Peripheral immune profiling identifies developmental immune displacement into an HLA-DR-low monocyte state in necrotizing enterocolitis.

Background: Necrotizing enterocolitis (NEC) is a devastating inflammatory disease of prematurity, yet how it reshapes systemic immunity relative to normal postnatal immune maturation remains unclear. We sought to define the peripheral immune architecture of NEC within a developmental framework and to evaluate whether its dominant signal could be linked to intestinal pathology. Methods: We performed high-dimensional Cytometry by Time-of-Flight profiling on 45 peripheral blood samples from 40 preterm infants spanning birth, postnatal control, pre-onset NEC, NEC onset, and post-onset NEC. Peripheral immune states were modeled relative to a birth-to-postnatal developmental reference trajectory. Key findings were further examined in publicly available intestinal single-cell and bulk transcriptomic datasets, and monocyte human leukocyte antigen-DR (HLA-DR) intensity was assessed as a simplified protein-level metric. Results: Twenty-seven immune cell subtypes were resolved across major lymphoid and myeloid compartments. In controls, peripheral immunity followed a stereotyped transition from early myeloid predominance toward lymphoid expansion after birth. NEC onset was associated with marked deviation from this trajectory and was dominated by expansion of HLA-DR-low CD16-negative monocytes, contraction of naive and regulatory T-cell subsets, and rewiring of immune correlations toward a myeloid-centered network. Cross-platform analyses supported concordance between the peripheral HLA-DR-low monocyte signal and inflammatory intestinal myeloid states with reduced antigen-presentation programs. Lower monocyte HLA-DR correlated with inflammatory severity; an exploratory within-cohort ROC analysis yielded an area under the curve of 0.84 (95% confidence interval 0.65-0.99). Conclusions: NEC is associated with developmentally discordant systemic immune remodeling centered on an HLA-DR-low monocyte state in blood, with concordant intestinal myeloid signatures in independent datasets. Monocyte HLA-DR may serve as a mechanistically anchored candidate readout for immune monitoring in preterm infants with NEC, pending external validation.