NAD+ helps innate immune cells hold their memory

Clinical takeaway: NAD+ is a supplement that patients may be taking for purported muscle recovery and aging benefits. It appears to keep macrophages primed by inhibiting an enzyme that strips their chemical tags. 

Researchers have spent more than a decade studying how macrophages and other first-line immune cells, once thought to lack memory, can respond more vigorously to a second threat months after the first. Both infection and vaccination can trigger this phenomenon, known as trained immunity. Part of the mechanism involves a chemical tag on the histone proteins around which DNA is wrapped. These tags keep inflammatory genes poised for rapid activation.

Enzymes known as demethylases continually remove these tags from gene promoters, leaving it unclear how they persist over time. It was also unknown whether NAD+ (nicotinamide adenine dinucleotide), best known as a coenzyme in cellular metabolism, plays a role in trained immunity. In humans, a recent phase 3 trial of an NAD+-boosting supplement for early Parkinson disease missed the mark, with symptom scores worsening relative to placebo. This laboratory study, conducted in cultured macrophages and mice, examined whether NAD+ helps preserve these epigenetic tags by protecting them from removal.

Priming macrophages with β-glucan, a fungal compound known to induce trained immunity, increased nuclear NAD+ levels. Blocking or deleting the enzyme responsible for NAD+ production weakened the cells' enhanced response to a second exposure and reduced the epigenetic tag at inflammatory genes. NMN (nicotinamide mononucleotide), an NAD+ precursor, partially restored NAD+ levels in mouse macrophages and reversed the effects of enzyme inhibition in both mouse macrophages and human monocytes from healthy donors.

NAD+ acted directly on the enzyme. In test-tube experiments, NAD+ slowed the activity of KDM5A, an enzyme that removes the tag. Purified KDM5A bound NAD+ only in the presence of its histone target. Among the related enzymes tested, only KDM5A silencing partially restored the response in macrophages lacking the NAD+-producing enzyme. A mutant form of KDM5A that could not bind NAD+ continued stripping tags and suppressed the enhanced immune response more than the normal enzyme did.

β-glucan slowed melanoma growth in young mice but lost much of that effect in aged mice. Administered NMN restored the antitumor effect, whereas NMN alone did not inhibit tumor growth.

Researchers at Sun Yat-sen University Cancer Center conducted experiments in cultured mouse macrophages, test-tube assays, mice, and monocytes from healthy human donors. Each mouse comparison included five or six animals per group, either young or aged, along with untreated controls. Melanoma growth was tracked for about two and a half weeks. The mutant-enzyme experiments were performed in a mouse macrophage cell line rather than in primary cells.

An accompanying commentary highlights two key next questions. One is whether restoring NAD+ to normal levels can reestablish the histone tag in aged macrophages. The other is whether NAD+ acts in blood stem cells, where long-term trained immunity is thought to be established, or only in mature immune cells like those studied here. Both questions can be addressed with existing experimental tools. The commentary authors also caution that the goal in humans should be to restore, not exceed, normal NAD+ levels, as animal studies raise the possibility that chronically elevated levels could promote cancer.

“Nuclear NAD+ declines with age, which may be one reason that innate immune responsiveness degrades across the life span,” the commentary authors argue. “The goal therefore should be homeostasis rather than maximization, and evidence-based guidelines for achieving that goal in humans are not yet available.” 

Source: Jin H, et al. (2026 Oct 30) Sci Immunol. Nuclear NAD+ promotes innate immune memory by inhibiting KDM5A-dependent histone demethylation