Haemophilus influenzae P4 interacts with extracellular matrix proteins promoting adhesion and serum resistance.

Interaction with the extracellular matrix (ECM) is one of the successful colonization strategies employed by non-typeable Haemophilus influenzae (NTHi). Here we identified Haemophilus lipoprotein 4 (P4) as a receptor for ECM proteins. Purified recombinant P4 displayed a high binding affinity for laminin (Kd=9.26 nM) and fibronectin (Kd=10.19 nM), but slightly less to vitronectin (Kd=16.51 nM). A P4-deficient NTHi mutant showed a significantly decreased binding to these ECM components. Vitronectin acquisition conferred serum resistance to both P4-expressing NTHi and Escherichia coli transformants. P4-mediated bacterial adherence to pharynx, type II alveolar and bronchial epithelial cells was mainly attributed to fibronectin. Importantly, a significantly reduced bacterial infection was observed in the middle ear of the Junbo mouse model when NTHi was devoid of P4. In conclusion, our data provide new insight into the role of P4 as an important factor for Haemophilus colonization and subsequent respiratory tract infection.