T-helper cell:
Immune cells that are triggered by antibodies to seek and attack invading organisms. Cells called macrophanges summon T-helper cells to the site of the infection and present a protruding antigen onto which the T-helper cell locks, thus "recognizing" the invading substance. The T4-helper 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. T-helper cells are also called T4 cells and are normally twice as common as T8 cells. If a person has AIDS, the proportion of T4 to T8 cells is often reversed.
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