MOTILITY OF HUMAN MILK LEUKOCYTES IN COLLAGEN GELS

Abstract

We previously reported that adherence, orientation and directed movement of human milk leukocytes (HMLs) were less than peripheral blood leukocytes (PBLs). Since the diminished motility may have been due to a decrease in adherence, a collagen gel (CG) system where leukocyte movement is less dependent on adherence was used to explore these questions.

Unfractionated HMLs or fractionated PBLs were placed on CGs in microwells and the leading edge of migration was determined by inverted phase microscopy. The mean rates of invasion of HMLs, blood neutrophils and mononuclear blood leukocytes were 20, 200, and <1 )μ/H, respectively (p<0.01). We then examined the identity of motile HMLs by immunoperoxidase techniques by using antibodies to selected cell markers. Motile HMLs were positive for neutrophil and monocyte markers Mac-1, lysozyme, and a specific macrophage marker cathepsin B, but were negative for markers for lymphocytes (Leu1), NK cells (Leu7) and neutrophils (cathepsin G). The motility of these cells was inhibited (<1μ/H; p<0.001) when unfractionated HMLs were stimulated with a T cell lectin (PHA) to produce lymphokines, e.g. migration inhibitory factor.

Thus, the diminished motility of milk neutrophils does not appear to be due to decreased adherence per se. Furthermore, those HMLs which are motile are macrophages. The findings suggest a dichotomy for the function of HMLs. Neutrophils may be relegated to the lumen of the alimentary tract, whereas macrophages may penetrate into mucosal sites for host defense.

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