When you are a kid at home, you wanna be something, but you don't know what. You are at the pro-something stage of your life. You could be a pro-science or a pro-arts.
Similarly, in the
bone marrow,
pro T cells know they wanna be a T cell but they don't know which one. Pro T cells are double negative, that is,
CD4 -ve and CD8 -ve.
|
Pro T cell
|
When you go to school, you wanna become everything! You wanna be a doctor and a singer and they have nothing in common. Your parents tell you that you are being immature, that you should choose one. But you dream on being both =)
Similarly, when T cells enter the
thymus, they are double positive, that is,
CD4 +ve and CD8 +ve. They are known as the
immature T cells. The thymic cortex is where you'd find them.
|
Immature T cell |
You go through
school and college, like and dislike things and finally
decide on one. That is when you become
mature.
Similarly, T cells go through the
thymic cortex and medulla, have their positive and negative selection, and decide
whether they are CD4 +ve or CD8 +ve. At this stage, they are called
mature T cells.
|
Helper T cell |
|
Cytotoxic T cell |
Then you finally pursue your dream, reside in your home and be useful when needed.
Similarly,
T cells live in the Periarteriolar lymphoid sheaths, and come to the rescue when they are presented with blood borne antigens via myeloid dendritic cells.
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