Inhibition ofHumanNeutrophil Migration InVitro byLow- Molecular-Mass Products ofNontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae commonlycausesinfections inthelowerandupper respiratory tract, although themechanisms ofitscolonization andpersistence intheairways areunclear. Culture filtrates from sixclinical isolates ofthis bacterium were assessed fortheir abilities toinfluence neutrophil function invitro. Eachculture filtrate was assessed on sixseparate occasions withneutrophils obtained fromsixdifferent donors. During thelogandearlystationary phases ofgrowth (0to18h),culture filtrates contained primarily neutrophil chemokinetic activity butno activity affecting neutrophil migration toward thechemotactic factors N-formyl- L-methionyl-L-leucyl-L-phenylalanine andleukotriene B4.Incontrast, filtrates obtained after 24 hofculture contained factors whichinhibited neutrophil migration towardbothofthesechemotactic factors. This chemotaxis-inhibitory activity persisted between 24and72hofbacterial culture, anditwas notassociated with thepresenceofeither chemotactic orchemokinetic activity asassessed bycheckerboard analysis. Gelfiltration ofpooled 72-hfiltrates yielded three majorpeaksofchemotaxis-inhibitory activity. Endotoxin was present together withtwootherlow-molecular-mass hydrophobic factors ofapproximately 8 and2 kDa.These low-molecular-mass factors arechloroform insoluble andheatstable, andthey areinactivated byprotease, periodate, anddiborane reduction. Activity was completely retained on awheatgerm agglutinin column, and itcould beeluted withN-acetyl-D-glucosamine. Thesedatasuggest thatinhibitory activity isassociated with N-acetyl-D-glucosamine-containing glycopeptides, possibly derived fromthebacterial cell wall. Theproduction ofthesecompounds may contribute tothepersistence ofthisbacterium invivobyinhibiting neutrophil chemotaxis inthemicroenvironment oftherespiratory mucosa.