T4 cell:
Immune cells that are triggered by antibodies to seek and attack invading organisms. Cells called macrophanges summon T4 cells to the site of the infection and present a protruding antigen onto which the T4 cell locks, thus "recognizing" the invading substance. The T4 cell then reproduces and secretes its potent lymphokine hormones that stimulate B-cell production of antibodies; signal "natural killer" or cytotoxic (cell-killing) T-cells; and summon more macrophanges to the site of the infection. T4 cells are normally twice as common as T8 cells. If a person has AIDS, the proportion of T4 to T8 cells is often reversed. T4 cell are also called T-helper cells.
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