Programmed cell death

The number of cells is tightly regulated, not simply by controlling the rate of cell division, but also by controlling the rate of cell death.

If cells are no longer needed, they commit suicide by activating an intracellular death program: programmed cell death, apoptosis.

In a healthy adult human, billions of cells die in the bone marrow and intestine every hour.

Cell death helps regulate cell numbers.

In the developing nervous system, for example, cell death adjusts the number of nerve cells to match the number of target cells that require innervation.

In all these cases, the cells die by apoptosis.

programmed cell death protein 1 (PD –1) is present on the surface of T cells and acts as a negative regulator of immune responses.

PD-1 protein is upregulated on activated immune cells and is expressed persistently on chronically activated immune cells, where its engagement leads to progressive loss of T cell functions, including T cell proliferation, and to cytokine a production: loss of these effector functions results in a reduction in antigen specific immune responses.

Blocking PD-1 reinvigorated antitumor activity.


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