A type of immune system cell plays a key role in the development of type-2 diabetes, research suggests.
Neutrophils, which normally attack bacteria and other foreign invaders, also secrete a protein that promotes insulin resistance, scientists found.
The condition, which occurs when the body stops responding to the blood sugar-regulating hormone insulin, is one of the main features of type-2 diabetes.
Neutrophils appear to promote chronic low-grade inflammation, increasing the chances of insulin resistance.
"These results are largely unexpected," said US researcher Dr Da Young Oh, of the University of California at San Diego, US.
"Although several immune cells have been established in the aetiology (origin) of insulin resistance, the role of neutrophils in this process has remained unclear until now."
Neutrophils could be a new target for drugs developed to treat insulin resistance, say the scientists writing in the journal Nature Medicine.
The enzyme secreted by neutrophils, called neutrophil elastase (NE), impairs insulin signalling.
Removing NE from obese mice fed a high-fat diet improved their insulin sensitivity, the study showed.
"Given that NE mediates insulin resistance, one could, in theory, take an NE activity inhibitory approach to reverse or improve insulin resistance," said Dr Oh.