Cells that destroy tumours and viral infections also play a major role in reducing gut inflammation, it has emerged.
The discovery by Cork scientists opens up the possibility of new treatments for several diseases.
Killer cells are a type of white blood cell that protect the body against the tumours or viral infection.
When a tumour or virus is identified, a vanguard of immune cells accumulates to attack the invader, causing inflammation.
Scientists at the Alimentary Pharmabiotic Centre in UCC had predicted that mice lacking killer cells would develop less inflammation.
However, they were surprised when the mice developed acute inflammation and severe signs of disease. Lead investigator, Lindsay Hall said it was an exciting discovery in natural killer cell biology.
"Our findings open up the possibility of new therapeutic approaches for inflammatory bowel disease and other inflammatory diseases such as cystic fibrosis, rheumatoid arthritis and severe asthma," she said.
The study, funded by Science Foundation Ireland, made the front cover of the nature Mucosal Immunology journal.