2026-01-26
What if osteoarthritis were an immune disease?
Rhumatology
By Ana Espino | Published on January 26, 2026 | 3 min read
Osteoarthritis is the most common joint disease, affecting over 300 million people worldwide. Long viewed as a simple consequence of mechanical cartilage wear, it is now recognized as a complex disorder involving mechanical, metabolic, and immune factors.
Current treatments remain symptomatic: analgesics, non-steroidal anti-inflammatory drugs, joint injections, and eventually surgery. No therapy currently slows or reverses the degenerative process. The failure of purely mechanical or conventional anti-inflammatory approaches highlights the urgent need to better understand the underlying mechanisms of the disease.
Recent data suggest that osteoarthritis progression is driven by low-grade chronic inflammation, often silent but persistent, affecting the cartilage, synovial membrane, and subchondral bone. This inflammation appears to be at least partially orchestrated by both innate and adaptive immune cells—including macrophages, lymphocytes, dendritic cells, and mast cells.
This review was therefore initiated to explore the role of the immune system in the development and progression of osteoarthritis, in order to identify new therapeutic targets beyond conventional anti-inflammatory strategies.
This review focused on the role of immune cells in osteoarthritis, based on data from animal models, histological analyses of human joint tissues, and molecular and immunophenotypic studies. The findings reveal that osteoarthritis is not merely a mechanical disorder, but involves abnormal activation of the immune system, particularly the innate immune response. Synovial macrophages, found throughout all disease stages, contribute to inflammation by producing pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α. Their polarization into M1-type macrophages is associated with worsening joint damage, while M2 macrophages (anti-inflammatory) appear protective.
Mast cells also release pro-inflammatory mediators (histamine, tryptase), promoting cartilage degradation. Dendritic cells, although few in number, can trigger localized autoimmune responses. The involvement of the adaptive immune system is more controversial. CD4+ and CD8+ T lymphocytes have been identified in osteoarthritic tissues, with pro-inflammatory behavior via Th1 and Th17 subtypes. Their activation suggests a specific immune response, possibly against neo-antigens derived from damaged cartilage.
Finally, danger-associated molecular patterns (DAMPs), released during cartilage breakdown, can activate innate immune receptors such as TLRs and NLRP3, maintaining a vicious cycle of joint inflammation.
Long viewed as a mechanical disease, osteoarthritis is now understood to involve complex immune mechanisms that contribute to inflammation and joint degradation. Yet, this immune dimension is still under-recognized in clinical practice, despite its probable role in disease progression.
This review aimed to clarify the role of the immune system, especially innate immune cells such as macrophages and mast cells, in the development of osteoarthritis. It highlights the role of low-grade, localized chronic inflammation, which may represent a new therapeutic target.
However, limitations of this study remain and justify further research. These future investigations will include large-scale clinical studies in humans, along with the development of specific immune biomarkers. In parallel, the evaluation of therapies targeting innate immune pathways represents a promising strategy to enable more refined patient stratification and the development of personalized disease-modifying treatments.
Read next:
Osteoarthritis is the most common joint disease, affecting over 300 million people worldwide. Long viewed as a simple consequence of mechanical cartilage wear, it is now recognized as a complex disorder involving mechanical, metabolic, and immune factors.
Current treatments remain symptomatic: analgesics, non-steroidal anti-inflammatory drugs, joint injections, and eventually surgery. No therapy currently slows or reverses the degenerative process. The failure of purely mechanical or conventional anti-inflammatory approaches highlights the urgent need to better understand the underlying mechanisms of the disease.
Recent data suggest that osteoarthritis progression is driven by low-grade chronic inflammation, often silent but persistent, affecting the cartilage, synovial membrane, and subchondral bone. This inflammation appears to be at least partially orchestrated by both innate and adaptive immune cells—including macrophages, lymphocytes, dendritic cells, and mast cells.
This review was therefore initiated to explore the role of the immune system in the development and progression of osteoarthritis, in order to identify new therapeutic targets beyond conventional anti-inflammatory strategies.
Articular inflammation: who’s really in charge?
This review focused on the role of immune cells in osteoarthritis, based on data from animal models, histological analyses of human joint tissues, and molecular and immunophenotypic studies. The findings reveal that osteoarthritis is not merely a mechanical disorder, but involves abnormal activation of the immune system, particularly the innate immune response. Synovial macrophages, found throughout all disease stages, contribute to inflammation by producing pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α. Their polarization into M1-type macrophages is associated with worsening joint damage, while M2 macrophages (anti-inflammatory) appear protective.
Mast cells also release pro-inflammatory mediators (histamine, tryptase), promoting cartilage degradation. Dendritic cells, although few in number, can trigger localized autoimmune responses. The involvement of the adaptive immune system is more controversial. CD4+ and CD8+ T lymphocytes have been identified in osteoarthritic tissues, with pro-inflammatory behavior via Th1 and Th17 subtypes. Their activation suggests a specific immune response, possibly against neo-antigens derived from damaged cartilage.
Finally, danger-associated molecular patterns (DAMPs), released during cartilage breakdown, can activate innate immune receptors such as TLRs and NLRP3, maintaining a vicious cycle of joint inflammation.
Shifting the paradigm: treating immunity, not wear
Long viewed as a mechanical disease, osteoarthritis is now understood to involve complex immune mechanisms that contribute to inflammation and joint degradation. Yet, this immune dimension is still under-recognized in clinical practice, despite its probable role in disease progression.
This review aimed to clarify the role of the immune system, especially innate immune cells such as macrophages and mast cells, in the development of osteoarthritis. It highlights the role of low-grade, localized chronic inflammation, which may represent a new therapeutic target.
However, limitations of this study remain and justify further research. These future investigations will include large-scale clinical studies in humans, along with the development of specific immune biomarkers. In parallel, the evaluation of therapies targeting innate immune pathways represents a promising strategy to enable more refined patient stratification and the development of personalized disease-modifying treatments.
Read next:
About the author – Ana Espino
As a scientific writer, Ana is passionate about bridging the gap between research and real-world impact. With expertise in immunology, virology, oncology, and clinical studies, she makes complex science clear and accessible. Her mission: to accelerate knowledge sharing and empower evidence-based decisions through impactful communication.
PhD in Immunology, specialized in Virology
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