Maturation of a wanna be T cell

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.

Helper T cell

Killer T cell