Lymphocytes have evolved to provide a more versatile means of defense. These cells display on their cell surface receptors that recognize specific antigens. When activated, the cells enlarge to form lymphoblasts and then proliferate and differentiate into an antigen-specific effector cell.
T cells are named after the organ they develop in, the Thymus.
T cells are divided in different subsets and types depending on the receptors they express on the surface as well as their gene expression and function.
T helper cells, also known as CD4+ T Cells, organize and “help” to alert other cells to coordinate the immune system to clear pathogens (the bad guys). CD4 T cells are divided into various subsets such as T h1, Th2, Th17. Another subset of CD4 T cells includes regulatory T cells also known as suppressor T cells, which are shown in the cartoon above as the police CD4 T cells. Regulatory T cells (T regs) act like suppressor cells that control the immune system and promote tolerance. These cells make sure the immune response doesn’t get out of hand and I therefore think of them as little police officers controlling and ensuring there is order.
Cytotoxic T cells (CTLs), also known as Killer T cells, are a special type of T cells with the ability to kill other cells. Usually they kill cells that have been infected with a virus. This way the virus can no longer use these cells for replicating inside of them. CTLs secrete cytotoxins to kill the other cells and are therefore called “cytotoxic” T cells.
B cells develop in the bone marrow and are therefore called B cells. These cells are responsible for producing antibodies. The antibodies produced by B cells circulate around our body and bind to specific viruses or bacteria to neutralize them and help get them killed by other cells of the immune system.