Protein D expression promotes the adherence and internalization of non-typeable Haemophilus influenzae into human monocytic cells

Research output: Contribution to journalArticle


Protein D, having a glycerol-3-phosphodiester phosphodiesterase activity, is found at the surface of all Haemophilus influenzae strains and is a possible virulence factor. In the present study, the involvement of protein D in the entry of NTHi into human monocytic cells is reported. Primary monocytes and the monocytic cell lines U-937 and THP-1 were infected with NTHi strain 772 and the mutant 772 Delta hpd 1 (lacking the gene for protein D). NTHi 772 adhered to and entered monocytic cells up to four-fold more efficiently compared to 772 Delta hpd 1. When an Escherichia coli transformant expressing protein D was incubated with monocytic cells, the number of intracellular bacteria increased 1.6-fold compared to protein D-deficient controls. Any correlation between internalization and phosphorylcholine expression was not detected. In conclusion, our data suggest that surface-expressed protein D promotes the adherence of NTHi to human monocytes leading to a higher number of internalized bacteria.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Infectious Medicine


  • non-typeable Haemophilus influenzae, internalization, glycerophosphodiester phosphodiesterase, protein D, monocytes
Original languageEnglish
Pages (from-to)151-158
JournalMicrobial Pathogenesis
Issue number3
Publication statusPublished - 2001
Publication categoryResearch