Interactions between innate and adaptive immune functions in neonatal macrophages (MΦ) are still unclear. We therefore established a method to quantify bacterial phagocytosis and intracellular degradation, using green fluorescent protein (GFP)‐labeled Escherichia coli in combination with phenotypic analysis. The kinetics of the proportion of phagocyting MΦ, phagocytosed bacteria per MΦ, and bacterial degradation were comparable for cord blood MΦ of term neonates and MΦ of healthy adults. Phenotyping revealed CD14 and CD16 to be down‐modulated within minutes. GFP‐labeled E. coli may be useful tools to further study MΦ subpopulations and determinants of phagocytosis in cord blood MΦ. © 2006 International Society for Analytical Cytology

Monocyte-derived macrophage (M⌽) subsets are generated by antagonistic induction pathways. A helper M⌽-type (Mh-M⌽) is induced by interferon gamma (IFN-␥), whereas a cytotoxic M⌽-type (Mc-M⌽), induced by interleukin-10 (IL-10), is a potent mediator of antibody-dependent cellular cytotoxicity (ADCC). Compared with M⌽ from healthy adults [peripheral blood monocyte-derived macrophages (PBM⌽)], cord blood M⌽ (CBM⌽) were found less capable of generating Mh-M⌽. Here we tested the hypothesis that their generation of Mc-M⌽ via IL-10 is also impaired. M⌽ surface markers were phenotyped. IL-10 protein and mRNA production were detected after stimulation [␣CD3 monoclonal antibody (mAb)]. CBM⌽ or PBM⌽ were co-cultured with M⌽-depleted mononuclear cells of adults and CD4-targeting antibodies as models for ADCC were added. In cord blood, we found diminished ␣CD3-induced IL-10 protein and mRNA production (p Ͻ 0.05 versus adults). Basal CD16 and HLA-DR expressions on CBM⌽ of preterm and full-term neonates were lower (p Ͻ 0.05 versus PBM⌽). IL-10 had reduced effects on CD16 up-and HLA-DR down-modulation on CBM⌽ (p Ͻ 0.05 versus PBM⌽). CD4-directed receptor modulation and deletion were reduced in the presence of CBM⌽ (p Ͻ 0.05 versus PBM⌽). IL-10 failed to enhance their ADCC capacity, which was in contrast to PBM⌽ (p Ͻ 0.05). These data suggest that CBM⌽ have an impaired cytotoxic capacity via lower sensitivity toward IL-10. (Pediatr Res 60: 152-157, 2006)

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