B cells, which are a type of white blood cell. When a foreign substance, known as an antigen, enters the body, B cells are activated to produce antibodies specific to that antigen. Antibodies bind to antigens and mark them for destruction by other immune cells, such as macrophages and natural killer cells. This process is known as the humoral immune response. Antibodies also play a role in immune memory, allowing the body to respond more quickly and effectively to future infections by the same pathogen.
