Allergic Asthma Protects from H1N1 Influenza Virus and Streptococcus Pneumoniae

Pre-existing allergic asthma protects from severe morbidity from influenza A virus (IAV) and Streptococcus pneumoniae (Spn) co-infection because of extensive alterations in the respiratory tract including immunological and microbiological differences.

This Le Bonheur research, published in Scientific Reports, was prompted by the results from the 2009 swine flu pandemic during which asthmatics had less severe outcomes of influenza including reduced bacterial pneumonia and ICU admittance as compared to non-asthmatics.

“Asthma is a complicated syndrome that develops through intricate gene and environment interaction,” said Le Bonheur Researcher Amali Samarasinghe, PhD. “Our study aimed to understand the possible mechanisms at play in asthmatics during respiratory infections to determine how each asthmatic may respond.”

Researchers developed a mouse model of asthma, influenza and pneumococcal pneumonia in order to study host-pathogen interactions in live tissue, which is unable to be observed in humans.

The results of the study revealed several ways in which allergic airways differ from non-allergic during co-infection of IAV and Spn including:

1. The inflammation of allergic airways delayed or protected against severe disease from co-infection.
2. Allergic airways had a more diverse immune cell signature during co-infection.
3. Antibiotic treatment impeded protection from infection- induced morbidity in allergic
4. Lung mucosal microbiome was more diverse in allergic airways, and antibiotic-induced dysbiosis rendered the allergic mice susceptible to severe disease associated with co-infection.

“Underlying conditions present unique challenges and opportunities for invading pathogens,” said Samarasinghe. “The extensive alterations in the respiratory tract during allergic asthma encompass both immunological and microbiological differences that can have a profound impact on susceptibility to infection.”

The results show that asthmatics have a distinct microbial signature that may contribute to the protective capacity of asthma during IAV and Spn co-infection. Any antibiotics

should be prescribed with caution especially in patients with underlying chronic conditions.

This study was conducted in collaboration with St. Jude Children’s Research Hospital researchers Jason Rosch, PhD, Ti- Cheng Chang, PhD, and Peter Vogel, DVM, PhD.

View the full text article at https://www.nature.com/articles/s41598-019-55712-8#Abs1.