-spectrum in vitro replication inhibition of 4 types of influenza viruses (90% effective concentration range 1.2–98.3 nmol/L); susceptibility pattern was influenza A ˃ B ˃ C ˃ D. This drug also inhibited influenza A viruses of avian and swine origin, including viruses that have pandemic potential and those resistant to neuraminidase inhibitors.

Keywords: Antivirals; Drugs Resistance; Oseltamivir; Favipiravir; Baloxavir; Influenza A; Influenza B; Influenza C; Influenza D; H1N1pdm09; H3N2; H7N9.


The Establishment and #Validation of the #Human U937 Cell Line as a Cellular #Model to Screen #Immunomodulatory Agents Regulating #Cytokine Release Induced by #Influenza Virus #Infection (Virol Sin., abstract)

[Source: Virologica Sinica, full page: (LINK). Abstract, edited.]

The Establishment and Validation of the Human U937 Cell Line as a Cellular Model to Screen Immunomodulatory Agents Regulating Cytokine Release Induced by Influenza Virus Infection

Authors: Ge Liu, Si Chen, Ao Hu, Li Zhang, Wenyu Sun, Jungang Chen, Wei Tang, Haiwei Zhang, Chunlan Liu, Chang Ke, Xulin Chen

RESEARCH ARTICLE/ First Online: 08 July 2019



Severe influenza infections are often associated with the excessive induction of pro-inflammatory cytokines, which is also referred to as “cytokine storms”. Several studies have shown that cytokine storms are directly associated with influenza-induced fatal acute lung injury and acute respiratory distress syndrome. Due to the narrow administration window, current antiviral therapies are often inadequate. The efforts to use immunomodulatory agents alone or in combination with antiviral agents in the treatment of influenza in animal models have resulted in the achievement of protective effects accompanied with reduced cytokine production. Currently, there are no immunomodulatory drugs for influenza available for clinical use. Animal models, despite being ideal to study the anti-inflammatory responses to influenza virus infection, are very costly and time-consuming. Therefore, there is an urgent need to establish fast and economical screening methods using cell-based models to screen and develop novel immunomodulatory agents. In this study, we screened seven human cell lines and found that the human monocytic cell U937 supports the replication of different subtypes of influenza viruses as well as the production of the important pro-inflammatory cytokines and was selected to develop the cell-based model. The U937 cell model was validated by testing a panel of known antiviral and immunomodulatory agents and screening a drug library consisting of 1280 compounds comprised mostly of FDA-approved drugs. We demonstrated that the U937 cell model is robust and suitable for the high-throughput screening of immunomodulators and antivirals against influenza infection.

Keywords: Influenza – Immunomodulatory agent – U937 cell – CCL2 – CXCL10


Electronic supplementary material

The online version of this article ( contains supplementary material, which is available to authorized users.




We thank Dr. Ding Gao and Ms. Juan Min (Center for instrumental analysis and metrology, Wuhan Institute of Virology, CAS) and Professor Xuefang An (Center for the animal experiments) for technical support. This work was supported by the Important Hubei Science and Technology Innovation Plan 2015ACA062 (to Xulin Chen) and the Natural Science Foundation of Hubei Province (2018CFB244, to Jungang Chen).

Author Contributions

GL and XC designed the experiments. GL, SC, AH, LZ, WS, JC, WT, HZ, CL, and CK performed the experiments. WT, CL, and HZ contributed to the reagents. GL and XC wrote and finalized the manuscript.


Compliance with Ethical Standards

Conflict of interest

The authors declare that they have no conflict of interest.

Animal and Human Rights Statement

This article does not contain any studies with human or animal subjects performed by any of the authors.

Keywords: Influenza A; Immunomodulators.