The importance of a beta-glucan receptor in the nonopsonic entry of nontypeable Haemophilus influenzae into human monocytic and epithelial cells

Previous reports showed that nontypeable Haemophilus influenzae (NTHi) resi de in macrophage-like cells in human adenoid tissue. This study investigate d the ability of nonopsonized NTHi and encapsulated H. influenzae type b (H ib) to enter human monocytic and epithelial cells. The number of intracellu lar bacteria was determined by a viability assay and flow cytometry. To cha racterize the mechanisms responsible for the internalization of NTHi, diffe rent inhibitors of surface molecules, receptor turnover, and the cytoskelet on were used. Hib were found in monocytic cells at very low numbers (<100 b acteria/2 x 10(5) cells). In contrast, a great variation in intracellular n umbers was detected between the different NTHi isolates (range, 0.0007%- 0. 28% of the inoculum for monocytes and 0.053%-3.5% for epithelial cells). NT Hi entered human monocytic and epithelial cells via a receptor-mediated end ocytosis involving mainly a <beta>-glucan receptor that could be blocked by laminarin.