Researchers at Monash Medical Centre in Australia recently published in the Journal of Immunology Research a review regarding the immune response in lungs against the bacterium nontypeable Haemophilus influenzae. The study is entitled “The Lung Immune Response to Nontypeable Haemophilus influenzae (Lung Immunity to NTHi)”.
Haemophilus influenzae is a bacterium that has been previously mistaken as the cause of influenza (the flu). It can cause a severe infection, mostly in infants and children younger than five years of age, which can be fatal or lead to lifelong disability. H. influenzae has been divided into two types of strains, typeable and nontypeable, based on the presence or absence of a polysaccharide capsule, respectively.
Nontypeable H. influenzae (NTHi) predominantly corresponds to respiratory mucosal pathogens, being present in the microbial community in the nasopharynx. When NTHi spreads into the lower respiratory tract, it becomes a respiratory pathogen and induces a strong inflammatory response. NTHi has been linked to several lung disorders including bronchiectasis, a respiratory condition characterized by a chronic inflammation that usually results from an infection that injures the walls of the airways, causing irreversible airway dilatation and scarring. In bronchiectasis, the airways slowly lose their ability to clear out mucus, so it accumulates in the lungs, creating ent prone to bacteria growth that can lead to severe lung infections. Sputum production, chronic cough and recurrent chest infections are signs of the disease.
In adults, NTHi is an important cause of pneumonia, especially in patients with chronic lung disease such as bronchiectasis. NTHi is in fact the main bacterium isolated in patients with bronchiectasis.
The authors believe that the lung host immunity is most likely a critical factor in the prevention of disease caused by NTHi; however, the link between host immunity and NTHi is still not well defined. The team emphasizes that in order to develop more effective therapies for treatment of disease caused by NTHi, the host immune response needs to be clarified. Also, an important question is why NTHi seems to be a commensal in the nasopharynx but turns into a potential strong inducer of inflammation in the lung. The answers to these questions may have important therapeutic implications.
The research team believes that more effort should be made towards the understanding of NTHi pathology and the body’s immune response. In the review, the team establishes priority areas that deserve future investigation, including the development of representative animal models of infection to more closely study the clinical phenotype and more detailed analysis of the human lung responses to NTHi infection.