Study Explores Role of Nasal Bacteria, Provides Clues to Develop Better Flu and COVID-19 Vaccines

While the gut microbiota plays a critical role in inducing adaptive immune responses to influenza virus infection, the role of nasal bacteria in inducing virus-specific adaptive immunity is less clear. New research published this week in mBio, an open access journal of the American Society for Microbiology, explores the role of nasal bacteria and provides clues to develop better intranasal influenza and COVID-19 vaccines.

Our study shows that the integrity and quantities of nasal bacteria can be critical for an effective intranasal vaccine. We have shown that the intranasal vaccine combined with oral bacteria protects against influenza virus and SARS-CoV-2 infection. “

Takeshi Ichinohe, Ph.D., Study Principal Investigator, Associate Professor, Division of Viral Infections, Department of Infectious Disease Control, International Center for Infectious Disease Research, Institute of Medical Sciences, University of Tokyo, Minato -ku, Tokyo, Japan

In the new study, to determine the effects of nasal bacteria in inducing mucosal immune responses to influenza virus infection, Dr. Ichniohe and colleagues treated mice intranasally with an antibiotic cocktail to kill nasal bacteria before influenza virus infection.

The researchers found that disruption of nasal bacteria by antibiotics before infection with the influenza virus enhanced the virus-specific antibody responses. “We found that intranasal application of antibiotics (to kill nasal bacteria) could release molecular patterns associated with bacterial pathogens (PAMPs), which are bacterial components that stimulate innate immunity that act as mucosal adjuvants. for the response of specific antibodies to the influenza virus, “said Dr. Ichniohe.

Innate immunity, which is not specific to a particular pathogen, is the first line of defense against non-autonomous pathogens such as bacteria and viruses. The main goal of the innate immune response is to immediately prevent the spread and movement of foreign pathogens throughout the body. Innate immune responses play an essential role in inducing pathogen-specific adaptive immune responses. Adjuvants are substances that increase or modulate the immune response to a vaccine and stimulate the innate immune system.

The researchers also found that while the upper respiratory tract contained commensal bacteria, the relative amounts of cultivable commensal bacteria in the surface of the nasal mucosa were significantly lower than in the oral cavity. Researchers tested whether intranasal supplementation of cultured oral bacteria improves antibody responses to the vaccine given intranasally and found that oral bacteria combined with the intranasal vaccine increased antibody responses to the vaccine given intranasally.

Dr Ichniohe said the results provide clues for developing better intranasal vaccines. “We are keen to develop effective intranasal influenza and COVID-19 vaccines in the near future,” said Dr Ichniohe.