Does immune activation increase demand for one‑carbon metabolism?

Immune activation triggers a rapid metabolic shift characterized by the intensive expansion of the one-carbon (1C) metabolism network. This metabolic reprogramming is essential for transforming quiescent lymphocytes into highly proliferative effector cells, providing the necessary substrates for genomic replication and epigenetic regulation.

Clinical and physiological evidence

During an immune response, particularly the activation of T cells, there is a coordinated upregulation of enzymes within the folate and methionine cycles, including DHFR, TYMS, and MTHFD2. This upregulation supports the massive clonal expansion required to fight infection or respond to injury.

• Proliferative demand: Activated CD8+ T cells exhibit a dramatic increase in anabolic flux to facilitate rapid cell division.
• Nucleotide biosynthesis: Research indicates that one-carbon metabolism is the primary source of 10-formyl-tetrahydrofolate for purine synthesis and 5,10-methylene-tetrahydrofolate for thymidylate (dTMP) production.
• Growth limitations: Studies demonstrate that inhibiting 1C flux (e.g., via methotrexate) or depleting essential precursors leads to uracil misincorporation into DNA, DNA damage, and cell cycle arrest at the G1 phase.

Mechanistic explanations

One-carbon metabolism functions as a critical junction for transferring carbon units to support two major cellular requirements:

• DNA Synthesis: The folate cycle provides the carbon skeletons necessary for de novo nucleotide synthesis. Doubling the cellular genome during the S-phase of the cell cycle requires an acute supply of deoxyribonucleotide triphosphates (dNTPs).
• Methylation and Epigenetics: The methionine cycle generates S-adenosylmethionine (SAM), the cell's universal methyl donor. Immune activation triggers extensive epigenetic remodeling, where SAM is used to methylate histones (such as H3K4) and DNA. These modifications are indispensable for T-cell differentiation and the expression of effector genes.
• Metabolic Sensing: The SAM/SAH (S-adenosylhomocysteine) ratio serves as a metabolic sensor; a high ratio promotes the methylation required for Th1 cell differentiation, while a low ratio or SAM depletion impairs immune gene expression and functional capacity.

Bottom line

Immune activation significantly increases the demand for one-carbon metabolism. This pathway is a non-negotiable requirement for providing the nucleotide precursors for DNA synthesis and the methyl donors for epigenetic programming, both of which are essential for immune cell proliferation and functional response.