Gerald Edelman, at Rockefeller University, and Rodney Porter, at the University of Oxford, independently determine in the late 1950s and through the 1960s the complete molecular structure of antibodies (immunoglobulins), the proteins the immune system produces to recognize and neutralize specific pathogens. Porter demonstrates, through controlled enzymatic digestion, that the antibody molecule can be fragmented into functionally distinct pieces: a region that binds specifically to the pathogen, and a separate, constant region responsible for activating other parts of the immune system. Edelman determines that each antibody molecule is composed of four protein chains — two "heavy" chains and two "light" chains — joined together, with a characteristic Y shape, and completes the full amino acid sequence of a complete human immunoglobulin, a considerable technical achievement given the molecule's size. The combination of both works reveals the structural mechanism that allows the immune system to generate an almost unlimited variety of distinct antibodies — capable of recognizing virtually any possible pathogen — from a common molecular architecture with variable and constant regions, a principle that would become the foundation of molecular immunology and, decades later, of therapies based on monoclonal antibodies.