A new study published in Nature Communications by the team of Sarah Dimeloe at the University of Birmingham (UK) has uncovered a groundbreaking role for NAD in immune regulation. Through systematic in vitro and in vivo experiments, the research reveals for the first time how NRK1 controls CD4+ T-cell immunity, clarifying the core mechanism by which cytoplasmic NAD/NADP metabolism shapes immune cell activation, survival, and defense against infection. This discovery fills a key gap in NAD science and opens new therapeutic targets for autoimmune and infectious diseases.

NAD (nicotinamide adenine dinucleotide) is widely known as a star anti‑aging molecule tied to cellular metabolism and aging control. In fact, NAD is a ubiquitous redox cofactor that cycles between its oxidized form (NAD+) and reduced form (NADH), transferring electrons and supplying energy to power all cellular activities. For immune cells, especially CD4+ T cells that coordinate immune responses, NAD is an absolute necessity. When pathogens invade, CD4+ T cells activate rapidly, driving a sharp rise in metabolic demand with enhanced glycolysis and mitochondrial metabolism that rely heavily on NAD for energy and biosynthesis. NAD+ also serves as a critical substrate for enzymes such as SIRTs and PARPs, supporting cell survival and DNA repair. Equally important, NADP — produced by phosphorylation of NAD — is central to the cellular antioxidant system: it maintains reduced glutathione, clears excess reactive oxygen species (ROS) to prevent cell damage, and stops ROS from overactivating immune cells and triggering unnecessary inflammation. In short, the activation, function, and survival of CD4+ T cells all depend on precise NAD regulation, making NAD synthesis and distribution key to immune cell performance.
The study centers on NRK1 (nicotinamide riboside kinase 1), an enzyme that converts the NAD precursor nicotinamide riboside (NR) into NMN to fuel NAD synthesis via the salvage pathway. Experiments on human primary CD4+ T cells and genetically modified mice reveal three defining features of NRK1‑driven NAD regulation.

First of all, NRK1 is the main driver of NAD synthesis in activated CD4+ T cells: it is minimally expressed in resting cells but sharply upregulated via the CD3/CD28 pathway upon activation, peaking at 48 hours. Exogenous NR strongly boosts NAD levels in activated CD4+ T cells, and NRK1 can compensate even when other NAD pathways are blocked.
Secondly, NRK1 localizes to the cytoplasm, and the NAD it produces accumulates mainly in the cytoplasm, separate from mitochondria. Cells also upregulate cytoplasmic NMNAT1 and NADK1, quickly converting NRK1‑derived NAD into NADP to form a dedicated cytoplasmic NAD‑NADP pool.

Third, cytoplasmic NAD generated by NRK1 does not boost CD4+ T‑cell activation — it acts as a precise “brake.” Cytoplasmic NADP efficiently clears ROS, a key signal that drives CD4+ T‑cell activation and pro‑inflammatory cytokine secretion. With functional NRK1, sufficient NADP neutralizes ROS, curbing excess CD4+ T‑cell activity and lowering IFN‑γ and TNF‑α release. Without NRK1, NADP drops, ROS builds up, and overactive NFAT signaling pushes CD4+ T cells into a hyperactive state that floods the body with pro‑inflammatory signals. NAD regulation shows a clear threshold effect: NRK1 maintains baseline activation when other pathways fail, yet reins in responses when all systems are intact to keep immunity balanced.
In vivo experiments confirm the real‑world impact of this pathway. Mice with CD4+ T‑cell‑specific NRK1 deletion were infected with Cryptococcus and influenza A virus. In infected tissues, these mice showed drastically fewer effector CD4+ T cells because unchecked ROS caused DNA damage and poor survival, even though initial activation remained intact. Survival in non‑infected lymphoid tissue was unaffected, highlighting NRK1’s unique role in sustaining immune cells at infection sites.
Unsurprisingly, the mice’s ability to fight infection collapsed: Cryptococcus‑infected animals had much higher fungal burden in the brain, while influenza‑infected mice suffered more severe illness, greater weight loss, and fewer effector immune cells in draining lymph nodes. These results prove that cytoplasmic NAD control preserves CD4+ T‑cell survival and keeps immune activity balanced — strong enough to clear pathogens, but restrained enough to avoid inflammatory “collateral damage” to healthy tissue.
Long known as a longevity molecule for its roles in metabolism and aging, NAD emerges from this research as a vital immune balancer. It governs two critical forms of balance: metabolic‑immune balance, supporting the energy and biosynthesis demands of immune activation while preventing metabolic excess from disrupting immune function; and infection‑defense balance, enabling robust pathogen clearance without overactive inflammation or tissue harm. The key lies not only in NAD levels but also in its subcellular distribution: cytoplasmic NAD calibrates immune intensity, while mitochondrial NAD fuels energy production, with distinct pools working in tandem to tune immune cell behavior.
These findings point to a new therapeutic frontier: targeting NAD metabolism in CD4+ T cells, especially the cytoplasmic NRK1–NAD–NADP axis, to fine‑tune immune responses. For autoimmune conditions such as rheumatoid arthritis and psoriasis — driven by overactive CD4+ T cells and excess inflammation — NR supplementation or NRK1 activation could raise cytoplasmic NAD/NADP, neutralize ROS, and calm hyperactive immunity.
For chronic infections or immune deficiency, mild NRK1 inhibition might sustain CD4+ T‑cell activity to strengthen defense. The research also offers hope for fungal infections like cryptococcal meningitis, where brain CD4+ T‑cell survival is critical; targeting the NRK1 pathway could boost local immune function and improve outcomes. While still in the preclinical stage, this work elevates our understanding of NAD: this small molecule governs metabolism and aging, and also acts as a precision master regulator of immune defense.
Our immune system is healthiest when balanced, not overactivated. NAD is the hidden precision regulator inside immune cells, using metabolic signals to safeguard immune balance and protect the body.

References
Stavrou V, Ali M, Gudgeon N, et al. Cytoplasmic NAD/H synthesis via NRK1 regulates inflammatory capacity and promotes survival of CD4+ T cells. Nature Communications. 2026.