Haemophilus influenzae Type f Hijacks Vitronectin Using Protein H To Resist Host Innate Immunity and Adhere to Pulmonary Epithelial Cells

Abstract

The incidence of invasive Haemophilus influenzae type b (Hib) disease has significantly decreased since the introduction of an efficient vaccine against Hib. However, in contrast to Hib, infections caused by H. influenzae serotype f (Hif) are emerging. We recently did a whole genome sequencing of an invasive Hif isolate, and reported that Hif interacts with factor H by expressing protein H (PH). In this study, upon screening with various human complement regulators, we revealed that PH is also a receptor for vitronectin (Vn), an abundant plasma protein that regulates the terminal pathway of the human complement system in addition to being a component of the extracellular matrix. Bacterial Vn binding was significantly reduced when the lph gene encoding PH was deleted in an invasive Hif isolate. The dissociation constant (KD) of the interaction between recombinant PH and Vn was 2.2 μM, as revealed by Biolayer interferometry. We found that PH has different regions for simultaneous interaction with both Vn and factor H, and that it recognized the C-terminal part of Vn (aa 352–362). Importantly, PH-dependent Vn binding resulted in better survival of the wild-type Hif or PH-expressing Escherichia coli when exposed to human serum. Finally, we observed that PH mediated an increased bacterial adherence to alveolar epithelial cells in the presence of Vn. In conclusion, our study reveals that PH most likely plays an important role in Hif pathogenesis by increasing serum resistance and adhesion to the airways.

Hijacking Complement Regulatory Proteins for Bacterial Immune Evasion

“…Binding of Hsf to HBD3 of Vn was mediated via aa 429-652 of Hsf (Singh et al, 2014; Figure 6A). Protein H is another protein expressed by Hib, as well as by the newly emerging Hif, involved in mediating serum resistance through binding of Vn (Al-Jubair et al, 2015). NTHi strains have evolved to express distinct Vn-binding proteins namely Protein E and Protein F (Hallström et al, 2009; Singh et al, 2013; Su et al, 2013).…”

“…Furthermore, PspC of S. pneumoniae can bind Vn and FH. Additional proteins that bind multiple regulatory proteins include H. influenzae Protein H, S. aureus SdrE, S. pneumoniae Hic and Yersinia Ail (Sharp et al, 2012; Hair et al, 2013; Fleury et al, 2014; Ho et al, 2014; Kohler et al, 2014; Al-Jubair et al, 2015). Proteins that bind multiple complement regulators to the bacterial surface will be of high importance to bacterial survival.…”

Host–pathogen interactions of nontypeable Haemophilus influenzae: from commensal to pathogen

“…However, recent evidence suggests increased incidence of infections related to H. influenzae type a, e, and f, although at a lesser number than NTHi . Notably, proteins such as protein H and Haemophilus surface fibrils (Hsf) are examples of virulence factors not detected in NTHi, that we have found to be important for encapsulated H. influenzae virulence.…”

Moonlighting of Helicobacter pylori catalase protects against complement-mediated killing by utilising the host molecule vitronectin

“…Normal human serum (NHS) was obtained from healthy volunteers of unknown H. pylori infection status. Depletion of Vn was accomplished by running serum against anti-Vn-coupled CNBr Sepharose as described previously 45 . Western blotting was used to confirm depletion of Vn and to ensure that levels of serum-antibodies were unaffected by the depletion process.…”