How are T Cells Activated (Simplified)

What Are T Cells

T cells are a type of white blood cell (lymphocytes) that play a central part in regulating our immune system. T cells differ from other types of lymphocytes, such as B cells and natural killer cells, by having a T-cell receptor on the cell surface. These cells are named T cells because they mature in the thymus from blood precursor cells called thymocytes. 

How T Cells Help Remove Harmful Cells

On the surface of the other immune cells types, phagocytes and B cells, there are receptors that bind to proteins found on harmful cells, such as bacteria, viral infected cells or mutated cells like cancer. (Both phagocytes and B cells have very different mechanisms of action but have a similar outcome involving T cells.) The harmful cells are then engulfed and denatured. A small part of the harmful cell is then bound to a protein complex called the major histocompatibility complex II (MHCII) and transported to the surface of the phagocyte or B cell. Having the MHCII on the surface of the cell allows the Helper T (Th) cells to find it and bind to it. The Th cell, now bound to the MHCII complex, activates the Th cell. When active, the Th cell, believing that the body is being invaded, multiplies many times and secretes small molecules called cytokines. The cytokines are chemical alarm bells that can notify more immune cells that there are harmful cells within the body. Th cells also activates B cells by binding to it, leading to an overall increase in B cells, and Th cells while also activating cytotoxic T cells (Tc) cells from the release of cytokines. Overall, this mechanism works to protect the body from disease by finding harmful cells and removing them. 

Scientists can now engineer T cells to attack cancer cells in the body. So far, there has been success in treating blood and lymph cancers but it is still difficult to treat solid tumors, especially in difficult to reach parts of the body. Some questions that need to be answers revolved around how to artificially modulate the activity of the T cells, and how would a better understanding behind the mechanical forces of the T cells give insight on treatment of solid tumors. The next few articles will be answering these questions while showing how Dr. Butte's lab is playing an important role in this process.