Heidelberger and the demystification of antibodies

Heidelberger and Avery’s early experiments hinged on a simple element: nitrogen. Based on its presence or absence, the duo showed that the antibody-reactive substances on pneumococcal bacterial capsules were nitrogen-free carbohydrates, and that the reacting antibodies were nitrogencontaining proteins (see “How Heidelberger and Avery sweetened immunology” JEM 202:1306). The discovery that antibodies are proteins was a notable achievement, particularly at a time when the nature of antibodies—substances known only to reside in proteinaceous serum— remained a mystery. But many contemporary immunologists consider the quantitation of the precipitin reaction an equally important accomplishment.