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The thymus atrophies as age progresses. Does the T cell selection (which happens in the thymus) continue to take place? This doubt came into my mind because in the cadaver we dissected, the thymus was hardly more than scanty fibrous tissue. This definitely should have some effect on immune tolerance right? Is this the reason why the elderly are more prone to autoimmune diseases?

Or is it that selection happens only in children? This line of thought would pose a problem since T-cells are short lived and they continuously need to be produced. Or is it that the site of selection is shifted to some other place?

P.S. I am asking these questions assuming that selection is necessary every time new T cells are made. Correct me if this primary assumption is wrong.

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T cells have a long half life (both naive and memory cells have halflives measured in years), especially when taking into account the fact that memory cells in particular can slowly proliferate and renew themselves. An adult human therefore has 20-50 years' worth of accumulated T cells by the time they grow old, and those include both memory cells and naive cells that are potentially able to recognize new antigens. The thymus does continue to produce some new cells at a slow rate, but the backlog of previously produced cells are also able to monitor for pathogens.

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  • $\begingroup$ Thanks! Just thought memory cells have long half live, dint know about the naive cells also being similar. So hematopoiesis in later stages of life wouldn't include T cell synthesis? or rather a decilne. Does creation of new leukocutes majorly mean, new non-lymphocytes? $\endgroup$ – Polisetty Mar 8 '16 at 20:34
  • $\begingroup$ @Polisetty if you have a new question, please ask. $\endgroup$ – MattDMo Mar 9 '16 at 2:07
  • $\begingroup$ @mattDMo the question is related to the answer he's given. Was just clarifying. I'll post if the answer doesn't turn up here :) $\endgroup$ – Polisetty Mar 9 '16 at 6:59

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