Skin `makes out good bacteria`

Washington: There are more bacteria living on our skin and in our gut than cells in our body. But, it was not clear how the immune system could tell that these bacteria are harmless.

Now, an international team, led by Centenary Institute in Sydney, claims to have discovered a set of peacekeepers-immune cells in outer layers of skin that stop people from attacking friendly bacteria.

The work will open the way to new therapeutic options for immune-mediated disease such as inflammatory bowel disease, say scientists.

In their research, the team, led by Prof Barbara Fazekas de St Groth, has shown the immune cells in the outer layer of the skin constantly act as peacekeepers to stop the immune system from reacting the way it normally would.

Known as Langerhans cells, they resisted every attempt by the scientists to get them to generate an immune response.

They worked with a group of mice in which only the Langerhans cells could stimulate the immune system. They then activated the Langerhans cells and measured the response.

"No matter what we threw at them to get them to activate a long-term immune response, Langerhans cells always induced immune tolerance," Prof Fazekas said.

This result seems to go against the prevailing wisdom in immunology about the workings of dendritic cells, the class of immune cell to which Langerhans cells belong, according to the scientists.

The findings have been published in the `Proceedings of the National Academy of Sciences` journal.


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