Proinflammatory effects of bacterial lipoprotein on human neutrophil activation status, function and cytotoxic potential in vitro

Bacterial lipoprotein (BLP) is the most abundant protein in gram-negative b acterial cell walls, heavily outweighing lipopolysaccharide (LPS). Herein w e present findings demonstrating the potent in vitro effects of BLP on neut rophil (PMN) activation status, function, and capacity to transmigrate an e ndothelial monolayer. PMNs are the principal effecters of the initial host response to injury or infection and constitute a significant threat to inva ding bacterial pathogens. The systemic inflammatory response syndrome (SIRS ) is characterised by significant host tissue injury mediated, in part, by uncontrolled regulation of PMN cytotoxic activity. We found that BLP-activa ted human PMN as evidenced by increased CD11b/CD18 (Mac-1) expression. Up-r egulation of PMN Mac-1 in response to BLP occurred independently of membran e-bound CD14 (mCD14). A similar up-regulation of intercellular adhesion mol ecule-1 (ICAM-1) on endothelial cells was observed whilst E-Selectin expres sion was unaffected. PMN transmigration across a human umbilical vein endot helial cell (HUVEC) monolayer was markedly increased after treating either PMN's or HUVEC independently with BLP. This increased transmigration did no t occur as a result of any direct effect of BLP on HUVEC monolayer permeabi lity, assessed objectively using the passage of FITC-labeled Dextran-70. BL P primed PMN for enhanced respiratory burst and superoxide anion production in response to PMA, but did not influence phagocytosis of opsonized Escher ichia coil. BLP far exceeds LPS as a gram-negative bacterial wall component , these findings therefore implicate BLP as an additional putative mediator of SIRS arising from gram-negative infection.