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J Biophotonics. 2018 Aug;11(8):e201700282. doi: 10.1002/jbio.201700282. Epub 2018 Feb 12.

Aging of lymphoid organs: Can photobiomodulation reverse age-associated thymic involution via stimulation of extrapineal melatonin synthesis and bone marrow stem cells?

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Department of Biomedical Engineering, Chinese University of Hong Kong, Hong Kong, Hong Kong.
Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts.
Department of Dermatology, Harvard Medical School, Boston, Massachusetts.
Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts.


Thymic atrophy and the subsequent reduction in T-cell production are the most noticeable age-related changes affecting lymphoid organs in the immune system. In fact, thymic involution has been described as "programmed aging." New therapeutic approaches, such as photobiomodulation (PBM), may reduce or reverse these changes. PBM (also known as low-level laser therapy) involves the delivery of non-thermal levels of red or near-infrared light that are absorbed by mitochondrial chromophores, in order to prevent tissue death and stimulate healing and regeneration. PBM may reverse or prevent thymic involution due to its ability to induce extrapineal melatonin biosynthesis via cyclic adenosine monophosphate (AMP) or NF-kB activation, or alternatively by stimulating bone marrow stem cells that can regenerate the thymus. This perspective puts forward a hypothesis that PBM can alter thymic involution, improve immune functioning in aged people and even extend lifespan.


age-related thymic involution; bone marrow stem cells; extrapineal melatonin biosynthesis; low-level laser therapy; photobiomodulation; signaling pathways; thymus regeneration

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