STANFORD, Calif. – Researchers at Stanford University are saying decades-old beliefs about how our immune system avoids attacking our own healthy tissue may be wrong.

Their study on self-reactive immune cells has revealed vast numbers of these cells remain in circulation well into adulthood, instead of dying-off in childhood.

Findings were published May 19 in the journal Immunity.

The study looked at T cells known as cytotoxic T cells, or “killer T cells,” which are particularly adept at attacking cells harboring viruses or showing signs of being or becoming cancerous, and asks the question: Why don’t they attack healthy tissue?
Work with mice has indicated that self-specific T cells are efficiently wiped out in the thymus and that as T cells mature some process within the thymus singles out self-targeting T cells and marks them for destruction.

However, researchers now know those T calls are not efficiently removed.

To test their theory, researchers exposed human blood donor T cells to some “self” antigens, as well as several viral antigens.

They were able to identify and count T cells targeting each of these antigens. What they found was the frequency of killer T cells recognizing self-antigens was almost equal to that of those recognizing foreign antigens.

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