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Int J Tryptophan Res. 2017 Jun 14;10:1178646917713491. doi: 10.1177/1178646917713491. eCollection 2017.

Aspects of Tryptophan and Nicotinamide Adenine Dinucleotide in Immunity: A New Twist in an Old Tale.

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Department of Cardiovascular Surgery, University Hospital Zurich, Zurich, Switzerland.
Angiogenesis and Brain Development Laboratory, Division of Basic Neuroscience, McLean Hospital and Harvard Medical School, Belmont, MA, USA.
Division of Transplant Surgery and Transplantation Surgery Research Laboratory, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.


Increasing evidence underscores the interesting ability of tryptophan to regulate immune responses. However, the exact mechanisms of tryptophan's immune regulation remain to be determined. Tryptophan catabolism via the kynurenine pathway is known to play an important role in tryptophan's involvement in immune responses. Interestingly, quinolinic acid, which is a neurotoxic catabolite of the kynurenine pathway, is the major pathway for the de novo synthesis of nicotinamide adenine dinucleotide (NAD+). Recent studies have shown that NAD+, a natural coenzyme found in all living cells, regulates immune responses and creates homeostasis via a novel signaling pathway. More importantly, the immunoregulatory properties of NAD+ are strongly related to the overexpression of tryptophan hydroxylase 1 (Tph1). This review provides recent knowledge of tryptophan and NAD+ and their specific and intriguing roles in the immune system. Furthermore, it focuses on the mechanisms by which tryptophan regulates NAD+ synthesis as well as innate and adaptive immune responses.


NAD+; Nicotinamide adenine dinucleotide; immune responses; kynurenine pathway; tryptophan

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DECLARATION OF CONFLICTING INTERESTS: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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