fuckyeahmolecularbiology:

Another picture of T cells - the soldiers of the immune system. They destroy rogue cells and intruders, and are made in a two-step process that starts in the bone marrow and finishes in a small gland above the heart – the thymus. In the thymus, they mature into battle-ready cells with specialised skills.

It was once thought that T cells (here dyed red) matured by a complicated sequence of chemical signals; however, recent findings demonstrate that only four proteins are required. Researchers discovered this by manipulating the chemical environment of a mouse embryo thymus (dyed blue and green), flicking genes on and off like light switches. The discovery prompts a paradigm shift, which could boost research into new drugs. Novel treatments could help rekindle immunity after cancer therapy, and even lead to the creation of artificial thymus glands.