Skin, our largest organ, acts as a protective barrier against pathogens that try to invade our bodies while constantly monitoring for potential threats. In the skin’s outermost layer, the epidermis, reside keratinocytes, cells that detect danger and actively orchestrate the body’s immune response. How these cells perform this task in a localized manner and then communicate the message with the entire immune system had been a mystery, but now a team of researchers from China has uncovered the signaling pathway.
In their study, published in Nature, they report that a specific substance called farnesyl pyrophosphate (FPP), naturally produced in skin cells, acts as a powerful danger signal that tells the body to ramp up its immune responses.
Upon encountering threats such as skin infection or ultraviolet exposure, FPP accumulates in keratinocytes in a localized manner, meaning its effects are mainly limited to the specific site of infection or exposure.
The FPP then binds with TRPV3, a chemical sensor present in skin cells, triggering a train of biochemical signaling that travels to nearby lymph nodes, instructing the immune system to produce antibodies to fight the threat.
Pathway from skin cells to immune cells
When the skin is infected, exposed to harmful radiation, or pricked with an injection, its cells release molecules known as damage-associated molecular patterns and pathogen-associated molecular patterns. When skin cells pick up on these chemical signals, they release inflammatory molecules called alarmins, which activate local immune cells.
Studies have shown that intermediates of the mevalonate (MVA) pathway—a key metabolic process—are known to accumulate in conditions like Alzheimer’s disease and other inflammatory diseases.
Building on this, the researchers wanted to examine whether FPP, one such intermediate of the MVA pathway, can similarly accumulate in skin lesions and function as an alarmin.
For this study, they used mouse models to trigger skin infection and other stimuli, then tracked how skin cells responded.
They found that FPP rapidly builds up in keratinocytes when stress factors initiate an unfolded protein response that activates SREBF transcription factors responsible for regulating lipid metabolism, and which in turn end up driving stronger germinal center responses in nearby lymph nodes, where antibodies are produced.
The accumulated FPP binds to TRPV3, leading to an influx of calcium ions into the cells. This calcium signal increases the production of IgG antibodies by prompting keratinocytes to release IL-6 and CCL20.
IL-6 supports the development of T follicular helper cells, which are needed to drive the production of high-quality antibodies in lymph nodes, while CCL20 attracts dendritic immune cells that carry information about threats to other parts of the immune system.
The researchers also found that the FPP–TRPV3 signaling pathway is overactive in the skin lesions of patients with systemic lupus erythematosus (SLE). This heightened activity creates false alarms, leading to the overproduction of harmful autoantibodies and worsening of disease symptoms.
The researchers are hopeful that the detailed view of the FPP–TRPV3–IL-6/CCL20–germinal center signaling axis provided by this study can help identify new lupus therapies.
To fully establish this pathway, further studies in human cells are needed, alongside clinical research to evaluate its potential for targeted treatments and vaccine adjuvant development.
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Publication details
Zhenglin Ji et al, A metabolic alarmin from keratinocytes potentiates systemic humoral immunity, Nature (2026). DOI: 10.1038/s41586-026-10167-6
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Nature
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