CHAPTER XVIII 

 MODIFIED AND CONJUGATED ANTIGENS* 



Early Work on Modified Antigens. — The first work on modified 

 antigens was that of Obermayer and Pick (1906). They made the 

 important observation that chemical alteration of proteins leads to 

 the appearance of new serological properties. They introduced 

 iodine and NO 2 into proteins and thus formed iodoproteins and 

 xanthoproteins, respectively. Antibodies produced by injecting 

 these altered proteins gave visible (precipitin) reactions with any 

 protein similarly altered but not with the original unaltered 

 protein. It was the general belief at that time that the capacity 

 of inciting antibody production as well as of reacting in vitro 

 with antibodies was the property solely of ])roteins. This notion was 

 retained long after the publication of Obermayer 's and Pick's 

 papers and the idea that antibodies could react with simple chem- 

 ical substances was not considered at all. It is now known that 

 antibodies for xanthoprotein or iodoprotein will not react Avith 

 NOo or lo (or KI), respectively, but are specific for chemically 

 modified portions of the proteins. This should be kept in mind be- 

 cause it really differentiates the discoveries of Landsteiner from 

 those of Obermayer and Pick. 



Early Work on Conjugated Antigens. — Landsteiner began by 

 confirming Pick's work and extending it to include acetylated and 

 methylated proteins. He then started a new line of investigation, 

 namely, an attempt to manufacture antigens by combining simple 

 substances with proteins. From this work, he says, two unfore- 

 seen facts emerged. 



First, that it is possible to produce antibodies which are specific 

 for substances of known constitution. These results were pub- 

 lished more than ten years after the studies of Obermayer and 

 Pick. The second unforeseen result (1920) was that by means of 

 a new method, namely, the "inhibition reaction" antibodies were 



*r>r. R. Q. Brewster of the Organic Chemi.stry Department collaborated with 

 the author in the preparation of part of this chapter. 



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