Some people with auto­immune diseases also suffer from depression, mood disorders and cognitive impairment. This happens when certain autoantibodies cross the blood-brain barrier, the body’s natural blocking mechanism for protecting the brain, and attach themselves to specific receptors on brain chemicals that carry information between brain cells.

In healthy people, the blood-brain barrier functions as a series of “tight junctions’’ between the cells lining the brain’s blood vessels “so there is no place for the molecules to scoot through,” says Betty Diamond, director of the Center for Autoimmune and Musculoskeletal Diseases at the Feinstein Institute for Medical Research. With autoimmune diseases, however, “inflammation and stress can loosen these junctions,” she says.

There also is evidence suggesting that women with autoimmune diseases have an increased risk of giving birth to children with an autism spectrum disorder. This is probably because of maternal autoantibodies that cross the fetus’s blood-brain barrier, Diamond says. “A developing fetus doesn’t have a mature blood-brain barrier, and the fetus is bathed in maternal antibodies,” she says, adding: “We need to learn more about what regulates the blood-brain barrier” both in women and in fetuses.

One approach researchers are exploring is using some kind of decoy, possibly a drug, that “could sponge up the offending auto­antibodies, keeping them from attacking,” Diamond says, or, alternatively, a medication that could keep the junctions tight enough to prevent autoantibodies from entering the brain.