Flammulina velutipes NF-κB: Two Pathways, One Mushroom

Enoki Inflammation and Immunomodulation

2 independent mechanisms

A 2025 study identified RSAD2, a protein typically associated with antiviral defense, as the key mediator through which F. velutipes polysaccharides activate NF-κB and MAPK signaling.

Wang et al., International Journal of Biological Macromolecules, 2025

FIP-fve Protein

activates T-cells via MAP2K3/p38α kinase chain (Gu 2022)

RSAD2/Viperin

newly identified NF-κB/MAPK mediator in enoki polysaccharide research (Wang 2025)

TLR4 → NF-κB

suppressed by F. velutipes in DSS-induced IBD mouse model (Nguepi 2023)

Wang et al., International Journal of Biological Macromolecules, 2025

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The immune system uses molecular keys to open signaling doors. Most functional food compounds carry one key and fit one lock. Flammulina velutipes, the mushroom behind enoki, carries two structurally unrelated compounds that enter the body's inflammatory signaling through completely different gates. Research mapping the Flammulina velutipes NF-κB pathway has accumulated across 30 years of laboratory work, with the most precise mechanistic findings arriving as recently as 2022, 2023, and 2025.

This article covers the pathway biology in depth: what the two mechanisms are, how they differ at the molecular level, and what animal models tell us about whether those mechanisms produce real anti-inflammatory effects. For a broader picture of enoki's health evidence, see What Is Enoki Mushroom? The Tiny Mushroom with Big Research.

The Dual-Mechanism Story: Why This Mushroom Runs Two Parallel Immune Programs

Most foods that influence immune signaling do so through one compound acting on one molecular target. Flammulina velutipes contains two bioactive classes that operate entirely independently.

The first is FIP-fve (Fungal Immunomodulatory Protein from Flammulina velutipes). It is a protein, 114 amino acids long, with a galectin-like folding structure. Galectins are a family of carbohydrate-binding proteins that animals use to regulate immune cell activity and inflammatory responses. Ko et al. isolated and fully characterized FIP-fve in 1995, establishing its amino acid sequence and identifying the galectin-like structural domain. FIP-fve acts on T-cells. It does not suppress inflammation directly; it modulates the way T-cells produce signaling molecules, which shapes the broader inflammatory environment.

The second is a family of beta-glucan polysaccharides, extracted from both the fruiting body and mycelium of F. velutipes. Yin et al. demonstrated in 2010 that purified mycelial polysaccharides stimulate macrophage proliferation and cytokine output directly in cell culture.^[2] These compounds act on a completely different cell type, through a completely different receptor family, compared to FIP-fve's T-cell activation route. Macrophages are the immune system's front-line responders. T-cells are adaptive immune cells that coordinate longer-term immune programs. Activating one does not activate the other through the same molecular path.

The significance is that these are not variants of the same mechanism. They are two independent programs. Research over the past decade has mapped both with enough precision to name the individual kinase nodes involved, and the most recent studies have added details that were genuinely unexpected even to researchers in the field.

For context on how enoki's inflammation evidence compares across different conditions and how the two mechanisms contribute differently, see Enoki and Inflammation: Anti-Inflammatory Mechanisms.

The Polysaccharide Route: TLR4, NF-κB, and a 2025 Discovery That Surprised Researchers

The general shape of the polysaccharide pathway was understood before 2025: F. velutipes polysaccharides bind to pattern recognition receptors on macrophage surfaces, activate downstream signaling cascades, and produce cytokines that coordinate immune responses. The receptor involved is TLR4 (Toll-like receptor 4), a surface protein that normally detects molecular patterns from bacterial cell walls. When TLR4 activates, it signals through a protein called MyD88 to NF-κB, the master regulator of inflammatory gene expression.

Nguepi et al. confirmed in 2023 that F. velutipes reduces DSS-induced IBD severity and protects the liver from IBD-associated injury by suppressing TLR4/NF-κB signaling in mice.^[7] The polysaccharide fraction was reducing the inflammatory signal at the TLR4 entry point, before it could propagate through MyD88 and produce TNF-α and IL-6.

The 2025 mechanistic study by Wang et al. went significantly deeper. Researchers isolated a specific F. velutipes polysaccharide called FVP-1 and tested it in RAW264.7 macrophage cells and mouse spleen cells.^[9] FVP-1 activated NF-κB and MAPK signaling. That was the expected result. But the mechanism used to get there was not what anyone had mapped before. The key mediator was RSAD2.

A 2024 study by Jia et al. added further structural context. Researchers characterized a novel F. velutipes polysaccharide with a distinct molecular architecture and confirmed both immunomodulatory and lipid-lowering activity in cell models.^[8] This added to an accumulating picture: enoki produces not a single polysaccharide but a family of structurally distinct polysaccharides, and the ones studied so far consistently show immunological activity through the same basic TLR4/NF-κB/MAPK architecture.

The two-pathway picture, summarized:

The RSAD2 Discovery: When an Antiviral Gene Shows Up in an Anti-Inflammatory Study

RSAD2 is the gene name for viperin. It encodes an enzyme that cells produce when viruses invade. Viperin disrupts viral replication by interfering with lipid droplet formation and blocking viral particles from exiting cells. Interferon signaling turns it on. Before 2025, nearly all RSAD2 research was in the context of viral infection and antiviral immunity.

Wang et al. found RSAD2 upregulated in macrophages treated with FVP-1, and then knocked it down to see what happened.^[9] Silencing the RSAD2 gene significantly reduced FVP-1's ability to activate NF-κB and MAPK. The conclusion was not ambiguous: RSAD2 was not a bystander gene that happened to be expressed. It was a required intermediate. Without it, the polysaccharide's downstream signaling collapsed.

This is a genuinely surprising finding for two reasons. First, no one had connected a mushroom polysaccharide to RSAD2 as a mechanistic node before. Second, the connection between carbohydrate-based immune compounds and a typically antiviral effector protein had not been established in macrophage activation research. The implication is that F. velutipes polysaccharide is triggering a cellular state in macrophages that resembles an antiviral response, and that this state is the route to NF-κB activation.

The antiviral body's signaling system, called type I interferons, is a potent activator of NF-κB. If polysaccharide treatment turns on a cellular program that includes RSAD2, which is normally part of the interferon-stimulated gene response, the downstream NF-κB activation would follow naturally from that connection.

What this adds to the field: the standard story for mushroom polysaccharide-driven macrophage activation has been TLR4 → MyD88 → NF-κB, treated as a relatively direct connection. Wang 2025 adds an unexpected RSAD2-mediated intermediate that links the TLR4 signal to the MAPK/NF-κB output. This detail puts enoki's polysaccharide research ahead of most other edible mushrooms in terms of mechanistic resolution, and it may explain why FVP-1 activates NF-κB at the specific magnitude it does.

For context on how enoki's polysaccharide compounds compare to the broader category of mushroom polysaccharides in immune cell activation, see Enoki Polysaccharides and Immune Cell Activation. For how enoki's polysaccharide mechanism differs from triterpene-based pathways in other mushrooms like reishi, see Triterpenes vs. Polysaccharides: Different Anti-Inflammatory Pathways.

The FIP-fve Route: How a Galectin-Like Protein Threads a Different Needle

While polysaccharides activate macrophages through pattern recognition receptors, FIP-fve enters the immune system through a different cell type and a different receptor. It targets T-cells, and it does so through a kinase cascade that has been progressively narrowed to specific molecular nodes over three decades of research.

Wang et al. established in 2004 that FIP-fve induces IFN-γ (interferon-gamma) production in T-cells by activating p38 MAPK phosphorylation.^[1] At the time, p38 MAPK was known as a central stress-response and cytokine-production node. The finding established that FIP-fve uses this node, but did not specify where in the p38 cascade the activation occurred. The p38 MAPK family has multiple upstream activators, and which one a compound uses determines a great deal about which cells respond and how.

Gu et al. answered that question in 2022. Testing FIP-fve in Jurkat cells, a human T-cell line used for immune signaling research, they found FIP-fve specifically activated MAP2K3.^[6] MAP2K3 is an upstream kinase that directly phosphorylates p38α, also called MAPK14. The output was IL-2 production and T-cell proliferation. The path now had named nodes: FIP-fve triggers MAP2K3, MAP2K3 activates p38α (MAPK14), and p38α drives IL-2 and IFN-γ production.

The specificity of MAP2K3 matters. The p38 MAPK family can be activated by several upstream kinases, including MAP2K6 and ASK1 as well. The fact that FIP-fve specifically engages MAP2K3 rather than MAP2K6 or ASK1 points to a defined interaction with particular signaling scaffolds in T-cells, and may explain why FIP-fve's immune effects appear more T-cell-selective than general macrophage-activating compounds.

FIP-fve also has a NF-κB dimension, but it operates from a different angle than the polysaccharide story. Chang et al. showed in 2013 that FIP-fve suppresses NF-κB activity in lung cancer cells by downregulating MMP-9.^[3] MMP-9 (matrix metalloproteinase-9) is a gene whose expression NF-κB drives upward during chronic inflammation. It promotes cell migration and tissue invasion. By reducing MMP-9, FIP-fve was reducing one of the downstream consequences of constitutively active NF-κB in a cancer cell context.

This creates an apparent paradox: polysaccharides activate NF-κB in macrophages, while FIP-fve reduces a key NF-κB output in cancer cells. The resolution is context. In a resting macrophage, NF-κB activation is part of a coordinated immune response; it produces cytokines that protect against pathogens. In a cancer cell with chronically overactive NF-κB, reducing gene expression downstream (like MMP-9) reduces invasive behavior. The same signaling pathway produces functionally opposite outcomes depending on which cell type it runs in and what its baseline activity level is.

For the complete FIP-fve story, including its galectin domain classification and the oral activity data that confirms it survives digestion in mice, see Enoki Galectin and NF-κB Pathway Modulation.

What These Pathways Look Like in an Inflamed Gut

Cell culture data establishes mechanisms. Animal models confirm that those mechanisms produce real physiological changes. The colitis studies provide that second layer of validation.

Zhang et al. showed in 2020 that F. velutipes polysaccharide reduced the severity of DSS-induced colitis in mice by restoring gut microbial balance and suppressing the pro-inflammatory cytokines TNF-α and IL-6.^[4] The distinctive finding was microbial: the polysaccharide increased Lactobacillus and Bifidobacterium populations in the gut, shifting the microbial environment in a direction that secondarily reduced inflammation driven by bacterial imbalance. The polysaccharide was acting partly as a prebiotic, not only as a direct anti-inflammatory agent.

A second 2020 study by Zhao et al. used a structurally different F. velutipes polysaccharide, a beta-type glycosidic compound rather than the compound in Zhang's study.^[5] It also reduced DSS-induced colitis and modulated gut microbiota, but appeared to act more directly on gut lining inflammation, rather than primarily through the microbiota correction route. The mechanisms overlapped but were not identical.

Two structurally different polysaccharides from the same mushroom, tested in the same animal colitis model, both producing anti-inflammatory outcomes through partially distinct routes. Convergent evidence from structurally non-identical compounds is harder to dismiss as a compound-specific artifact.

Nguepi et al.'s 2023 study extended the picture further. F. velutipes reduced not only colonic inflammation but also the liver injury that develops secondarily in IBD, and the mechanism was specifically TLR4/NF-κB suppression.^[7] This study most clearly connected the pathway-level mechanism, specifically TLR4 suppression reducing NF-κB activity, to a measurable disease model outcome. It also broadened the relevance of enoki's colitis research: the effects in these models are not limited to the gut lining but extend to systemic inflammatory stress.

For a dedicated deep-dive on the colitis evidence, including the comparison between Zhang 2020 and Zhao 2020's mechanisms, see Enoki and Gut Inflammation: Colitis Research. For how enoki's IBD evidence compares to other mushrooms' beta-glucan research, see How Mushrooms Fight Inflammation: NF-κB, COX-2, and Beyond.

The Evidence Boundary: What the Pathway Research Can't Answer

Mapping mechanisms in cells and mouse models is scientifically meaningful. It is also insufficient to answer the practical questions a person with an inflammatory condition would actually ask.

No human trials have tested F. velutipes extract against NF-κB, MAPK, or any downstream inflammatory marker. The dose-response relationship in humans is unknown. Whether the polysaccharide concentrations achievable through food consumption or standard supplement doses reach the levels needed to activate these pathways in vivo has not been established from clinical data. The RAW264.7 macrophage system is a well-validated model for macrophage biology, but it is a single transformed cell line, not a human immune system responding to diet.

The DSS-induced colitis model reliably produces intestinal inflammation, but it does not fully replicate the immunological complexity of human IBD. The two polysaccharides tested by Zhang 2020 and Zhao 2020 were isolated research compounds, not whole mushroom preparations or commercial supplements, which means the doses and formulations used are not directly comparable to anything commercially available.

What the research does clearly establish: F. velutipes contains compounds that activate or modulate specific, named signaling nodes (MAP2K3, p38α, RSAD2, TLR4, NF-κB) in laboratory conditions. The pathway architecture has been mapped with enough resolution to distinguish which kinase each compound uses and which cell types respond. That is a higher level of mechanistic specificity than most functional foods have achieved. It is also, as of 2026, still preclinical. The gap between pathway mapping and clinical evidence remains open.

For a condition-by-condition review of where enoki's preclinical evidence is strongest, see Enoki for Inflammatory Conditions: Research Review.

The Bottom Line

Flammulina velutipes modulates inflammatory signaling through two independent molecular pathways: FIP-fve protein activates T-cells via the MAP2K3/p38α MAPK chain (Gu 2022), while polysaccharides activate macrophage NF-κB/MAPK signaling through an RSAD2-mediated route identified in 2025 (Wang et al.). Animal colitis models confirm that these pathway activities produce measurable anti-inflammatory outcomes. All evidence is preclinical; no human trials exist for any enoki anti-inflammatory endpoint.

Frequently Asked Questions

What signaling pathways does Flammulina velutipes affect?

Flammulina velutipes affects two main signaling pathways through two structurally unrelated compounds. Polysaccharides activate the NF-κB/MAPK pathway in macrophages via TLR4 and an RSAD2-mediated intermediate. FIP-fve protein activates the p38 MAPK pathway in T-cells specifically through the MAP2K3/p38α kinase chain. These pathways operate in different immune cell types through different molecular intermediaries.

How does Flammulina velutipes polysaccharide activate macrophages?

F. velutipes polysaccharide binds TLR4 receptors on macrophage surfaces, triggering downstream NF-κB and MAPK signaling. A 2025 study by Wang et al. found that RSAD2, a gene normally associated with antiviral responses, is a necessary mediator in this process. Silencing RSAD2 significantly reduced the polysaccharide's ability to activate NF-κB and MAPK, establishing it as a required intermediate rather than a bystander effect.

What is RSAD2 and how does it relate to inflammation?

RSAD2 (also called viperin) encodes an antiviral enzyme that cells normally produce in response to viral infection. Wang et al. (2025) found that F. velutipes polysaccharide FVP-1 upregulates RSAD2 in macrophages, and that this upregulation mediates subsequent NF-κB and MAPK activation. The finding was unexpected because RSAD2's role had not previously been described in the context of mushroom polysaccharide-driven macrophage activation.

Does Flammulina velutipes suppress or activate NF-κB?

Both, depending on the compound and cell type. F. velutipes polysaccharides activate NF-κB in macrophages, consistent with coordinated immune activation. FIP-fve protein suppresses an NF-κB-driven output gene (MMP-9) in cancer cells, consistent with reducing chronic NF-κB-mediated inflammatory activity. The same signaling pathway produces opposite functional outcomes in different cellular contexts.

What is the difference between FIP-fve and Flammulina velutipes polysaccharides?

FIP-fve is a 114-amino-acid protein with a galectin-like folding structure that acts on T-cells through the MAP2K3/p38α kinase chain to produce IL-2 and IFN-γ. F. velutipes polysaccharides are carbohydrate chains that act on macrophages through TLR4 and RSAD2 to activate NF-κB and MAPK. They are structurally unrelated molecules, act on different immune cell types, use different cell-surface receptors, and engage different intracellular signaling intermediaries.

Sources & References

1. 1RTHM-00146·Wang, Po-Hui et al. (2004). “Fungal immunomodulatory protein from Flammulina velutipes induces interferon-gamma production through p38 mitogen-activated protein kinase signaling pathway..” Journal of agricultural and food chemistry.Study breakdown →PubMed →↩
2. 2RTHM-00372·Yin, Hongping et al. (2010). “Purification, characterization and immuno-modulating properties of polysaccharides isolated from Flammulina velutipes mycelium..” The American journal of Chinese medicine.Study breakdown →PubMed →↩
3. 3RTHM-00513·Chang, Yu-Chi et al. (2013). “Interruption of lung cancer cell migration and proliferation by fungal immunomodulatory protein FIP-fve from Flammulina velutipes..” Journal of agricultural and food chemistry.Study breakdown →PubMed →↩
4. 4RTHM-01312·Zhang, Rongjun et al. (2020). “Polysaccharide from flammuliana velutipes improves colitis via regulation of colonic microbial dysbiosis and inflammatory responses..” International journal of biological macromolecules.Study breakdown →PubMed →↩
5. 5RTHM-01316·Zhao, Ruiqiu et al. (2020). “Effects of a β-type glycosidic polysaccharide from Flammulina velutipes on anti-inflammation and gut microbiota modulation in colitis mice..” Food & function.Study breakdown →PubMed →↩
6. 6RTHM-01528·Gu, Kefei et al. (2022). “FIP-fve Stimulates Cell Proliferation and Enhances IL-2 Release by Activating MAP2K3/p38α (MAPK14) Signaling Pathway in Jurkat E6-1 Cells..” Frontiers in nutrition.Study breakdown →PubMed →↩
7. 7RTHM-01761·Nguepi Tsopmejio, Ivan Stève et al. (2023). “Auricularia polytricha and Flammulina velutipes reduce liver injury in DSS-induced Inflammatory Bowel Disease by improving inflammation, oxidative stress, and apoptosis through the regulation of TLR4/NF-κB signaling pathways..” The Journal of nutritional biochemistry.Study breakdown →PubMed →↩
8. 8RTHM-01910·Jia, Wei et al. (2024). “Structural Elucidation of a Polysaccharide from Flammulina velutipes and Its Lipid-Lowering and Immunomodulation Activities..” Polymers.Study breakdown →PubMed →↩
9. 9RTHM-02206·Wang, Qiuyi et al. (2025). “Flammulina velutipes polysaccharide exerts immunomodulatory function involving RSAD2 to regulate the NF-κB/MAPK signaling pathway in RAW264.7 macrophage cells and in mouse spleen cells..” International journal of biological macromolecules.Study breakdown →PubMed →↩