PER1 and inflammatory bowel disease: PER1, one of the key characteristic circadian oscillators,[51] has been recognized previously for its role in the cell cycle and its anti‐tumor effect.[52] Biopsy analysis of inflamed tissue of IBD patients showed that Per1 levels were significantly decreased compared to the healthy control,[53] but PER1 was up‐regulated in peripheral blood of MS patients.[54] To date, there is limited literature addressing the role of PER1 in CD4+ T cells.