The natural immune system fights off foreign pathogens, such as bacteria and viruses. Specific immune cells, called B-lymphocytes or B-cells, identify proteins called antigens on the surface of invading cells.
When a B cell detects an antigen, it causes the production of proteins, called antibodies, that bind to antigens.
When B cells produce an antibody, they can continue making the antibody if the same antigen appears in the future. It is called adaptive immunity.
Immunity offers protection that extends beyond the personal level. For example, when individuals have developed an adequate antibody response, benefits such as “herd immunity” become possible.
Herd immunity occurs when a percentage of a population develops immunity to an infectious disease.