Biological Systems MCAT Practice Exam

What happens to B cells that attack normal cells?

1. They undergo apoptosis

2. They become activated

3. They form memory cells

4. They differentiate into plasma cells

The correct answer is: They undergo apoptosis

B cells that attack normal cells undergo a process known as apoptosis, which is a form of programmed cell death. This is a crucial mechanism in the immune system designed to maintain self-tolerance and prevent autoimmunity. When B cells recognize and bind to self-antigens, which are components of normal cells, their activity is typically suppressed or leads to their elimination. This ensures that the immune system does not mistakenly attack the body’s own tissues, preventing conditions such as autoimmune diseases. This process is part of central tolerance during B cell development in the bone marrow, where B cells that strongly recognize self-antigens are usually eliminated. If they escape this process and still attack normal cells, mechanisms such as anergy (functional inactivation) or apoptosis occur to prevent harmful actions against the body's own healthy cells. In contrast, the other options describe processes that typically occur under specific circumstances. Activation typically refers to the process that B cells undergo when encountering a foreign antigen, which is not the case for those attacking normal cells. Memory cells are formed after a successful immune response to a pathogen, allowing for quicker responses to future infections, and plasma cells are differentiated forms of B cells that actively produce antibodies against antigens. Both of these processes are not associated with B cells that