B cell

B cells are important parts of your immune system. They are a type of lymphocyte, which is a kind of white blood cell.

These cells help protect you through humoral immunity. This means they use special molecules called antibodies to fight germs. B cells can either send these antibodies out into your body or keep them on their surface. When they are on the surface, they are called B-cell receptors, or BCRs. These receptors are very specific to one target. They allow the cell to find and bind to a foreign antigen. An antigen is a tiny part of a germ that the cell recognizes.

Making a B cell is a step-by-step process. It starts with hematopoietic stem cells in the bone marrow. These cells change into different types of cells through several stages.

First, they become multipotent progenitor cells. Then, they turn into common lymphoid progenitor cells. As they develop, the cells undergo a process called V(D)J recombination to build their receptors. The cells must pass two tests called selection. In positive selection, the cell must receive the right signals to grow. In negative selection, the cell must not attack your own body. If a B cell tries to bind to your own body's parts, it is removed. This helps the body reach a state of central tolerance.

Scientists have learned a lot about where these cells grow. In mammals, B cells mature in the bone marrow. This is the soft center of your bones. In birds, they grow in a special organ called the bursa of Fabricius.

This organ was first found by researchers Timothy Chang and Bruce Glick. Because of this discovery, the "B" in B cell actually stands for bursa. Many people think it stands for bone marrow, but that is not the case for birds. This shows how much we can learn from studying different animals.

Once B cells are mature, they move to places like the spleen or lymph nodes.

Here, they wait for an antigen to arrive. There are two main ways a B cell wakes up. Some antigens are T cell-dependent. These are usually foreign proteins that need help from T cells to work. This process takes a few days, but the antibodies are very strong. Other antigens are T cell-independent, like certain sugars or DNA. These allow the B cell to react much faster.

This fast reaction helps your body respond to a threat quickly.

After a B cell is activated, it changes into a new kind of cell. It might become a plasmablast, which is a short-lived cell. Plasmablasts make early, weaker antibodies to help right away.

Other B cells become long-lived plasma cells. These cells live a long time and make many strong antibodies. They often move back to the bone marrow to stay. Some B cells become memory B cells instead. These cells remember the specific germ. If that germ ever enters your body again, the memory cells can jump into action. This keeps you safe from getting sick from the same germ twice.