The other major group of lymphocytes is the T cells, ( T stands for Thymus, the body organ in which they mature).
T Cells look like B Cells under a microscope. The T cells are divided into occupations such as helper T cells, suppressor T cells, and cytotoxic T cells. These are all very specialized functions. Some T cells the (cytoxic or CD8) attack invaders and infected cells directly, while others, the helper & suppressor T’s, help regulate the immune response and keep it from becoming overactive. Cytotoxic ( or cell-killing) T cells identify foreign organisms changes in their surface proteins. They work with the suppressor and helper T cells, which regulate the activity of the cytotoxic T cells.
Suppressor T cells help to regulate the immune reaction by preventing cytoxic T cells from killing healthy cells. Helper, or CD4, T cells help cytoxic cells kill infected cells. You may have heard of CD4 cells in the context of HIV infection, because these are the cells targeted by the HIV. Low levels of CD4 cells signal a serious HIV infection.
One of the reasons viruses are so dangerous is that they don’t just cruise around the tissue or blood and hide there, waiting for your body to destroy them. They actually creep inside your cells, and that means your body has to destroy some of its own cells if they become infected.
Once inside your cells, a virus messes with your DNA, tricking your cells into reproducing the virus by mingling its own DNA with yours. Then the virus uses your cells’ DNA-processing system to replicate its own DNA too.
When a cell becomes infected with a virus in this way, the situation stats to resemble the scene fom the science-fiction movie Alien. The only way to prevent the dangerous alien that is a virus from reproducing is to kill the newly infected cell. That where’s the killer T cells come in. Natural killer cells sense a distress signal from the cells infected by a virus.
Natural killer cells are involved in many search and destroy missions for our immune system. They’re important in killing cancerous cells that crop up in our bodies, before they can grow into tumors. Cancer in the human body is not as rare as most people think. But for a number of reasons, most of these cells are never allowed to grow into tumors capable of killing us.