Interactions of Haemophilus influenzae with cultured human endothelial cells.

The interactions of capsulate (b+) and capsule-deficient (b-) Haemophilus influenzae type b with endothelial cells were studied in vitro using human umbilical vein endothelial cells (Huvecs). Association was determined by estimation of colony forming units (cfu) as well as the binding of 3H-thymidine-labelled bacteria. Bacteria associated with Huvecs rapidly and in a dose-dependent manner. The presence of capsule on bacteria resulted in a decrease in the rate of cell-association. Internationalisation of bacteria by Huvecs was quantitated after elimination of extracellular bacteria with gentamicin. It was found that larger numbers of b- bacteria were internalised compared to b+ bacteria. Incubation in the presence of metabolic inhibitors had little effect on the association of bacteria to Huvecs whereas internalisation was dependent on the integrity of host cellular functions. Electron microscopic studies confirmed phagocytic ingestion of both b+ and b- variants and suggested that the majority of the internalised bacteria remained viable within endothelial cell vacuoles. Haemophilus influenzae were translocated within vacuoles both from the apical to basal and the basal to apical direction.