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Innate lymphoid cells have a clear role in rheumatic disease and its related inflammatory process.
Innate lymphoid cells have a clear role in rheumatic disease and its related inflammatory process.
Mark Wenink and fellow researchers in the Netherlands present an update on the role of innate lymphoid cells in the pathogenesis of rheumatic disease, but also point out in a recent Arthritis & Rheumatology article that innate lymphoid cells play an important part in tissue homeostasis.
The balance between tissue homeostasis and inflammation and the role of innate lymphoid cells in both has been well demonstrated in skin and gut disease. However, descriptions of innate lymphoid cells contribution to rheumatic disease are lacking.
Innate Lymphoid Cells and T Cells
Although innate lymphoid cells and T cells share many characteristics, there are important differences.
T cells are primed by recognizing major histocompatibility complex II antigens presented by dendritic cells
Innate lymphoid cells do not express antigen receptors that recognize major histocompatibility complexes, but instead are activated by a wide range of chemical and molecular mediators.
T cells must be mobilized to the periphery to act at tissue barriers.
Innate lymphoid cells are always present and ready to be first responders in the immune response.
Natural killer cells are considered innate lymphoid cells, however, they are the only kind that directly induce cytotoxicity. Innate lymphoid cells that are not cytotoxic are called helper like cells.
Innate lymphoid cell development
By means of various transcription factors, helper like innate lymphoid cells develop from a common precursor cell line.
Human CD34+ cells give rise to innate lymphoid cells under specific conditions but much of the evidence concerning innate lymphoid cell development comes from animal models.
Innate lymphoid cell subsets
Classification of innate lymphoid cells is based on their developmental pathways.
1) Innate lymphoid cells type 1 (ILC1s)
2) Innate lymphoid cells type 2 (ILC2s)
3) Innate lymphoid cells type 3 (ILC3s)
4) Plasticity
Innate lymphoid cells: Psoriasis and inflammatory bowel disease
1) Psoriasis
2) Inflammatory bowel disease
The different functional properties of innate lymphoid cells in psoriasis versus inflammatory bowel disease highlights the fact that whether these cells are pathogenic or protective is highly dependent on the environment and tissue in which they are located.
Evidence of innate lymphoid cells in other rheumatic diseases
1) Psoriatic arthritis
2) Ankylosing spondylitis
3) Rheumatoid arthritis
4) Sjogren’s syndrome
5) Systemic lupus erythematosus
6) Scleroderma and Systemic Sclerosis
Take Home Points for Physicians
Innate lymphoid cells clearly play a role in rheumatic/inflammatory disease states.
Innate lymphoid cells also are essential to provide a normal state of tissue homeostasis.
The exact mechanisms by which innate lymphoid cells support inflammation are complicated and more research in humans is needed.
Understanding the role of innate lymphoid cells and ultimately targeting their development, plasticity and effector functions may lead to new therapies for patients.
Mark H. Wenink, Emmerik F. A. Leijten, Tom Cupedo and Timothy R. D. J. Radstake. “Innate Lymphoid Cells Sparking Inflammatory Rheumatic Disease?”Arthritis & Rheumatology. Vol. 69, No. 5, May 2017, pp 885–897â¨DOI 10.1002/art.40068