PHAGOCYTIC FUNCTIONS Oh HUMAN MILK MACROPHAGES

Abstract

Human milk is a suspension of viable cells; macrophages ( Mφ) are the most abundant cells, comprising 40-80 % of the total cell count. The present study was initiated to examine the principal cell functions of phagocytic milk Mφ: adherence, chemotaxis, killing and phagocytosis-associated oxidative metabolism. Adherence of milk Mφ to nylon wool was significantly decreased when compared with blood monocytes, chemotaxis of Mφ in response to C5a or a synthetic chemotactic peptide was also decreased. However, Mφ generated luminol-dependent luminescence, superoxide anion O₂⁻ and hydrogen peroxide (H₂O₂) to a similar extend as blood monocytes after stimulation with opsonized zymosan or phorbol myristate acetate (PMA). In addition, Mφ killed Escherichia coli and Staphylococcus aureus as effectively as did blood monocytes (∼75 %, 120 min). Acidification of milk (pH 1, 30 min) only slightly reduced PMA-stimulated production of oxygen radicals by Mφ. Bacterial killing by Mφ preincubated at pH 1 was about 70 % that from controls maintained at pH 7. When Mφ were cultured for several days in endotoxin-free medium, their ability to produce oxygen metabolites declined. By continuous treatment with bacterial lipopolysaccharide (LPS, 10 ng/ml), milk Mφ could be “primed” to release large amounts of oxygen intermediates. The O₂⁻ response of Mφ cultured without bacterial products could be partially restored by the addition of LPS to the culture. We conclude that milk Mφ are capable of releasing large amounts of oxygen metabolites, and could contribute to the protection of neonates against bacterial and fungal infections.

Supported by a grant from Deutsche Forschungsgemeinschaft

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