According to the new study, one reason might be that the genes that set the body clock are intimately connected to certain immune cells, Stuff.co.nz reported.
Lora Hooper, immunologist at the University of Texas Southwestern Medical Center in Dallas claimed that the discover happened when she and her colleagues were studying NFIL3, a protein that guides the development of certain immune cells and turns on the activity of others.
The gene for this protein is mutated in some patients with inflammatory bowel disease, the study also found that the mice lacking the gene for NFIL3 had more so-called TH17 cells in their intestines.
These cells are a type of immune cell known as a T cell, which get their name from a signal they produce, called interleukin 17, which tells other T cells to increase the immune response.
The study is published online in the journal Science.