August 26, 2009

Immune system plays role in bone loss

U.S. researchers say immune system-based approaches may help in treating osteoporosis.

The study, published in Clinical Immunology, links bone loss to the immune system's reaction to cholesterol-related oxidation -- cell and tissue damage from exposure to free radicals. The scientists came to their conclusion by observing human T cells exposed in the laboratory to oxidized low-density lipoprotein, the bad cholesterol.

Both the resting and the activated T cells started churning out a chemical that stimulates cells whose sole purpose is to destroy bone, study leader Rita Effros of the David Geffen School of Medicine at the University of California, Los Angeles, said in a statement.

These results were repeated in an animal study comparing mice fed a high-fat diet to those eating a standard diet. After 11 months, the mice given food high in fat not only showed elevated cholesterol and thinner bones, but their T cells switched on a gene that produced a chemical called RANKL.

It's normal for our T cells to produce small amounts of RANKL during an immune response, Effros said in a statement. But when RANKL is manufactured for long periods or at the wrong time, it results in excessive bone damage.