Michael Heidelberger was an American immunologist, often regarded as the father of modern immunology. He and Oswald Avery showed that the polysaccharides of pneumococcus are antigens, enabling him to show that antibodies are proteins. He spent most his early career at Columbia University and comparable time in his later years on the faculty of New York University. In 1934 and 1936 he received the Guggenheim Fellowship. In 1967 he received the National Medal of Science, and then he earned the Lasker Award for basic medical research in 1953 and again in 1978. His papers are held at the National Library of Medicine in Bethesda, Maryland.

An antibody (Ab) is the secreted form of a B cell receptor; the term immunoglobulin (Ig) can refer to either the membrane-bound form or the secreted form of the B cell receptor, but they are, broadly speaking, the same protein, and so the terms are often treated as synonymous. Antibodies are large, Y-shaped proteins belonging to the immunoglobulin superfamily which are used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that cause disease. Antibodies can recognize virtually any size antigen with diverse chemical compositions from molecules. Each antibody recognizes one or more specific antigens. Antigen literally means "antibody generator", as it is the presence of an antigen that drives the formation of an antigen-specific antibody. Each tip of the "Y" of an antibody contains a paratope that specifically binds to one particular epitope on an antigen, allowing the two molecules to bind together with precision. Using this mechanism, antibodies can effectively "tag" a microbe or an infected cell for attack by other parts of the immune system, or can neutralize it directly.