Pathological examination of lung tissues in influenza a virus-infected mice

Oral co-administration of Lactiplantibacillus plantarum 16 and Lacticaseibacillus rhamnosus P118 improves host defense against influenza A virus infection

Influenza is an important zoonotic disease that persistently threatens global public health. While it is widely acknowledged that probiotics can modulate the host response to protect the host against infectious disease, the prophylactic efficacy on respiratory viral infection and the detailed mechanism remains elusive. Lactobacillus, the most commonly used probiotic widely applied in food production, has garnered significant attention. In our study utilizing both C57BL/6 and BALB/c mouse models, we explored the protective effect against two strains of influenza virus, A/Mink/China/01/2014(H9N2) and A/California/04/2009(H1N1), through the administration of Lactiplantibacillus plantarum strain 16 (L. plantarum 16) and Lacticaseibacillus rhamnosus strain P118 (L. rhamnosus P118), aiming to identify robust probiotic strains with antiviral properties. Our findings indicate that administering L. plantarum 16 or L. rhamnosus P118 alone does not provide sufficient protection against influenza. However, the co-administration of L. plantarum 16 and L. rhamnosus P118 dramatically reduces viral titers in the respiratory tract and lung, thereby markedly alleviating the clinical symptoms, improving prognosis, and reducing mortality. The mechanisms underlying this effect involve the modulation of host gut microbiota and metabolism through the co-administration of L. plantarum 16 and L. rhamnosus P118, resulting in enrichment of Firmicutes and enhancement of phenylalanine-related metabolism, ultimately leading to an augmentation of the antiviral immune response. Notably, we identified that the circulating metabolic molecule 2-Hydroxycinnamic acid plays a significant role in combating influenza. Our data suggest the potential utility of L. plantarum 16 and L. rhamnosus P118 two-bacterium or 2-Hydroxycinnamic acid in preventing influenza.IMPORTANCEVaccination represents the most optimal strategy to control influenza. Nevertheless, influenza viruses constantly evolve due to antigenic drift and shift, leading to the need for regular updates on influenza vaccines. Additionally, vaccination failure poses significant challenges to influenza prevention. Therefore, it is essential and beneficial to identify novel or universal antiviral measures to protect against influenza. While cumulative data suggest that probiotics offer protection against infectious diseases, the specific mechanisms, such as the effective metabolites or components, remain largely unknown. Our research discovered the capacity of combinational two-bacterium Lactiplantibacillus plantarum 16 and Lacticaseibacillus rhamnosus P118 to fight against influenza infection in a mouse model. The protection may occur through modulating the host's gut microbiota and metabolism, further influencing the host's antiviral immune response. Notably, we have identified a novel metabolic molecule, 2-Hydroxycinnamic acid, capable of enhancing antiviral response and restricting viral replication in vivo.

Virus-Induced T Cell-Mediated Heterologous Immunity and Vaccine Development

Heterologous immunity (H.I.) is a consequence of an encounter with a specific antigen, which can alter the subsequent immune response to a different antigen. This can happen at the innate immune system level—often called trained immunity or innate immune memory—and/or at the adaptive immune system level involving T memory cells and antibodies. Viruses may also induce T cell-mediated H.I., which can confer protection or drive immunopathology against other virus subtypes, related or unrelated viruses, other pathogens, auto- or allo-antigens. It is important to understand the underlying mechanisms for the development of antiviral “universal” vaccines and broader T cell responses rather than just subtype-specific antibody responses as in the case of influenza. Furthermore, knowledge about determinants of vaccine-mediated H.I. may inform public health policies and provide suggestions for repurposing existing vaccines. Here, we introduce H.I. and provide an overview of evidence on virus- and antiviral vaccine-induced T cell-mediated cross-reactive responses. We also discuss the factors influencing final clinical outcome of virus-mediated H.I. as well as non-specific beneficial effects of live attenuated antiviral vaccines such as measles and vaccinia. Available epidemiological and mechanistic data have implications both for the development of new vaccines and for personalized vaccinology, which are presented. Finally, we formulate future research priorities and opportunities.

Pathology of Equine Influenza virus (H3N8) in Murine Model

Equine influenza viruses (EIV)—H3N8 continue to circulate in equine population throughout the world. They evolve by the process of antigenic drift that leads to substantial change in the antigenicity of the virus, thereby necessitating substitution of virus strain in the vaccines. This requires frequent testing of the new vaccines in the in vivo system; however, lack of an appropriate laboratory animal challenge model for testing protective efficacy of equine influenza vaccine candidates hinders the screening of new vaccines and other therapeutic approaches. In the present investigation, BALB/c mouse were explored for suitability for conducting pathogenecity studies for EIV. The BALB/c mice were inoculated intranasally @ 2×10^6.24 EID₅₀ with EIV (H3N8) belonging to Clade 2 of Florida sublineage and monitored for setting up of infection and associated parameters. All mice inoculated with EIV exhibited clinical signs viz. loss in body weights, lethargy, dyspnea, etc, between 3 and 5 days which commensurate with lesions observed in the respiratory tract including rhinitis, tracheitis, bronchitis, bronchiolitis, alveolitis and diffuse interstitial pneumonia. Transmission electron microscopy, immunohistochemistry, virus quantification through titration and qRT-PCR demonstrated active viral infection in the upper and lower respiratory tract. Serology revealed rise in serum lactate dehydrogenase levels along with sero-conversion. The pattern of disease progression, pathological lesions and virus recovery from nasal washings and lungs in the present investigations in mice were comparable to natural and experimental EIV infection in equines. The findings establish BALB/c mice as small animal model for studying EIV (H3N8) infection and will have immense potential for dissecting viral pathogenesis, vaccine efficacy studies, preliminary screening of vaccine candidates and antiviral therapeutics against EIV.

Impaired heterologous immunity in aged ferrets during sequential influenza A H1N1 infection

The major burden of influenza morbidity resides within the elderly population. The challenge managing influenza-associated illness in the elderly is the decline of immune function, where mechanisms leading to immunological senescence have not been elucidated. To better represent the immune environment, we investigated clinical morbidity and immune function during sequential homologous and heterologous H1N1 influenza infection in an aged ferret model. Our findings demonstrated experimentally that aged ferrets had significant morbidity during monosubtypic heterologous 2° challenge with significant weight loss and respiratory symptoms. Furthermore, increased clinical morbidity was associated with slower and shorter hemagglutinin antibody generation and attenuated type 1 T-cell gene responses in peripheral blood. These results revealed dampened immune activation during sequential influenza infection in aged ferrets. With the presence of an aged model, dissecting clinical morbidity, viral dynamics and immune response during influenza infection will aid the development of future prophylactics such as age specific influenza vaccines.