Also known as T lymphocytes, T cells are white blood cells that participate in a variety of cell-mediated immune reactions. Three fundamentally different types of T cells are recognized: helper, killer, and suppressor. CD4 cells are also known as T helper cells, whereas CD8 cells are one type of T killer cells. T cells are essential for a normal functioning immune system. The “T” stands for the thymus, where T-cells mature.
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