The Colonization Strategies of Nontypeable Haemophilus influenzae - Bacterial Colonization Factors and Vaccine Development

Abstract: Nontypeable Haemophilus influenzae (NTHi) is a remarkably proficient colonizer of the human respiratory tract. The aim of this thesis has been to characterize currently known, and identify novel, bacterial factors involved in the key processes of colonization and pathogenesis, namely adherence to host tissue and evasion of the host innate immunity.

We have shown that the NTHi virulence factor Protein E mediates innate immune evasion by interacting with the C-terminus of host complement down-regulatory protein vitronectin. This interaction delayed the formation of the membrane attack complex on the bacterial surface and increased the bacterial serum-resistance. Furthermore, we identified a novel surface-exposed virulence factor designated Haemophilus Protein F that also sequesters vitronectin on the surface of the bacteria, thus rendering the pathogen more serum-resistant. Moreover, we have revealed that Protein F mediates bacterial adherence to primary human bronchial cells and to the extracellular matrix protein laminin. Isogenic mutants devoid of Protein F were observed to adhere significantly less to vitronectin, epithelial cells and laminin. These interactions were characterized at the molecular level, and the N-terminus of Protein F was shown to contain the host-interacting region. Finally, we showed that immunization with Protein F conferred increased pulmonary clearance of NTHi in vivo.

In summary, we have identified, and at the molecular level characterized, novel virulence factors that may be suitable for future vaccine development.