"It's too late for these cells to join the major glands; eventually some decide to become thymus cells, and this is where cervical thymi come from," said Manley.
Some of these cells turn directly into thymus cells. Others, for reasons not yet fully understood, appear to start out as parathyroid cells, but unexpectedly switch and turn into thymus cells instead.
The ultimate question facing researchers now is whether these satellite thymus glands matter. Are they merely an inconsequential relic of an untidy developmental process? If not, do they help or harm the body?
Manley cautions that it is too early to answer these questions definitively, but the group examined T-cells created by both the direct developing thymi and those derived from parathyroid cells. They discovered that they have very different functions from those found in the main thymus gland.
The thymus cells that began life as parathyroid primarily make a kind of T-cell that is thought to act as an early responder to pathogens in the body.
"They're kind of like the canary in a coal mine," Manley said. "They see something harmful and alert other cells to the problem so they can come and fight the infection."
Cells of this type are relatively rare in the body, but some research suggests that more of them could help the body fight infections more rapidly and completely.
However, both the direct developing and parathyroid-derived thymus cells can also produce autoreactive T-cells.
Just like their helpful cousins, these cells go out and destroy other cells in the body, but they lack the ability to distinguish between normal healthy cells and pathogenic cells like bacteria. Too many of these T-cells can lead to serious autoimmune diseases, such as multiple sclerosis, rheumatoid arthritis and Type 1 diabetes.
Nobody can say
|Contact: Nancy Manley|
University of Georgia