Plasmacytoid Dendritic Cells Exhibit High Transferrin Receptor Expression Without Iron Accumulation.

Plasmacytoid dendritic cells (pDCs) are specialized antiviral sentinels defined by rapid type I interferon (IFN‑I) production, yet their proteomic organization and metabolic requirements remain incompletely understood. We established the steady‑state proteome of murine splenic pDCs directly ex vivo using deep, absolute quantitative mass spectrometry and compared it with conventional dendritic cell subsets and human pDCs. pDCs exhibited a highly conserved proteomic architecture across species, with selective divergence in central carbon metabolism, amino‑acid utilization, and nutrient transporter expression. Notably, pDCs expressed exceptionally high levels of the transferrin receptor (TFRC) in both mice and humans and displayed robust transferrin‑mediated iron uptake relative to other splenic immune populations. Despite this, pDCs did not demonstrate increased total cellular iron or enhanced ferritin‑based storage. Instead, proteome‑wide iron mapping revealed preferential allocation of iron to functional iron-sulfur and heme‑containing proteins, particularly within mitochondrial pathways. Detection of the iron exporter ferroportin indicated coordinated iron import and efflux, establishing sustained iron flux rather than net accumulation. Functional assays showed that iron availability does not constrain TLR9‑induced IFN‑I or TNF production. Together, these data define a conserved iron‑handling program in pDCs characterized by high TFRC expression, balanced iron flux, and targeted redistribution into essential protein systems.