The pathological role and targeted therapy research progress of IL-6 signaling pathway in immune inflammatory skin diseases

Interleukin-6 (IL-6) is a multifunctional cytokine composed of 174 amino acids, with a molecular weight of approximately 21-28 kDa, and is a typical representative of the IL-6 family of cytokines.

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The Pathological Role of IL-6 Signaling Pathway in Immunoinflammatory Skin Diseases and Advances in Targeted Therapy

1. Biological Characteristics of IL-6 and Its Signal Transduction Mechanisms

Interleukin-6 (IL-6) is a multifunctional cytokine composed of 174 amino acids with a molecular weight of approximately 21-28 kDa, serving as a typical representative of the IL-6 family of cytokines. IL-6 exerts its biological effects through two distinct signal transduction mechanisms:

Classical signaling pathway: IL-6 first binds to the membrane-bound IL-6 receptor (mIL-6R) to form a complex, which then interacts with transmembrane glycoprotein gp130 (CD130) dimers, activating downstream signaling pathways such as JAK/STAT, MAPK, and PI3K/AKT. Notably, the expression of mIL-6R is primarily restricted to specific cell types, including hepatocytes, certain leukocyte subsets, and macrophages.

Trans-signaling pathway: Soluble IL-6 receptor (sIL-6R) binds to IL-6 and activates cells widely expressing gp130, significantly expanding the range of IL-6 biological activity.

Functionally, IL-6 exhibits extremely diverse biological activities in the body:

In the acute-phase response, it stimulates hepatocytes to produce acute-phase proteins such as C-reactive protein (CRP), serum amyloid A (SAA), and fibrinogen.

In immune regulation, IL-6 promotes the differentiation of B cells into plasma cells, modulates the Th17/Treg balance, and influences macrophage polarization.

In the hematopoietic system, it participates in the maintenance and differentiation of hematopoietic stem cells.

In metabolism, it affects lipid metabolism and insulin sensitivity.

Additionally, it is involved in bone metabolism balance, angiogenesis, and tissue repair.

This broad functional spectrum makes IL-6 a key regulatory molecule linking innate and adaptive immunity.

2. The Role of IL-6 in Skin Pathophysiological Processes

In skin biology, IL-6 participates in skin inflammatory responses and tissue remodeling through multiple mechanisms. Keratinocytes, fibroblasts, melanocytes, endothelial cells, and skin-resident immune cells (such as Langerhans cells, mast cells, and γδ T cells) can all produce IL-6. When the skin is exposed to external stimuli or undergoes pathological changes, these cells secrete large amounts of IL-6, acting on surrounding cells through autocrine and paracrine mechanisms.

In inflammatory skin diseases, abnormal IL-6 expression is closely associated with various pathological processes:

Pro-inflammatory effects: IL-6 induces vascular endothelial cells to express adhesion molecules (e.g., ICAM-1, VCAM-1), promoting leukocyte recruitment to inflammatory sites; it also stimulates the production of multiple pro-inflammatory cytokines (e.g., IL-1β, TNF-α) and chemokines, amplifying the inflammatory response.

Impact on barrier function: IL-6 inhibits the expression of keratinocyte differentiation-related proteins (e.g., loricrin, filaggrin), disrupting skin barrier integrity.

Involvement in fibrosis: In fibrotic skin diseases such as systemic sclerosis, IL-6 activates fibroblasts, promoting collagen synthesis and extracellular matrix deposition.

Regulation of autoimmunity: IL-6 promotes the differentiation of autoreactive B cells into plasma cells, increasing autoantibody production; it also disrupts immune tolerance by affecting the Treg/Th17 balance.

Clinical studies have shown that IL-6 levels in serum and skin lesions are significantly elevated in patients with various inflammatory skin diseases, positively correlating with disease activity. For example, serum IL-6 levels in systemic sclerosis patients correlate with the modified Rodnan skin score (mRSS) and the degree of pulmonary fibrosis; serum IL-6 levels can rise sharply during disease flares in adult Still’s disease; and IL-6 expression increases in active lesions of Behçet’s disease.

3. Therapeutic Strategies Targeting IL-6/IL-6R and Their Mechanisms of Action

Targeted therapies for the IL-6 signaling pathway are mainly divided into three categories: anti-IL-6 monoclonal antibodies, anti-IL-6R monoclonal antibodies, and soluble gp130Fc fusion proteins. Currently, IL-6R inhibitors approved for clinical use by the FDA include tocilizumab, sarilumab, and satralizumab.

These biological agents exert therapeutic effects through the following mechanisms:

Blocking signal transduction: Specifically binding to IL-6 or IL-6R to prevent the formation of the IL-6/IL-6R/gp130 complex, inhibiting downstream signaling pathway activation.

Regulating immune cell function: Reducing autoantibody production, modulating the Th17/Treg balance, and suppressing pathological immune responses.

Alleviating inflammatory responses: Decreasing the levels of acute-phase proteins such as CRP and SAA, and reducing the production of pro-inflammatory cytokines.

Affecting tissue remodeling: In fibrotic diseases, inhibiting fibroblast activation and excessive collagen deposition.

Pharmacokinetically, these biological agents are typically administered via subcutaneous injection or intravenous infusion with long half-lives (tocilizumab: approximately 11-13 days; sarilumab: approximately 22 days), allowing dosing intervals of 1-4 weeks. Clinical application requires individualized dose adjustment based on factors such as patient weight, disease type, and activity.

4. Application of IL-6 Targeted Therapy in Specific Skin Diseases

4.1 Systemic Sclerosis (SSc)

In the pathogenesis of SSc, IL-6 participates in skin and visceral organ fibrosis by promoting fibroblast activation and collagen synthesis. Multiple clinical studies have shown that tocilizumab treatment significantly improves skin fibrosis in SSc patients. Its mechanisms may include inhibiting Th17 cell differentiation, reducing collagen production, and improving vascular endothelial function. Notably, tocilizumab is more effective in patients with early diffuse cutaneous SSc, highlighting the importance of early intervention.

4.2 Adult-Onset Still’s Disease (AOSD)

AOSD is a systemic inflammatory disease characterized by high fever, rash, arthritis, and multisystem involvement. IL-6 plays a central role in AOSD pathogenesis, with its levels closely correlating with disease activity. Clinical observations have found that tocilizumab rapidly controls systemic symptoms and skin manifestations in AOSD patients, significantly reducing glucocorticoid dosage. It shows particularly sustained efficacy in patients with chronic arthritis-type AOSD.

4.3 Behçet’s Disease (BD)

BD is a systemic vasculitis-based disease. Tocilizumab demonstrates good therapeutic effects in refractory BD, especially in patients with ocular, neurological, or vascular involvement. Its mechanisms may involve inhibiting neutrophil activation, reducing vascular endothelial damage, and regulating Th17 responses. However, tocilizumab is relatively less effective in patients with isolated mucocutaneous involvement.

4.4 Other Inflammatory Skin Diseases

Systemic Lupus Erythematosus (SLE): IL-6 participates in SLE pathogenesis by promoting autoantibody production and lupus nephritis development. Preliminary clinical studies suggest that IL-6 inhibitors may improve arthritic symptoms and serological indicators in SLE patients.

Psoriatic Arthritis (PsA): IL-6 inhibitors primarily improve joint symptoms but have limited effects on skin lesions.

Atopic Dermatitis (AD): Case reports indicate that tocilizumab may be effective in some refractory AD patients, but more evidence is needed.

5. Safety and Tolerability Considerations

Common adverse reactions of IL-6 targeted therapy include:

Infection risk: Particularly upper respiratory tract infections, pneumonia, and skin and soft tissue infections; severe cases may develop sepsis.

Gastrointestinal reactions: May increase the risk of diverticulitis and intestinal perforation.

Laboratory abnormalities: Common findings include neutropenia, thrombocytopenia, abnormal liver function, and elevated blood lipids.

Infusion reactions: Including fever, rash, and headache.

Malignancies: Long-term use may slightly increase the risk of malignancies, especially non-melanoma skin cancer.

Clinical application considerations:

Screen for latent infections such as tuberculosis and hepatitis B before treatment.

Contraindicated in patients with active infections.

Regular monitoring of blood routine, liver function, and blood lipids.

Use with caution in patients with a history of diverticulitis.

Pay attention to synergistic effects with other immunosuppressants.

6. Future Research Directions and Prospects

Although IL-6 targeted therapy shows promising prospects in some inflammatory skin diseases, several issues require further exploration:

Precision treatment strategies: Develop biomarkers to predict treatment responses and achieve individualized therapy.

Combination therapy regimens: Explore combinations with other targeted drugs (e.g., JAK inhibitors, IL-17 inhibitors).

Development of new formulations: Develop long-acting preparations, topical delivery systems, or bispecific antibodies.

Expanding indications: Validate efficacy in more skin diseases, such as scleroderma-like graft-versus-host disease and neutrophilic dermatoses.

Long-term safety assessment: Establish more comprehensive long-term follow-up data, particularly regarding infection, malignancy, and cardiovascular risks.

With deepened understanding of the IL-6 signaling pathway and the development of new targeted drugs, the role of IL-6 inhibitors in the treatment of immunoinflammatory skin diseases will further expand, bringing new therapeutic hope to more patients with refractory skin diseases.

Disclaimer: This article partially utilizes artificial intelligence assistance in its creation. If any content involves copyright or intellectual property issues, please let us know and we promise to verify and remove it as soon as possible.

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