Impaired functional capacity of polarised neonatal macrophages

Area of Science:

• Immunology
• Neonatal Medicine
• Cell Biology

Background:

• Neonatal sepsis is associated with defective monocyte and macrophage (MΦ) function, including impaired apoptosis, aberrant cytokine production, and altered cell metabolism, leading to sustained inflammation.
• Macrophage-colony stimulating factor (M-CSF) induces monocyte differentiation into MΦ (MΦ-0), while Interleukin-10 (IL10) and Interferon-gamma (IFNγ) polarize them into anti-inflammatory (MΦ-IL10) and pro-inflammatory (MΦ-IFNγ) subtypes, respectively.
• Previous studies indicated significant metabolic differences between adult (PBMΦ) and cord blood (CBMΦ) macrophages.

Purpose of the Study:

• To investigate whether the capacity of cord blood monocytes (CBMΦ) to differentiate into MΦ-0 and polarize into MΦ-IFNγ and MΦ-IL10 subtypes is diminished compared to adult peripheral blood monocytes (PBMΦ).
• To assess key macrophage functions, including phagocytosis, erythrocyte uptake, T-cell proliferation, and regulatory T-cell induction, in neonatal versus adult MΦ subtypes.

Main Methods:

• Monocytes from cord blood and adult peripheral blood were cultured with M-CSF for differentiation into MΦ-0, followed by stimulation with IFNγ or IL10 for polarization into MΦ-IFNγ and MΦ-IL10 subtypes.
• Flow cytometry was used for immunophenotyping.
• Functional assays included phagocytosis of GFP-E. coli, erythrocyte uptake, T-cell proliferation assays, regulatory T-cell induction, and analysis of AKT and STAT1/STAT3 phosphorylation.

Main Results:

• Aberrant phosphorylation of STAT-1 and STAT-3 was observed in CBMΦ, crucial for MΦ differentiation and polarization.
• While phagocytic capacity was similar, CBMΦ-0 exhibited reduced TLR4 expression, NFkB up-regulation, and production of IL10, IL6, and TNFα compared to PBMΦ-0.
• CBMΦ-IL10 showed reduced capacity for aged erythrocyte binding and IL10 production. Polarized PBMΦ subtypes displayed higher co-stimulatory receptor expression (CD80, CD86) and superior capacity to stimulate T-cells and induce regulatory T-cells compared to CBMΦ counterparts. Hypoxia-inducible-factor-1α (HIF-1α) was upregulated in CBMΦ-IFNγ and infected CBMΦ-0.

Conclusions:

• Neonatal monocyte-derived macrophages (MΦ-0, MΦ-IFNγ, MΦ-IL10) exhibit impaired polarization, altered signaling pathways (STAT1/STAT3), and reduced functional capacity compared to adult macrophages.
• These deficits in neonatal MΦ polarization phenotype and function may contribute to the sustained inflammation characteristic of neonatal sepsis.
• The findings highlight critical differences in neonatal versus adult innate immune cell responses, with implications for understanding and treating neonatal infections.