A bit about those marvelous T helper cells.
The overall task of a T-cell is to respond to markers, called antigens, left behind by invaders, which stick to cells in our body. T-cells have a port, or receptor, that matches to an antigen. When that happens, the T-cell turns into either a chemical weapon or an alarm bell.
Much, much more here: advancingthescience.mayo.ed...
Jackie