Scientists Found the Body's Natural Off Switch for Inflammation

Inflammation gets a great deal of attention as a cause of chronic disease, but a quieter and equally important question is rarely asked: why does it not turn off? The immune system does not stay switched on forever after every cut or infection. In most cases, acute inflammation does its job, clears the threat, and then resolves. The resolution phase is not passive. It is an active, tightly orchestrated biological process that requires specific molecular signals to execute. When those signals are absent or insufficient, inflammation can become self-sustaining. That is the state we call chronic low-grade inflammation, and a growing body of evidence ties it to heart disease, metabolic dysfunction, autoimmune conditions, and neurodegenerative disease.

A September 2026 study published in Nature Communications by researchers at UCL and collaborating institutions, including King's College London, the University of Oxford, Queen Mary University of London, and the National Institute of Environmental Health Sciences at the NIH in the United States, has now identified a specific molecular switch that plays a central role in telling the immune system to stop. That switch involves a group of fat-derived molecules called epoxy-oxylipins, and it operates through a pathway that most people have never heard of. Understanding it offers a new lens for thinking about why chronic inflammation persists and what that means for general wellness monitoring.

What the UCL Study Found

To study how inflammation resolves in living humans, the UCL team used a carefully controlled experimental model. Participants received a tiny injection of ultraviolet-killed Escherichia coli bacteria into the forearm. Because the bacteria were dead, they could trigger an immune response but could not cause an infection. This produced a localized, predictable bout of acute inflammation that researchers could track in detail from start to finish, measuring both the molecular changes happening at the injection site and the behavior of immune cells in the bloodstream.

The team mapped what happened to a class of lipid molecules called epoxy-oxylipins throughout the inflammatory cycle. These molecules are derived from fatty acids in cell membranes and are produced by a family of enzymes known as cytochrome P450s. They found that epoxy-oxylipins were present in the blood of healthy volunteers at baseline and that their concentrations changed in specific ways as inflammation progressed and resolved. The enzymes that break down these molecules, collectively called epoxide hydrolases, were also highly active at the site of inflammation, with different isoforms rising and falling at different times during the response.

To test whether boosting epoxy-oxylipin levels would accelerate resolution, the researchers used a drug called GSK2256294. This compound selectively inhibits soluble epoxide hydrolase, or sEH, which is the enzyme that normally degrades epoxy-oxylipins. By blocking their breakdown, the drug allows these molecules to accumulate. When given to participants at specific stages of the inflammatory response, GSK2256294 significantly raised levels of two key epoxy-oxylipins, 12,13-EpOME and 14,15-EET. The result was faster pain resolution and a significant reduction in intermediate monocytes, a class of immune cell that expands during inflammation. The drug did not change visible signs like tissue heat, redness, or swelling, suggesting it was specifically accelerating the immune resolution process rather than simply suppressing all inflammation indiscriminately (Bracken et al., Nature Communications, 2026).

What Are Epoxy-Oxylipins?

Epoxy-oxylipins belong to a broader family of bioactive fat-derived molecules called oxylipins. The body produces dozens of these compounds from polyunsaturated fatty acids, including arachidonic acid and linoleic acid, using several different enzyme families. Some oxylipins are well-known pro-inflammatory mediators. Prostaglandins, for instance, are oxylipins produced via the COX enzymes that drive the pain, swelling, and heat of acute inflammation, and are the same molecules that aspirin and ibuprofen block. The epoxy-oxylipins studied by the UCL team are produced through a different branch of this metabolic tree, the cytochrome P450 pathway, and they appear to have largely opposite, pro-resolving effects.

The broader category of molecules that help resolve inflammation is now often called specialized pro-resolving mediators, or SPMs. Resolvins, protectins, and lipoxins are among the best-characterized SPMs, and the scientific community's understanding of this class has grown substantially in the past two decades, much of it built on foundational work by Charles Serhan and colleagues at Harvard. A major review in Nature Reviews Cardiology summarized the evidence that SPMs, including epoxy-oxylipins, initiate anti-inflammatory and pro-resolving actions, and that without an effective and timely resolution response, inflammation can become chronic, a pathological state associated with many widely occurring human diseases, including atherosclerotic cardiovascular disease (Fredman and Serhan, Nature Reviews Cardiology, 2024). The UCL study adds a new molecular player to this family and, critically, demonstrates the mechanism in living human volunteers rather than just in cells or animals.

The specific mechanism the UCL team uncovered involves a protein signaling pathway called p38 MAPK. One of the key epoxy-oxylipins, 12,13-EpOME, was found to block the conversion of classical monocytes into intermediate monocytes by suppressing p38 MAPK activity. This pathway is a central regulator of inflammatory gene expression in immune cells. When p38 MAPK is active, monocytes can transform into an intermediate, pro-inflammatory form. When 12,13-EpOME suppresses p38 MAPK, that transformation is slowed. This finding was replicated in laboratory cell cultures and confirmed in human volunteers given a separate p38 MAPK inhibitor drug, providing independent evidence that the mechanism is real and not a coincidental correlation.

The Role of Intermediate Monocytes

Monocytes are white blood cells that circulate in the blood and serve as key regulators of the immune response. They come in three main subtypes: classical monocytes, which are the most abundant and first responders; intermediate monocytes, which are elevated during inflammation; and nonclassical monocytes, which tend to have a patrolling, surveillance role. Under normal circumstances, classical monocytes transform into intermediate monocytes during an acute immune response, amplifying the inflammatory signal. Once the threat is cleared, these cells are supposed to revert or die off, allowing the immune system to stand down.

When this process goes wrong, intermediate monocytes accumulate and contribute to sustained inflammation. Elevated intermediate monocyte counts have been observed in several chronic inflammatory and autoimmune conditions, and they have been linked to higher levels of inflammatory cytokines. The UCL study showed that boosting epoxy-oxylipin levels with GSK2256294 significantly reduced the expansion of these cells during the controlled inflammatory challenge, suggesting that the epoxy-oxylipin pathway helps regulate how many of these cells accumulate. Fewer intermediate monocytes were also found at the site of inflammation itself, alongside reduced tissue levels of CD4 T cells, another type of immune cell involved in sustaining inflammatory activity.

This immune-regulatory effect is distinct from simple anti-inflammatory suppression. Many existing drugs, including corticosteroids and non-steroidal anti-inflammatory drugs, work by broadly dampening inflammatory activity. The epoxy-oxylipin pathway appears to be more precisely targeted: it tells specific immune cells to complete their transition back to a resting state rather than simply blocking the entire immune cascade. This matters because indiscriminate immune suppression can impair the body's ability to fight infection and heal tissue. A resolution-promoting approach, in theory, would guide the immune response to a natural conclusion without leaving the person more vulnerable to pathogens.

Why Chronic Inflammation Persists When This Switch Fails

The UCL study reinforces a model of chronic inflammation that has been gaining traction in the research community: it is not just too much inflammation being switched on, but too little being switched off. For years, the dominant therapeutic approach to inflammatory disease focused on blocking pro-inflammatory mediators. Drugs that inhibit TNF-alpha, IL-6, or the NLRP3 inflammasome have genuinely transformed outcomes in conditions like rheumatoid arthritis. But a complementary explanation is that many people with persistent low-grade inflammation have a failure of the natural resolution process, not just an overactive pro-inflammatory pathway. Both problems can produce the same elevated CRP reading on a blood test, but they call for different solutions.

Evidence from cardiovascular research illustrates the downstream consequences of unresolved inflammation. A large systematic review and meta-analysis of 81 studies found that elevated CRP and interleukin-6 were consistently associated with significantly higher risks of all-cause mortality and cardiovascular events in people with chronic kidney disease, with CRP linked to a 63% higher risk of all-cause mortality and a 57% higher risk of cardiovascular events (Abdel-Rahman et al., European Journal of Internal Medicine, 2025). These associations reflect, at least in part, the cumulative damage of inflammation that the body's resolution machinery failed to clear. The persistent CRP elevation seen in these patients is not just a marker of active disease, it is a signal that the off switch may not be working properly.

Diet and lifestyle factors that support anti-inflammatory health may, in part, work by supporting this resolution process. Omega-3 fatty acids, for example, are precursors to several specialized pro-resolving mediators, including resolvins. This is one mechanistic reason why diets rich in oily fish, consistent physical activity, and maintenance of a healthy body weight are associated with lower systemic inflammation in population studies. They may not just reduce the intensity of acute inflammatory responses but also improve the efficiency with which those responses resolve. The UCL study adds to this picture by identifying another molecular route through which the body accomplishes resolution, and suggesting that the epoxy-oxylipin pathway may be amenable to targeted support.

What This Means for Future Treatments

The most immediate implication of the UCL study is a potential new therapeutic target for chronic inflammatory conditions. The drug GSK2256294 used in the study is a selective sEH inhibitor, and several compounds in this class have been in development for cardiovascular and metabolic conditions for a number of years. By demonstrating that sEH inhibition accelerates inflammatory resolution specifically through the intermediate monocyte pathway in humans, the study provides mechanistic support for exploring these drugs in conditions where unresolved inflammation is a central driver of harm.

Conditions that could eventually benefit from this approach include rheumatoid arthritis, cardiovascular disease, metabolic syndrome, and chronic pain disorders. In each of these, persistent immune activation and elevated inflammatory markers are hallmarks of the disease state. A drug that promotes natural resolution rather than suppressing the entire immune system could offer therapeutic benefits with a more targeted side effect profile than broad immunosuppressants. That said, the current study was conducted in healthy volunteers with induced acute inflammation, and a long path of clinical development lies between these findings and approved treatments for any specific disease.

The discovery also adds scientific weight to the value of measuring resolution-relevant inflammation markers over time. CRP, the most widely used marker of systemic inflammation, captures the net state of inflammatory activity rather than its cause. Whether inflammation is high because the pro-inflammatory switch is jammed on or because the resolution switch is broken, CRP will be elevated in either case. Tracking CRP over weeks and months, and correlating changes with lifestyle adjustments, gives a practical window into whether the inflammatory system as a whole is trending in a healthier direction. Because CRP is a general wellness marker rather than a diagnostic tool, persistent elevations are always worth discussing with a healthcare provider.

Why Monitoring Inflammation Trends Matters

For most people, the practical application of this science is a renewed appreciation for why inflammation levels vary from week to week and why tracking them over time is more meaningful than a single measurement. The body is continuously cycling through acute inflammatory responses, whether from a minor illness, a hard workout, a stressful period, or a poor night of sleep, and the efficiency of the resolution phase shapes how quickly CRP returns to baseline afterward. A person whose resolution machinery is working well will tend to have lower average CRP levels because each inflammatory episode concludes more quickly. A person whose resolution is impaired may see persistently elevated readings even without an obvious acute trigger.

Several factors that affect the body's capacity for inflammation resolution are accessible to lifestyle change. Getting adequate polyunsaturated fats, particularly omega-3 fatty acids from fish and other sources, provides the raw material for pro-resolving lipid mediators including the epoxy-oxylipin precursors highlighted in the UCL study. Regular moderate physical activity has been shown to promote anti-inflammatory and pro-resolving signaling. Managing chronic stress through sleep, social connection, and relaxation practices reduces the persistent activation of immune pathways that competes with natural resolution. None of these changes are medical treatments, and none should be mistaken for substitutes for medical care, but they represent the lifestyle foundation on which a healthier inflammatory system is built.

The UCL epoxy-oxylipin finding is a reminder that inflammation science is still revealing how complex and active the body's regulatory systems are. The immune system does not just attack; it also knows when to stop. Understanding how that stop mechanism works, and how to support it, is one of the more promising frontiers in chronic disease prevention. Following your inflammation levels with a general wellness tool like an at-home CRP test can help you understand how these dynamics play out in your own body over time, and give you concrete, shareable data to bring to conversations with your healthcare team.

Sources

• Bracken OV, Jalali P, Glanville JRW, et al. Epoxy-oxylipins direct monocyte fate in inflammatory resolution in humans. Nature Communications, 2026; 17(1):431. pubmed.ncbi.nlm.nih.gov/41545341
• Fredman G, Serhan CN. Specialized pro-resolving mediators in vascular inflammation and atherosclerotic cardiovascular disease. Nature Reviews Cardiology, 2024; 21(11):808-823. pubmed.ncbi.nlm.nih.gov/38216693
• Abdel-Rahman SM, Ozbek L, Narin AE, et al. Association between interleukin-6, C-reactive protein and chronic kidney disease outcomes: A systematic review and meta-analysis. European Journal of Internal Medicine, 2025; 145:106669. pubmed.ncbi.nlm.nih.gov/41449012
• ScienceDaily. Scientists discover a hidden switch that shuts down inflammation. September 12, 2026. sciencedaily.com

Frequently Asked Questions

What is inflammation resolution and why does it matter?

Inflammation resolution is the active biological process by which the immune system stands down after an acute inflammatory response. It is not simply the absence of inflammation but a coordinated set of molecular events involving specialized signaling molecules that suppress pro-inflammatory immune activity, remove cellular debris, and restore tissue to a normal state. When resolution works properly, CRP returns to baseline and the immune system is ready for the next challenge. When it fails, inflammation persists at a low level indefinitely, and this chronic state is associated with cardiovascular disease, metabolic disorders, and other chronic conditions.

What are epoxy-oxylipins?

Epoxy-oxylipins are fat-derived signaling molecules produced in the body from polyunsaturated fatty acids, primarily through a family of enzymes called cytochrome P450s. They are part of a larger class of compounds called specialized pro-resolving mediators that help bring acute inflammation to an end. A September 2026 study in Nature Communications showed that one specific epoxy-oxylipin, 12,13-EpOME, suppresses the expansion of pro-inflammatory intermediate monocytes by blocking a protein signaling pathway called p38 MAPK, a mechanism confirmed in both human volunteers and laboratory cell cultures.

What are intermediate monocytes and why do they matter for chronic inflammation?

Intermediate monocytes are a subtype of white blood cell that expand during acute inflammation as part of the immune response. Under normal circumstances, they decline once the inflammatory stimulus is cleared. When inflammation fails to resolve, intermediate monocytes can remain elevated, contributing to sustained inflammatory signaling. The UCL study found that boosting epoxy-oxylipin levels in human volunteers significantly reduced the expansion of intermediate monocytes and also lowered their numbers at the site of inflammation, suggesting that these molecules play a direct role in guiding the resolution process.

Can a CRP test tell me if my inflammation has resolved?

C-reactive protein, or CRP, rises and falls with systemic inflammatory activity, so tracking it over time gives a practical picture of whether inflammation is resolving or persisting. After an acute trigger such as an illness or a hard workout, CRP typically peaks and then returns to its personal baseline over days to a few weeks in people with healthy resolution. If CRP remains elevated for extended periods without an obvious cause, it may reflect chronic low-grade inflammation worth discussing with a healthcare provider. Sensa is a general wellness tool designed to make regular CRP monitoring accessible at home, providing longitudinal data rather than a single snapshot.