A subtype of T-lymphocytes which cooperate with B-lymphocytes for the synthesis of antibody to many antigens; they play an integral role in immunoregulation.

A subclass of T-cells responsible for stimulating other T-cells and B-cells.

An important part of the IMMUNE SYSTEM. HELPER T-CELLS are what your body uses to identify germs. When HIV finds a HELPER T-CELL it sneaks inside the cell and forces the cell to make more HIV. After a while many copies of HIV burst out of the cell, killing it. The new copies of HIV go find more HELPER T-CELLS. Eventually, HIV starts killing HELPER T-CELLS faster than your body can make them. This is how someone gets AIDS. Without HELPER T-CELLS, all kinds of germs that your body could normally fight off can grow and multiply, and make you very sick or even dead.

T-lymphocyte bearing the CD4+ cell surface marker. Helper T-cells are the chief regulatory cells of the immune system, controlling activities such as turning antibody production on and off. They are the main targets of HIV infection. (See CD4+ T-lymphocyte.)

see CD4 cell.

A specialized white blood cell that calls upon other parts of the immune system to fight an infection or foreign material.