Protein D of Haemophilus influenzae (Protein D (PD))

Protein D of Haemophilus influenzae is a highly conserved, 42-kDa surface-exposed outer membrane lipoprotein found in both typeable and nontypeable (NTHi) strains of H. influenzae[7][1][3]. Protein D exhibits glycerophosphodiester phosphodiesterase enzymatic activity, leading to the release of glycerophosphorylcholine from host epithelial cells, and functions as a virulence factor by facilitating bacterial adhesion, invasion, and pathogenesis, particularly in the respiratory tract[7][1]. By impairing ciliary function in the airway, Protein D contributes to the bacterium's ability to cause diseases like acute otitis media, sinusitis, conjunctivitis, and exacerbations of COPD[3][7]. Due to its high conservation and surface exposure, Protein D is an attractive vaccine candidate and has served as a carrier protein in investigational pneumococcal conjugate vaccines, which have demonstrated partial protection against NTHi infections in both animal models and humans[7][3][1]. No small-molecule drugs are currently known to target Protein D; immunological intervention via vaccination remains the primary mode of therapeutically targeting this protein[7][3][1].

Other names

Protein DHaemophilus influenzae Protein DNTHi Protein DOuter membrane protein Dhpd gene product

Vaccine antigen/carrier: Induces protective antibody responses against NTHi; promotes opsonization and enhanced clearance of bacteria from host tissues[7][1]. The enzyme function (glycerophosphodiesterase) may be exploited in certain mechanistic studies; clinical targeting is via immune modulation.