Liver 'kills immune cells'

An international team, led by the University of Sydney, says it has for the first time seen in mice how the liver goes independent, engulfing and destroying body's defence troops -- T-cells.

'In 2004, we discovered that healthy liver cells can engulf active immune cells, known as T-cells and now we've seen that those T-cells are actually destroyed,' Dr Patrick Bertolino, who led the team, said.

He added: 'The liver is an amazing organ. Most people think it just breaks down alcohol, but it's the factory of the body -- breaking down substances we don't want and making  the ones that we do. We now know liver cells also have the ability to subvert the orders of the immune system. Our discovery might explain why liver transplants have lower rejection rates than other organ transplants.'

In their research, the scientists proved found healthy mouse liver cells eating T-cells, which was unexpected as this 'cell cannibalism' had only previously been seen in tumour cells.

One potential benefit of the research is reducing rejection in organ transplants, say the scientists. In transplantations, the new organ is seen by the body as a foreign object: the spleen or lymph nodes tell naive T-cells to replicate and turn into killer T-cells, which are sent off to invade and kill the 'foreign' cells.

What the scientists have discovered is the liver goes around this process -- liver cells signal to naive T-cells and digest them before they have a chance to become killer T-cells.

Team member Geoff McCaughan said the cocktail of immunosuppressive drugs that organ transplant patients receive reduce the odds of organ rejection but makes patients' immune systems weak, leaving them open to serious infection from otherwise minor illnesses like cold or flu.

These drugs also predispose the patient to long term heart disease and cancer. 'If we can harness the way the liver controls T-cells, then longterm there is a chance that transplant patients won't need these drugs,' he said. The findings have been published in the 'Proceedings of the National Academy of Sciences' journal.