A team of researchers from Japan has uncovered a previously unknown immune mechanism that helps explain how allergies that begin in the skin can progress into severe, body-wide allergic reactions. The discovery sheds light on the biological events underlying the "atopic march" and could pave the way for new therapies aimed at preventing life-threatening allergic conditions.
The findings, published in the Proceedings of the National Academy of Sciences (PNAS), reveal that the immune signaling molecule interleukin-13 (IL-13) promotes systemic allergic responses by acting on type 2 classical dendritic cells (cDC2) rather than directly influencing B cells or T cells, as previously believed.
Uncovering the Mechanism Behind the Atopic March
The atopic march describes the progression of allergic diseases that often begins with atopic dermatitis (eczema) and later develops into conditions such as food allergies, asthma, and systemic allergic reactions. This progression starts when allergens enter the body through damaged skin, sensitizing the immune system.
Although several biologic therapies are already available to treat allergic diseases, the molecular events driving this transition have remained poorly understood.
Researchers from Tokyo University of Science and Kyoto University investigated this process using a mouse model that closely mimics cutaneous allergen sensitization. By repeatedly exposing the skin to allergens, they observed how immune responses evolved after subsequent allergen exposure.
IL-13 Activates Dendritic Cells to Drive Allergy
The study demonstrated that IL-13 does not directly stimulate antibody-producing B cells or T cells. Instead, it enhances the activity of cDC2 dendritic cells, which specialize in presenting allergens to other immune cells.
This "licensing" process enables dendritic cells to trigger the production of high-affinity immunoglobulin E (IgE) antibodies, the antibodies primarily responsible for allergic reactions and anaphylaxis.
Researchers identified a specific population of cDC2 cells expressing IL13RA1, CX3CR1, and CD301b that plays a central role in this process.
Immune Cell Migration Found Essential
The team also discovered that CX3CR1-positive cDC2 cells circulate through the bloodstream, transporting allergens from the skin to secondary lymphoid organs such as the spleen, where stronger immune responses are generated.
When researchers blocked the CX3CR1 receptor in experimental models, these dendritic cells were unable to migrate efficiently. As a result, the production of high-affinity IgE antibodies declined significantly, preventing the progression from localized skin sensitization to systemic allergic responses.
These findings suggest that targeting the CX3CR1 pathway may offer a novel therapeutic strategy to interrupt the atopic march before severe allergic disease develops.
Human Samples Support the Findings
To determine whether the same mechanism exists in people, the researchers analyzed samples from patients with atopic dermatitis and other allergic diseases.
They found significantly increased numbers of IL13RA1-positive and CX3CR1-positive cDC2 cells in both skin and blood samples. Higher levels of these immune cells were also associated with elevated IgE antibody levels, indicating that the pathway identified in mice is likely active in human allergic disease as well.
Explaining Why IL-13 Therapies Work
The research also provides a new explanation for the effectiveness of IL-13-targeting biologic drugs already used to treat atopic dermatitis, including tralokinumab and lebrikizumab.
Previous studies established that another cytokine, IL-4, directly instructs B cells to produce IgE antibodies. In contrast, this study shows that IL-13 indirectly promotes allergy by activating dendritic cells, which then orchestrate the immune response leading to high-affinity IgE production.
This distinction offers valuable insight into how existing therapies reduce allergic inflammation and suggests that disrupting the IL-13–cDC2–CX3CR1 signaling pathway could provide an even more targeted approach to preventing allergic disease progression.
Potential Impact on Future Allergy Treatments
With the global prevalence of eczema, asthma, food allergies, and other allergic disorders continuing to rise, the discovery provides important mechanistic insight into how localized allergic inflammation evolves into systemic disease.
Researchers believe that therapies designed to block dendritic cell licensing or inhibit CX3CR1-mediated immune cell migration could help prevent severe allergic reactions and interrupt the atopic march, offering new treatment possibilities for patients at risk of developing life-threatening allergies.
