Magazine article Science News

Slipping Past the Immune Centurions

Magazine article Science News

Slipping Past the Immune Centurions

Article excerpt

The cells of the immune system, like gallant warriors, protect the body from foreign invaders. Yet these cells appear to grant a special privilege to some tissues. Testes, eyes, and even the brain appear to slip quietly past the body's guardians.

These immune-privileged tissues can be transplanted from one individual to another without rejection, even among unrelated donors and recipients. Conversely, the immune system permits other tissues to be transplanted into these privileged sites.

Now, a study indicates that privileged tissues may not have been granted free rein by the immune system's lymphocytes after all. Instead, the tissues appear to produce a molecule, known as Fas ligand, that kills immune cells approaching with destructive intent. This finding could someday improve transplantation outcomes and mediate self-destructive autoimmune diseases.

"This is a highly specific immune suppression," says study author Richard C. Duke of the University of Colorado School of Medicine in Denver. "And if the cells [of a transplanted organ] express Fas ligand, it is protected from the immune system."

When lymphocytes become activated during an immune response, whether to a virus, bacterium, or transplanted organ, they manufacture a large number of molecules known as Fas and imbed them into their cell surfaces. When these Fas molecules encounter a Fas ligand on another lymphocyte, it triggers a process called apoptosis, which leads the Fas-carrying lymphocytes to commit suicide. …

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