Following exposure of granulocytes (PMN) to chemotactic factors in vitro, the cells will degranulate and aggregate and upon infusion of chemotactic factors in vivo animals will be rendered neutropenic. In order to assess whether the specific granule product lactoferrin (LF) could mediate PMN stickiness in vitro and in vivo, PMN were exposed to human LF in vitro and animals were infused with LF in vivo. LF at concentrations as low as 6 ug/ml aggregated human PMN and 12 ug/ml LF promoted their attachment to human umbilical endothelial (44 ± 4% control compared to 55 ± 4% LF-treated). Infusion of 1 mg/kg LF into rabbits caused a 40% fall in PMN count by 2 min; whereas 2 mg/kg of transferrin or granule lysozyme lacked any effect. In order to visually assess the effect of LF, the hampster cheek pouch was prepared for in vivo microcirculation observation by displaying a venule on a TV-monitor. The number of PMN passing a segment of the venule was then determined. Within 20-30 seconds after administration of 70 to 280 ug rabbit LF/100g to hampsters the PMN rolling frequency markedly decreased. PMN stickiness was then sustained for 3-5 min. In contrast intravenous administration of albumin or transferrin lacked effect. These studies indicate that the PMN LF can sustain PMN autostickiness and serve to mediate the effect of chemotactic factor in rendering animals neutropenic.

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Boxer, L., Bjorksten, B., Bjork, J. et al. 794 LACTOFERRIN: MEDIATOR OF GRANULOCYTE STICKINESS IN VIVO. Pediatr Res 15, 574 (1981). https://doi.org/10.1203/00006450-198104001-00818

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