When we’re healthy, T cells keep the immune cells in the meninges from inflaming the brain. But when we get sick, the T cells loosen their hold to let the immune system attack invading pathogens. The resulting inflammation helps clear out the invaders, but it also blunts learning. When we’re sick, Kipnis proposes, it’s more important to launch a powerful immune attack than to have a sharp mind. “Everything in life is priorities,” he says.
Kipnis has recently started to investigate what happens to people’s brains when they start losing T cells. People with cancer, for example, often suffer a loss of T cells when they undergo chemotherapy. It may be no coincidence, he argues, that chemotherapy is notorious for causing “chemo brain”—a fuzzy mental state in which patients have trouble thinking clearly. Kipnis proposes that without T cells to keep inflammation in check, immune cells in the meninges pump harmful compounds into the brain.
Why this research matters:
Drugs that might be able to rework neurons inside the brain and improve mental sharpness are often too big to get past the blood-brain barrier, for example. Dopamine, a molecule crucial for signaling between neurons, cannot cross this barrier, which is why its chemical precursor, L-dopa, is used instead to treat Parkinson’s disease. But the immune system offers a new way of changing our cognition and treating illnesses affecting the brain.