A 'killer' B cell is so named because it has the ability to induce the death of another cell. In particular, these B cells are very good at killing another type of immune cell, the T helper cell, which is important because T helper cells are responsible for driving many types of autoimmune and allergic diseases. The way the B cell does this is by expressing a protein called Fas ligand that can bind to its partner Fas on the surface of a target cell. This binding, accompanied by other signals, sets off a cascade of events in the targeted cell that leads to changes in its internal structure and ultimately to the target cell imploding through a process called programmed cell death or apoptosis. One of the interesting things that we have found out is that the killer B cells not only can express Fas ligand on their cell surface, but they also make tiny vesicles that contain Fas ligand that have the potential to travel throughout the body looking for T helper cells to target. This is important because killer B cells are normally located in the lining of the intestines and in the lungs, where they are not likely to encounter their prey. Their location and other interesting aspects of their biology make it quite likely that killer B cells play an important role in reducing severe allergic reactions such as asthma and food allergy. There is also evidence that they are involved in tolerance toward self antigens and the suppression of autoimmune diseases such as rheumatoid arthritis and type 1 diabetes. We are working very hard to understand as much as possible about these unique cells, and in developing ways to use them as therapy for many types of diseases.