Persistence of nontypeable Haemophilus influenzae in adenoid macrophages: a putative colonization mechanism

Area of Science:

• Microbiology
• Immunology
• Otolaryngology

Background:

• Nontypeable Haemophilus influenzae (NTHI) is a common cause of upper respiratory tract infections in children.
• The intracellular presence of NTHI in adenoid tissue has been hypothesized but not definitively demonstrated.
• Understanding NTHI's tissue-level interactions is crucial for elucidating its persistence mechanisms.

Purpose of the Study:

• To investigate the intracellular location of NTHI within human adenoid tissue.
• To characterize the host cells harboring NTHI in the adenoid microenvironment.
• To explore the role of intracellular NTHI in nasopharyngeal colonization.

Main Methods:

• Utilized fluorescence in situ hybridization (FISH) with a 16S rRNA-targeted probe to detect H. influenzae.
• Employed immunohistochemistry with a monoclonal antibody (MAHI-3) specific to H. influenzae.
• Performed simultaneous FISH and immunophenotypic staining (e.g., CD14) to identify host cell types.

Main Results:

• H. influenzae was detected intracellularly in macrophage-like cells in all 43 adenoid tissue samples examined.
• NTHI was found in subepithelial locations within the adenoid crypts.
• A significant proportion of these cells expressed the CD14 marker, indicative of monocyte/macrophage lineage.

Conclusions:

• NTHI resides intracellularly within human adenoid tissues, primarily in cells of the monocyte/macrophage lineage.
• This intracellular presence likely plays a significant role in NTHI's ability to colonize and persist in the nasopharynx.
• The findings provide a cellular basis for understanding NTHI persistence in children's upper respiratory tracts.