There is support for
both hypotheses and both may contribute to the paradox of thymic selection.
Positive and Negative Selection
Hint: T cells can distinguish survival signals and negative selection signals.
What is currently the best explanation for what determines whether a T cell develops into a CD8
cell or a CD4
CD4/TCR coengagement suppresses CD8 expression, and CD8/TCR coengagement suppresses
T cells randomly down-regulate CD4 or CD8, and only cells that still bind the appropriate MHC
will get a strong enough signal to survive.
CD4 or CD8 expression is determined by the strength and duration of the TCR/MHC interaction.
CD4 or CD8 expression is predestined in the bone marrow.
T cells express CD8.
Hint: The kinetic model has the greatest experimental support.
Which of the following BEST describes the relationship between natural T
s and induced T
s differentiate into induced T
s in response to stimulation through the TCR.
s are derived from memory T cells, and induced T
s differentiate directly from
s develop in the thymus, and induced T
s develop in the periphery.