Using a stem cell model, they showed how immune cells attacked dopamine-producing cells derived from people with Parkinson's disease but not from people without it.

Dopamine is a chemical messenger that supports many important brain functions. These include functions that deal with reward, emotions, pleasure, and movement control.

In Parkinson's disease, the midbrain neurons, or brain cells, that make dopamine die off. But it is not clear what causes their death.

As more and more dopamine cells die, levels of the chemical messenger drop, giving rise to symptoms such as tremor, slowness, rigidity, and problems with balance. Problems with speech and swallowing also develop, as do several nonmovement symptoms.

Estimates suggest that around half a million people in the United States have Parkinson's disease.

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