Editing Side-chain theory (section)

==Concept==
[[File:Diagrams illustrating the side-chain theory of Paul Ehrlich Wellcome M0013303.jpg|frameless|right]]
[[File:Diagrams illustrating the side-chain theory of Paul Ehrlich Wellcome M0013304.jpg|frameless|right]]
Ehrlich supposed that living cells have [[side chain]]s in the same way [[dyes]] have side chains which are related to their coloring properties. These side chains can link with a particular toxin (or any antigen), just as Emil Fischer said [[enzymes]] must bind to their [[receptor (biochemistry)|receptor]]s "as lock and key."<ref>{{cite book|last1=Kindt|first1=Thomas J.|last2=Capra|first2=J. Donald|title=The Antibody Enigma|date=1984|publisher=Springer US|location=Boston, MA|isbn=978-1-46844676-0|page=6|url=https://books.google.com/books?id=VBcGCAAAQBAJ}}</ref>

Ehrlich theorised that a cell under threat grew additional side chains to bind the toxin, and that these additional side chains broke off to become the [[antibody|antibodies]] that are circulated through the body. According to this theory, the surface of white blood cells is covered with many side chains that form chemical links with the antigens. For any given antigen, at least one of these side chains would bind, stimulating the cell to produce more of the same type, which would then be liberated into the blood stream as antibodies. According to Ehrlich, an antibody could be considered an irregularly shaped, microscopic, three-dimensional label that would bind to a specific antigen but not to the other cells of the organism. It was these antibodies that Ehrlich first described as "[[Magic bullet (medical)|magic bullets]]", agents that specifically target toxins or pathogens without harming the body.<ref>{{cite journal|last1=Tan|first1=SY|last2=Grimes|first2=S|title=Paul Ehrlich (1854-1915): man with the magic bullet|journal=Singapore Medical Journal|year=2010|volume=51|issue=11|pages=842–843|pmid=21140107|url=http://smj.sma.org.sg/5111/5111ms1.pdf}}</ref><ref>{{cite journal|last1=Chuaire|first1=Lilian|last2=Cediel|first2=Juan Fernando|title=Paul Ehrlich: From magic bullets to chemotherapy|journal=Colombia Médica|year=2009|volume=39|issue=3|page=online|url=http://colombiamedica.univalle.edu.co/index.php/comedica/article/view/597/902#4}}</ref>

Ehrlich suggested that interaction between an infectious agent and a cell-bound receptor would induce the cell to produce and release more receptors with the same specificity. According to Ehrlich’s theory, the specificity of the receptor was determined before its exposure to antigen, and the antigen selected the appropriate receptor. Ultimately all aspects of Ehrlich's theory would be proven correct with the minor exception that the "receptor" exists as both a soluble antibody molecule and as a cell-bound receptor; it is the soluble form that is secreted rather than the bound form released.