Saliva as a useful tool for evaluating upper mucosal antibody response to influenza

Mucosal immunity plays a crucial role in controlling upper respiratory infections, including influenza. We established a quantitative ELISA to measure the amount of influenza virus-specific salivery IgA (sIgA) and salivary IgG (sIgG) antibodies using a standard antibody broadly reactive to the influenza A virus. We then analyzed saliva and serum samples from seven individuals infected with the A(H1N1)pdm09 influenza virus during the 2019-2020 flu seasons. We detected an early (6-10 days post-infection) increase of sIgA in five of the seven samples and a later (3-5 weeks) increase of sIgG in six of the seven saliva samples. Although the conventional parenteral influenza vaccine did not induce IgA production in saliva, vaccinated individuals with a history of influenza infection had higher basal levels of sIgA than those without a history. Interestingly, we observed sIgA and sIgG in an asymptomatic individual who had close contact with two influenza cases. Both early mucosal sIgA secretion and late systemically induced sIgG in the mucosal surface may protect against virus infection. Despite the small sample size, our results indicate that the saliva test system can be useful for analyzing upper mucosal immunity in influenza.

Automated summary

Mucosal immunity is crucial for controlling upper respiratory infections, including influenza. A study established a quantitative ELISA method to measure the levels of influenza virus-specific salivary IgA (sIgA) and salivary IgG (sIgG) antibodies. The study analyzed samples from individuals infected with the A(H1N1)pdm09 influenza virus and found an early increase of sIgA and a later increase of sIgG in saliva. Interestingly, individuals with a history of influenza infection and vaccination had higher levels of sIgA in their saliva. The study suggests that the saliva test system is useful for analyzing upper mucosal immunity in influenza, despite the small sample size.