An anti-inflammatory protein called IL-38 was lower in macrophages grown from aged mice, and restoring it in the laboratory reduced several aging-associated signs of cellular stress. The findings point to a possible regulator of chronic inflammation in aging. They do not show that IL-38 is an anti-aging treatment.
What researchers discovered
Macrophages are immune cells that engulf microbes and debris and help coordinate inflammation and tissue repair. They communicate partly through cytokines, small signaling proteins that can increase or restrain immune activity.
IL-38 is a cytokine with anti-inflammatory effects in several experimental settings. In the new peer-reviewed study in Immunity & Ageing, researchers found less IL-38 in macrophages derived from old mice than in cells from young mice.
The aged cells also showed more inflammatory signaling, reactive oxygen species and DNA-damage-associated changes. Proteins involved in halting the cell cycle, including p16 and p21, were higher, while several proteins that normally help cells move through the cell cycle were lower.
These changes overlap with inflammaging, the persistent low-grade inflammatory state that often develops with age and is associated with many chronic diseases. They are markers of altered cell behavior, not proof that the cells alone caused disease or whole-body aging.
How they tested it
The experiments did not treat living aged animals. Researchers collected bone marrow from 8-week-old and 80-week-old female mice, then grew the cells for seven days to produce bone-marrow-derived macrophages. All IL-38 interventions occurred in culture.
When aged macrophages received recombinant IL-38 for 48 hours, inflammatory cytokines and activation of NF-kB declined. NF-kB is a signaling system that helps cells switch on inflammatory genes in response to stress or infection. Persistent NF-kB activity is one contributor to chronic age-related inflammation.
IL-38 treatment also reduced reactive oxygen species, DNA-damage-associated gamma-H2AX signals and senescence-associated beta-galactosidase staining. Cell-cycle regulators shifted partway toward the pattern seen in young cells. The authors describe partial normalization, not a complete reversal of cellular aging.
The team also used RNA interference to lower IL-38 in young macrophages. Those cells developed more inflammatory and senescence-associated features, including higher NF-kB activity and p21, plus lower levels of proteins that support cell-cycle progression.
Finally, an NF-kB inhibitor produced changes similar to IL-38 in aged cells. Combining the two did not add much benefit, which is consistent with overlapping activity. It does not yet prove that NF-kB is the only route through which IL-38 acts.
Why it could matter
Macrophages change with age and can contribute to impaired tissue repair, altered immune defense and chronic inflammation. A signal that helps keep their inflammatory response in balance could be biologically important.
The study is strongest as a mechanistic clue. Increasing IL-38 and reducing it pushed several cell measurements in opposite directions. That pattern supports a functional role for the cytokine rather than a simple correlation.
It also fits a broader research effort to understand how immune aging and cellular senescence interact. Our recent coverage of cGAS, chromatin and healthspan in mice examines another inflammatory pathway whose effects depend heavily on biological context.
What the study does not prove
This was a small ex vivo study, meaning cells were removed from animals and studied outside the body. Most comparisons used three to five independent biological samples, and only female mice were included.
Growing bone marrow cells for seven days may itself influence differentiation, proliferation and stress signals. The results also may not represent macrophages that live permanently in tissues such as the brain, liver or lung.
No aged mouse received IL-38, so the study cannot show whether the cytokine reaches relevant tissues, improves immune function, changes disease risk or produces unacceptable side effects in a living organism. There is no evidence here from human cells or patients.
The findings therefore do not support taking IL-38 as a supplement or treatment. Therapeutic relevance would require suitable delivery, dosing, safety and durable benefit, none of which this experiment tested.
What comes next
Researchers will need to confirm the findings in fresh and tissue-resident macrophages, test both sexes and determine more precisely how IL-38 interacts with NF-kB and other pathways. Studies in living aged animals would then need to measure immune function and meaningful tissue outcomes, not only molecular markers.
Human relevance is a later question. That would begin with human macrophages from well-characterized donors and careful studies of whether IL-38 activity tracks inflammatory function. Any therapeutic program would still need pharmacology, toxicology and controlled clinical testing.
The current result is a useful cellular signal: IL-38 helped aged mouse macrophages look less inflammatory under laboratory conditions. It is not evidence of rejuvenation in an animal or a person.