Characterization of human breast milk macrophages cytostatic for human cell lines

Approximately 40% of the cells in human early lactation milk possessed the characteristics of macrophages, being adherent, phagocytic, alpha napthyl acetate esterase positive, and possessing C3b and Fc receptors. These cells were also cytostatic for MDA 157, a cell line derived from a pleural effusion of human breast cancer, and HEL 23, a strain of human fetal lung fibroblasts. Investigations into the cytostatic phenomenon indicated that the cytostasis could not be mediated by macrophage-conditioned medium and that very close contact between breast milk macrophages and target cells was required. Cytostasis was not fully effective until 18 hr after the initial interaction between macrophages and target cells.