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.
B cells (aka B lymphocytes) are one of many types of cells in the immune system. There are many millions of them spread throughout the body. They are the only cells in the body that produce factors called antibodies (aka immunoglobulins) that do many important things. People with too few B cells or the antibodies they produce can have trouble defending against common microbes (viruses, bacteria, etc) and may get very serious and life-threatening infections.
Antibodies can bind to proteins and other biomolecules that are floating around in the body or that are attached to other cells. When each B cell develops, it makes a series of changes to its genetic code that end up producing an antibody with a random binding specificity. This makes every new B cell likely to recognize something different than every other B cell in the body.
That's important because it leads to the total population of B cells being able to recognize almost any kind of protein or biomolecule in the world, including those that are on dangerous microbes that the person has never been exposed to before. When a B cell finds something that it recognizes through its surface antibody (aka B cell receptor) it can start to become activated.
If B cells get activated, they can divide to form daughter cells with the same specificity leading to increased number of them. They can also make other genetic changes that allow their antibodies to leave the cell and spread throughout the rest of the body. This is the basis of how most vaccines work. By activating B cells that are specific toward the proteins on the particular microbe or factor (flu virus, measles virus, tetanus toxin, etc) that is being targeted by the vaccine, the immune system gets more prepared to recognize and eliminate those microbes and factors.
Many of you may wonder how the immune system is supposed to work or why it sometimes doesn't do what it is supposed to do. In this space, we hope to be able to answer questions you may have in a clear and concise way. Please ask us using the comments box, and we will do our best to respond to you and others who may have similar questions. From time to time, we will also post general topics for those of you who would like to follow along.