Particularly important was the work of Paul Ehrlich ( 1854-1915 ) , who proposed the side-chain theory to explain the specificity of the antigen-antibody reaction ; his contributions to the understanding of humoral immunity were recognized by the award of a Nobel Prize in 1908 , which was jointly awarded to the founder of cellular immunology , Ilya Mechnikov ( 1845-1916 ) . Particularly important was the work of Paul Ehrlich , who proposed the side-chain theory to explain the specificity of the antigen-antibody reaction ; his contributions to the understanding of humoral immunity were recognized by the award of a Nobel Prize in 1908 , which was jointly awarded to the founder of cellular immunology , Elie Metchnikoff .