The Haemophilus influenzae Hap serine protease promotes adherence and microcolony formation, potentiated by a soluble host protein

Haemophilus influenzae initiates infection by colonizing the upper respirat ory mucosa. The process of colonization involves adherence to epithelium an d evasion of host immunity. in this study, we examined the H. influenzae Ma p adhesin, which has serine protease activity and undergoes autoproteolytic cleavage and extracellular release in broth, We found that the uncleaved c ell-associated form of Hap mediates adherence to cultured epithelial cells and promotes bacterial aggregation and microcolony formation. Adherence and aggregation are augmented by secretory leukocyte protease inhibitor, a nat ural component of respiratory secretions that inhibits nag autoproteolysis. These observations suggest a never paradigm in host-pathogen relations, in which a soluble host protein whose primary function is to protect host epi thelium potentiates properties that facilitate bacterial colonization.