Protein Linked to Transplant Rejection

NEW YORK — Scientists have identified a protein fragment that makes female mice reject tissue transplanted from males, a possible step toward improving human transplants.

The fragment appears on male tissue. It is the first to be identified out of perhaps a half-dozen such male markers in mice and people, said researcher Elizabeth Simpson at the Medical Research Council Clinical Sciences Center in London.

In humans, the male-linked protein fragments belong to a class of markers that play a relatively minor role in organ rejection when recognized by the recipient’s immune system, Simpson said.

If more members of this class can be identified, researchers might be able to find ways to make the immune system ignore them, she said.

The main impact would come in bone-marrow transplants, where the research might reduce the risk that the transplanted marrow would attack the recipient’s body, a potentially deadly process called graft-versus-host disease, she said.

In transplants of kidneys, livers and other organs, drugs that suppress the immune system now effectively control the risk from the protein markers, she said.

She and colleagues report the mouse work in the Aug. 24 issue of the journal Nature.