Gut microbiome imbalance expands inflammatory dendritic cells, triggering early autoimmunity

Long before lupus announces itself with swollen joints and damaged kidneys, long before type 1 diabetes destroys enough insulin-producing cells to push blood sugar upward, the immune system has already crossed an invisible line. Autoantibodies targeting the body’s own tissues appear in the blood years ahead of any symptom, marking a shadowy interval that clinicians call preclinical autoimmunity. What pushes a healthy immune system across that line has remained one of immunology’s most stubborn puzzles. A new study published in September 2026 in Nature Immunology now points to a surprising accomplice at the crossroads of two of medicine’s hottest research areas: the gut microbiome and a rare, inflammatory branch of the dendritic cell family. Led by first author Goran Cvijetic and colleagues, the research shows that when the gut’s microbial community collapses into dysbiosis, a distinctive population of AXL-positive type 3 dendritic cells expands dramatically, and this expansion is enough to set the earliest wheels of autoimmunity in motion—before a single clinical sign appears.

At the heart of the finding lies a causal chain. The team reports that microbial imbalance does not merely correlate with autoimmunity; it actively drives the buildup of a specialized antigen-presenting cell, and once this cell becomes numerically dominant, it is sufficient to convert a tolerant immune system into one that begins manufacturing antibodies against the body’s own molecules. In their experiments, shifts in the composition of the gut microbiota triggered the accumulation of AXL-positive inflammatory type 3 dendritic cells, and the rise of this population preceded the emergence of hallmark signatures of autoimmunity. Critically, when the expansion of these cells was prevented, the preclinical autoimmune cascade failed to ignite—a result that places the dendritic cell subset in the role of trigger rather than passive bystander. The discovery reframes dysbiosis as something far more concrete than a vague background risk factor: a precise upstream event that selects for and amplifies a dangerous cellular intermediary with the power to re-educate the adaptive immune system against its own host.

Dendritic cells are the immune system’s professional intelligence officers. Positioned in tissues throughout the body, they continuously sample their surroundings, engulfing proteins, microbes and cellular debris, then travel to lymph nodes to present fragments of what they have found on major histocompatibility complex molecules. There, with an arsenal of costimulatory signals, they decide whether a naïve T cell is ignored, deleted, or unleashed. For two decades, immunologists sorted these cells into three broad branches: classical type 1 dendritic cells, which excel at cross-presenting antigen to killer CD8 T cells; classical type 2 dendritic cells, which specialize in priming helper CD4 T cells; and plasmacytoid dendritic cells, the body’s factories for antiviral type I interferon. More recently, a fourth identity has crystallized: type 3 dendritic cells, or DC3s, a branch with monocyte-like origins that straddles the boundary between macrophage-lineage cells and classical dendritic cells. DC3s carry AXL and SIGLEC6 on their surface, depend on granulocyte-macrophage colony-stimulating factor for their development, and are exceptional producers of the inflammatory cytokines interleukin-12, interleukin-1 beta and tumor necrosis factor—making them among the most potent T-cell activators in the body.

The AXL molecule at the center of the new study belongs to the TAM family of receptor tyrosine kinases—TYRO3, AXL and MERTK—a trio best known for calming inflammation rather than igniting it. When TAM receptors bind their ligands, Gas6 and Protein S, which latch onto phosphatidylserine exposed on the surface of dying cells, they trigger the engulfment of apoptotic debris and simultaneously dampen signaling through toll-like receptors, the sensors that normally sound the alarm during infection. In most immune contexts, this machinery promotes tolerance and resolution. The paradox, then, is that AXL has emerged as the identity badge of the most inflammatory dendritic cell subset yet described. One possibility is that these cells exploit AXL signaling to survive and function amid the apoptotic debris and tissue damage that accumulate during chronic inflammation, effectively turning an anti-inflammatory receptor into a lifeline for a pro-inflammatory cell. Whatever its exact role, AXL gives researchers a molecular handle—a surface marker that can be used to track, isolate and potentially pharmacologically target this troublesome population.

To understand how these cells come to dominate, one has to look at what a healthy gut normally does. A balanced microbiome ferments dietary fiber into short-chain fatty acids such as butyrate, which nourish the intestinal epithelium, reinforce the mucus layer, support immunoglobulin A production and actively encourage regulatory T cells—the peacekeepers of the immune system. Dysbiosis, whether driven by Western-style diets, antibiotics, chronic stress or infection, dismantles this architecture. Beneficial butyrate producers thin out, inflammation-friendly bacterial groups such as Proteobacteria expand, the epithelial barrier grows leaky, and microbial products like lipopolysaccharide and flagellin begin crossing into the underlying lamina propria and the portal circulation. There they engage innate sensors—toll-like receptors and NOD-like receptors—prompting epithelial and myeloid cells to release interleukin-6, interleukin-1 beta, tumor necrosis factor and granulocyte-macrophage colony-stimulating factor. This is precisely the developmental climate in which monocyte-like precursors are pushed down the inflammatory dendritic cell pathway. In effect, a dysbiotic gut manufactures the conditions under which AXL-positive type 3 dendritic cells flourish.

What happens once these cells proliferate helps explain how silent microbial chaos becomes organized immune rebellion. Expanded AXL-positive dendritic cells are expert antigen presenters, and in a dysbiotic gut they carry a mixture of self-derived antigens and microbial fragments—presented side by side on the same cell. This proximity creates ideal conditions for molecular mimicry, in which T cells activated against microbial sequences cross-react with structurally similar host proteins. The cytokine cocktail these cells secrete then dictates the direction of the response: interleukin-12 pushes toward inflammatory Th1-type immunity, while interleukin-6 and interleukin-1 beta, combined with transforming growth factor-beta, steer naïve T cells into Th17 lineages that are strongly implicated in tissue-directed autoimmunity. Armed with costimulatory molecules such as CD80 and CD86, these dendritic cells can also provide the licensing signals that help autoreactive B cells enter germinal centers, undergo class switching and mature into autoantibody-secreting plasma cells. Immunologists have long known that the serological footprints of autoimmunity—antinuclear and anti-double-stranded DNA antibodies years before lupus, islet autoantibodies years before type 1 diabetes, anti-citrullinated protein antibodies years before rheumatoid arthritis—appear during this preclinical window. The new work now supplies a cellular mechanism that can generate those footprints.

The significance of the finding extends well beyond one cell type. It identifies, for the first time in this framework, a concrete cellular intermediary standing between an ecological disturbance in the gut and the immunological escape that defines autoimmune disease. It also helps explain a long-standing puzzle: why dysbiosis alone is not enough. Microbial imbalance is remarkably common, yet only a fraction of people with disturbed microbiomes ever develop autoimmunity, suggesting that a second, patient-specific event is required. The expansion of AXL-positive type 3 dendritic cells may be exactly that event—a threshold response that converts a common environmental condition into a rare pathological trajectory. Equally important, the cells offer a measurable waypoint. The frequency of AXL-positive dendritic cells circulating in blood could serve as an early-warning biomarker, flagging individuals in whom dysbiosis has begun to translate into autoimmunity long before antibodies reach diagnostic levels or organs come under attack. Such a marker would also give clinical trials of preventive interventions something they have historically lacked: a measurable intermediate endpoint that can signal success months or years before hard clinical outcomes could ever be assessed.

The therapeutic implications cut along two lines. On the microbiome side, the study strengthens the case for interventions that restore ecological balance—diets rich in fermentable fiber, precisely formulated probiotics, and, in more extreme cases, carefully screened microbiota transfer—though such approaches remain blunt instruments until the specific dysbiotic signatures that drive dendritic cell expansion are identified. On the immunological side, the AXL molecule and the DC3 lineage itself become druggable targets. AXL inhibitors are already in clinical development, mostly as anticancer agents designed to block tumor-associated immune suppression, and repurposing this pharmacology to restrain pathological dendritic cell expansion is an obvious next step. Cytokine blockade—interleukin-1 beta inhibitors are already approved for other inflammatory diseases—offers a second angle. But any such strategy demands surgical precision. Dendritic cells are indispensable for antimicrobial defense, antiviral responses and vaccine efficacy, and a blunt depletion of inflammatory dendritic cells could leave patients defenseless. The more realistic goal is a narrow therapeutic window: intervene only when the AXL-positive population begins to expand, monitor its frequency in blood as a treatment endpoint, and shield the rest of the dendritic cell network.

The immediate next step is validation in humans. The expansion seen in experimental systems must now be demonstrated longitudinally in people—ideally in first-degree relatives of patients with lupus, type 1 diabetes or rheumatoid arthritis, cohorts in which autoantibodies can be tracked years before disease onset. If AXL-positive dendritic cell frequencies rise in parallel with—or precede—seroconversion, the biomarker case becomes compelling, and trials could then ask whether microbiome-restoring interventions pull the rogue population back down and erase early autoimmune signatures. Questions of reversibility loom large: once tolerance is breached, can it be rebuilt, or can the process only be frozen? There are also deeper implications. The study suggests that autoimmune disease may not begin in the joints, the pancreas or the kidney, but in the ecology of the gut, years before the first recognizable symptom. The same sentinels that normally teach the immune system patience can, under the wrong microbial conditions, become its most dangerous teachers. If confirmed, the work will push clinicians to think of autoimmunity the way cardiologists now think of atherosclerosis—as a chronic, interceptable process with a long preclinical phase in which the right intervention, applied early enough, could change the entire course of a disease before it ever declares itself.