THE ANTIGENICITY OF DEGRADED PROTEINS 261 



A single protein molecule may possess more than one set of determinants, in 

 the sense that on injection into an animal two distinct types of specific antibody 

 are produced (Hooker and Boyd 1936). Haurowitz (1937) also was able to demon- 

 strate distinct antibodies to globulin, arsanil-ajZO-globulin and to the arsanilic 

 group alone, in rabbits immunized with an apparently homogeneous preparation 

 of arsanil-azo-globulin. 



Further, Haurowitz, Tunca and Schwerin (1943) have shown that non-antigeni- 

 city may in fact be due to failure of retention on the part of the animal. One 

 hour after injection of arsanil-azo-gelatin, rabbit liver contained 4-4 per cent, of 

 the total dose, as compared with 34 per cent, arsanil-azo-globulin, while the corre- 

 sponding figures in urine were 60 per cent, and 9-2 per cent. Their observation 

 obviously indicates a reconsideration of many examples of non-antigenicity that 

 have been attributed to the absence from the antigenic molecule of substances 

 supposed to render it capable of stimulating antibody-production. A failure of 

 adsorption on to certain cells, or of combination with body substances, may also 

 underlie the varying response of different species of animals to the Type I pneumo- 

 coccal polysaccharide. It is antigenic, or at least capable of stimulating a specific 

 immunity, in man, horse, cat, dog and mouse, but not in the sheep, rabbit, guinea- 

 pig or rat (see Horsfall and Goodner 1936, Downie 1937). 



The Antigenicity of Denatured and Degraded Proteins. — Denaturation by heat or by 

 prolonged exposure to alkali, which lead to racemization, changes the antigenic behaviour 

 of proteins (see Hartley 1931, WeUs 1929, Marrack 1938). Of particular interest is the 

 eflfect of reversible denaturation. When horse or ox serum albumin was denatured by 

 strong urea solution, and regenerated by dialysis, the protein was found to be less antigenic, 

 but apparently had lost none of its specificity (Erickson and Neurath 1943, Martin, Erick- 

 son, Putnam and Neurath 1943). The loss of antigenicity was attributed to breakdown 

 of internal structure of the molecule, the retention of specificity to the preservation of 

 a characteristic arrangement of amino-acid residues in the polypeptide chains. 



These authors also noted an association between antigenicity of various protein prepara- 

 tions and their carbohydrate content. Crystalbumin, which was the most feebly antigenic 

 of the preparations studied, contains no carbohydrate. Lack of carbohydrate cannot 

 be the sole reason for low antigenicity, for the regenerated, feebly antigenic albumins 

 had lost none of their original carbohydrate ; though it is possible that the mode of linkage 

 may have been drastically altered. The carbohydrate in some proteins may be loosely 

 attached, but in others, like serum and egg-white protein, it forms an integral part of 

 the molecule, and is not separable until polypeptide chains are broken. Some influence 

 on antigenicity is to be expected. Indeed, the accumulating evidence that a number 

 of native antigens consist of complexes of polypeptides, lipins and carbohydrates suggests 

 that the antigenicity of a protein may depend on the presence of its non-protein com- 

 ponents. The striking example of the dependence of antigenicity upon a complex of 

 protein and non-protein substances is provided by Morgan and Partridge's (1941) analysis 

 of a bacterial antigen in Shigella shigce. This was separable into a feebly antigenic poly- 

 peptide and a non-antigenic polysaccharide ; recombination of the two restored the full 

 antigenic properties. On the other hand, there is no evidence that the carbohydrates 

 associated with some of the fractions separable from serum albumins and globulins (Coghill 

 and Creighton 1938, Rimington and van den Ende 1940) and from egg albumin and 

 ovomucoid (Ferry and Levy 1934, Sevag and Seastone 1934, Neuberger and Yuill 1940) 

 have any effect on antigenic specificity. The extent to which these carbohydrates are 

 intsgral parts of native protein, however, is not yet clear. 



The immunological reactivity of proteins decreases with progressive hydrolysis. The 

 stage at which the hydrolysed protein ceases to react serologically varies with the protein 



