Non-typeable Haemophilus influenzae Protein D (None)

Protein D is a highly conserved 42 kDa surface lipoprotein present in all strains of *Haemophilus influenzae*, including both encapsulated and nonencapsulated (nontypeable, NTHi) forms. It is located on the outer membrane of the bacterium and plays a significant role in its pathogenicity, particularly in respiratory tract infections such as otitis media and exacerbations of chronic obstructive pulmonary disease (COPD). It acts as a virulence factor by impairing ciliary function, promoting bacterial adhesion and invasion, and possessing glycerophosphodiester phosphodiesterase activity. Due to its high conservation, surface exposure, and role in pathogenesis, protein D has been extensively studied as a vaccine candidate and is used as a carrier protein in conjugate vaccines like Synflorix™.

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