Will the next human influenza pandemic be caused by the virus of the avian flu A/H5N1? Arguments pro and counter

The protective effect of a combination of human intracellular and extracellular antibodies against the highly pathogenic avian influenza H5N1 virus

Background

The highly pathogenic avian influenza H5N1 virus poses a serious threat to humans. Due to its antiviral activity, antibody-based therapy is one of the possible effective countermeasures. Here, a combination of intracellular and extracellular human antibodies was investigated and showed an improved protective effect.

Methods

The scFv4F5-based intracellular antibody vectors and IgG1 extracellular antibody were constructed and expressed, respectively, and the sensitivity, specificity, and affinity of these antibodies were determined in vitro. In vivo, the protective effect of IgG1 and the combination of antibodies were tested respectively. Furthermore, the dynamics of viral replication, the related cytokines and apoptosis-related proteins were detected.

Results

In vitro, the expressed intracellular antibody inhibited H5N1 virus propagation and the IgG1 exhibited high specificity, sensitivity, and affinity against the H5N1 virus. In vivo, the extracellular antibody could inhibit viral propagation in a dose-dependent manner. The protective effect of IgG1 was good in a mouse model, and the survival was 100% at a dose of 15 mg/kg under infection with 100 TCID₅₀ virus. When the intracellular antibody was pre-transfected in combination with IgG1, it had a better protective effect. The survival was 16.67% under treatment with IgG1 alone and up to 83.33% under treatment with the combination of antibodies when challenge of 500 TCID ₅₀ virus. Furthermore, the levels of cytokines IFN-γ, IL-6, IL-10 and some apoptosis-related proteins increased.

Conclusions

This antibody combination technique could be used as an appropriate and powerful alternative to antiviral therapy.

Computational Prediction of the Epitopes of HA1 Protein of Influenza Viruses to its Neutralizing Antibodies

In this work, we have used a new method to predict the epitopes of HA1 protein of influenza virus to several antibodies HC19, CR9114, BH151 and 4F5. While our results reproduced the binding epitopes of H3N2 or H5N1 for the neutralizing antibodies HC19, CR9114, and BH151 as revealed from the available crystal structures, additional epitopes for these antibodies were also suggested. Moreover, the predicted epitopes of H5N1 HA1 for the newly developed antibody 4F5 are located at the receptor binding domain, while previous study identified a region 76-WLLGNP-81 as the epitope. The possibility of antibody recognition of influenza virus via different mechanism by binding to different epitopes of an antigen is also discussed.

Human 4F5 single-chain Fv antibody recognizing a conserved HA1 epitope has broad neutralizing potency against H5N1 influenza A viruses of different clades

Influenza A viruses present a significant threat to public health worldwide. High-affinity human scFv antibodies against a conserved epitope can potentially provide immunity to diverse viruses and protect against future pandemic viruses. A library of phage-displayed human scFv containing 6.0×10(8) members was generated from lymphocytes of H5N1 virus vaccinated individuals. Using the recombinant H5N1 virus hemagglutinin ectodomain (HA1), 4F5 scFv was identified with neutralizing activity against both clade 2 and 9 H5N1 viruses. In embryonated chicken eggs, the antiviral activity of 4F5 scFv conferred a 100% survival rate and at least a 62.5% survival rate against different clades of H5N1 viruses by pre-treatment and post-treatment, respectively. 4F5 scFv belongs to the VH-3-43 family according to the IMGT database, and a peptide (76)WLLGNP(81) containing half of an α-helix in HA1 was identified as the binding pocket. The conserved binding epitope of this novel broadly neutralizing scFv may become key in the design and implementation of vaccines or RNA interference against H5N1 viruses.

Recent publications in medical microbiology and immunology: a retrospective

A look back is done to some clinical and basic research activities recently published in medical microbiology and immunology. The review covers clinical experiences and in vitro experiments to understand the emergency, pathogenicity, epidemic spread, and vaccine-based prevention of avian and swine-origin flu. Some new developments and concepts in diagnosis, (molecular) epidemiology, and therapy of AIDS, viral hepatitis C, and herpesvirus-associated diseases are outlined. Regulation of immune system has been discussed in a special issue 2010 including some aspects of CNS affections (measles). Mycobacterial infection and its prevention by modern recombinant vaccines have reached new interest, as well as new concepts of vaccination and prophylaxis against several other bacteria. Adaptation to host niches enables immune escape (example brucella) and determines virulence (example N. meningitidis). Chlamydia pneumoniae, previously considered to trigger atherosclerosis, is hypothetically associated to Alzheimer disease, while CMV, another putative trigger of atherosclerosis, gains evidence of oncomodulation in CNS tumor diseases. In terms of globalization, exotic virus infections are increasingly imported from southern countries.

The threat of avian influenza A (H5N1). Part I: epidemiologic concerns and virulence determinants

Among emerging and re-emerging infectious diseases, influenza constitutes one of the major threats to mankind. In this review series epidemiologic, virologic and pathologic concerns raised by infections of humans with avian influenza virus A/H5N1 are discussed. This first part concentrates on epidemiologic concerns and virulence determinants. H5N1 spread over the world and caused a series of fowl pest outbreaks. Significant human-to-human transmissions have not been observed yet. Mutations that make the virus more compatible with human-to-human transmission may occur at any time. Nevertheless, no one can currently predict with certainty whether H5N1 will become a human pandemic virus.