Impaired functional capacity of polarised neonatal macrophages

Neonatal sepsis is accompanied by impaired apoptotic depletion of monocytes and macrophages (M Phi), aberrant cytokine production, impaired cell metabolism, and sustained inflammation. Macrophage-colony stimulating factor (M-CSF) triggers the differentiation from monocytes into M Phi (M Phi-0). Interleukin-10 (IL10) and Interferon-gamma (IFNy) further differentiate M Phi subpopulations, the anti-inflammatory MM Phi-IL10 and the pro-inflammatory M Phi-IFNy subtype. We previously have shown significant differences between adult (PBM Phi) and cord blood (CBM Phi) in the metabolism of all subtypes. To test the hypothesis whether the competence to differentiate monocytes into M Phi-0 and to polarise into M Phi-IFNy and M Phi-IL10 was diminished in CBM Phi as compared to PBM Phi, we polarised monocytes by cultivation with M-CSF for 72 h, followed by stimulation with IFNy or IL10, for 48 h. After flow cytometry based immunotyping, we tested four functions: Phagocytosis of GFP-E. coli, uptake of erythrocytes, T-cell proliferation, induction of regulatory T-cells as well as phosphorylation analysis of AKT and STAT1/STAT3. Phosphorylation of STAT-1 and STAT-3, obligatory to differentiate into M Phi-IFN gamma, M Phi-0 and MM Phi-IL10, was found to be aberrant in CBM Phi. Whereas infected M Phi-0 showed identical phagocytic indices and intracellular degradation, TLR4-expression, NFkB up-regulation, IL10-, IL6-, and TNF alpha production of CBM Phi-0 were reduced. In addition, the capacity to bind aged erythrocytes and the consecutive IL10 production was lower in CBM Phi-IL10. Polarised PBM Phi-IFNy and PBM Phi-IL10 expressed higher levels of co-stimulatory receptors (CD80, CD86), had a higher capacity to stimulate T-cells and induced higher amounts of regulatory T-cells (all p < 0.05 vs. corresponding CBMF). Hypoxia-inducible-factor-1 alpha (HIF-1 alpha) was stronger expressed in CBM Phi-IFNy and upregulated in infected CBM Phi-0, whereas heme-oxygenase 1 (HO-1) expression was similar to adult PBM Phi. Neonatal M Phi-0, M Phi-IFNy and M Phi-IL10 polarisation is impaired with respect to phenotype and functions tested which may contribute to sustained inflammation in neonatal sepsis.