Sydney, Aug 21 (IANS): Australian researchers have discovered that the immune system is defective in people suffering from irritable bowel syndrome and this renders pain treatment ineffective in such people.

The gut contains specialised immune cells known as monocytes and macrophages.

"Our research has shown that in healthy people, these immune cells normally secrete opioid chemicals like morphine that block pain. But in people with IBS, the opioid production by these cells is defective," said lead author Patrick Hughes from school of medicine at University of Adelaide.

The research involved samples from over 100 people, half of them healthy and half suffering from IBS.

The research could also help to explain why some painkillers may not offer satisfactory relief to sufferers.

There are different forms of IBS but all of them involve unexplained gut pain which often has the greatest impact on sufferers' quality of life.

The exact cause of pain in IBS sufferers remains unknown "but we have now confirmed, and detailed, information about the important role of the immune system in this pain response," Hughes noted.

The findings were published in the journal Brain, Behavior and Immunity.