Bactericidal mechanisms of human breast milk leukocytes

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Abstract
The functional capacity of human breast milk phagocytes was evaluated with bactericidal and biochemical assays. Acridine orange was used as a vital stain for bacteria [Salmonella enteritidis or Staphylococcus aureus] to directly visualize phagocytosis and killing. Bactericidal capabilities were further examined by colony count and chemiluminescent methods. Cytocentrifuged specimens stained for myeloperoxidase exhibited enzyme activity in breast milk leukocytes equal to that of peripheral neutrophils. A radioisotopic assay of hexose monophosphate shunt activity demonstrated metabolic activity in breast milk leukocytes greater than that in peripheral blood neutrophils. The chemiluminescent response of breast cells was negligible, apparently the result of quenching secondary to fat present in the milk; pre-incubation of human blood leukocytes with the fatty layer of breast milk produced similar inhibition in the chemiluminescence assay. By most parameters, breast milk phagocytes are at least equal to blood neutrophils.