A low molecular weight factor is a significant mediator of non-opsonic neutrophil activation by Helicobacter pylori

Helicobacter pylori is believed to trigger neutrophil activation through several factors, including the H. pylori neutrophil-activating protein (HpNAP). The aim of this study was to characterise the factors within H. pylori cell-free extracts that stimulate neutrophil activation. Neutrophil activation was found to be dose-dependent and exhibited considerable variation between different clinical isolates. Activity was attributable to more than one protein factor. A low mol. wt fraction of <3 kDa was found to contribute a large proportion of the neutrophil-stimulating activity within H. pylori cell-free extract. Additional activity was provided by a high mol. wt fraction, possibly representing HpNAP. An inhibition ELISA and neutralisation experiments failed to identify or exclude formyl methionyl leucyl phenylalanine as the active factor within the low mol. wt fraction. The importance of the putative, low mol. wt neutrophil-activating factor may have been overlooked by those studies that have used concentrated H. pylori extracts.