Edited by
Charlotte Slayton Kaetzel

2007

Although the existence of a humoral “immune” system has been appreciated for millennia, it was not until 1890 that “antibodies” were identified as serum proteins capable of recognizing and neutralizing antigens with a high degree of specificity (von Behring and Kitasato, 1890). Nearly 50 years later, the advent of physicochemical techniques for analyzing the size and charge of serum proteins led to the proposal that antibodies comprised multiple isotypes (Tiselius and Kabat, 1939).