IMMUNITY: AN ACCESSIBLE PATH TO EVOLUTION

Immune responses elicited by routine vaccines that every student receives illustrate the principles of evolution. The white blood cells, known as B lymphocytes, are the cells possessing the capacity to make antibodies. Antibodies are serum proteins that mediate immunity to bacteria, viruses, and other pathogens by recognizing and binding to molecular components, called antigens, produced by those pathogens. Each B lymphocyte produces antibodies that all possess the identical antigen-binding structures. The antigens in a vaccine confer a reproductive advantage on those B lymphocytes with antibody receptors able to interact with one of those antigens. Thus, the immune response represents a Darwinian process, referred to as clonal selection.