558 



Ontogeny of Immunological Properties 



cannot by itself induce antibody formation 

 or precipitate antibodies produced against the 

 conjugated protein.* However, it can combine 

 with the antibodies to form soluble com- 

 plexes and thereby inhibit the antibodies 

 from precipitating with the conjugated pro- 

 tein. While the specificity of these reactions 

 is so great that stereo-isomers can be dis- 

 tinguished, cross-reactions are also obtained 

 with various haptens. Extensive studies of 

 these have shown that the extent of cross- 

 reaction is dependent upon the degree of 

 similarity in size, shape and constitution of 

 the "working end" of the hapten. 



When an azoprotein is used for immvmiza- 

 tion the antiserum generally contains anti- 

 bodies directed against the uncoupled protein 

 as well as those against the hapten. It is 



Antigen 



may depend upon relatively small determi- 

 nant groups rather than on the whole struc- 

 ture of the molecule, and that the molecule 

 may contain more than one kind of determi- 

 nant group. Unfortvmately very little is 

 known about the size, number and kind of 

 determinant groups of natural proteins. Ex- 

 periments by Landsteiner ('42) with hydrol- 

 ysates of silk protein have shown that pep- 

 tides of molecular weight of 600 to 1000 can 

 specifically inhibit the precipitation of the 

 intact protein by its antiserum. For the pres- 

 ent we can only conclude by analogy with 

 the results of experiments on the coupled 

 proteins that natural proteins may induce 

 the formation of more than one kind of anti- 

 body. Some of the antibody molecviles wovdd 

 be specific for one determinant group, some 



Fig. 207. Diagram illustrating the three kinds of antibody molecules that may be produced in response to 

 immunization with an antigen containing two different kinds of determinant groups. 



clear, then, that a single kind of protein can 

 give rise to more than one kind of antibody. 

 This is illustrated further when two different 

 haptens (A and B, see Fig. 207) are coupled 

 with a protein. Thus Haurowitz and 

 Schwerin ('43) obtained distinct anti-A and 

 anti-B antibodies upon injection of such an 

 antigen. They did not find a third possible 

 type, anti-AB. However, Dodd ('52) presents 

 strong evidence for this type of antibody in 

 grovip O humans immunized with mixed A 

 and B antigens, as well as for its occurrence 

 in normal human group sera (see also 

 Bird, '53). A less satisfactory interpretation 

 is that some anti-A and anti-B antibodies in 

 group O sera are more cross-reacting than 

 are others. 



The work with haptens serves to emphasize 

 that in natural proteins antigenic specificity 



* A complex hapten, formed by coupling more 

 than one molecule with a simple substance such as 

 resorcinol, can form a precipitate with the anti- 

 bodies produced by injection of the azo-protein (see 

 Landsteiner and van der Scheer, '32, '33; Pauling 

 et ah, '41). 



for another, and some for combinations of 

 determinant groups. If two different proteins 

 possess a common determinant group, then 

 the antiserum induced by one of the proteins 

 will cross-react with the other. 



When antisera for two natural proteins of 

 diverse origin cross-react there are, then, at 

 least three possible interpretations. One is 

 that, of the various kinds of determinants 

 of the two proteins, one or more may be 

 identical. Another is that various regions of 

 the two proteins may possess some degree 

 of structural similarity. The third is the pos- 

 sible presence of one of the proteins as a 

 chemically undetected contaminant in prep- 

 arations of the other. This uncertainty as to 

 interpretation must be taken into account in 

 attempting to analyze investigations on the 

 antigens of adult and embryonic tissues, 

 since cross-reactions are very commonly ob- 

 tained with such material. In other words, 

 it is important to know what is being detected 

 by the antiserum that is employed. To some 

 extent the difficulties are overcome by the 

 use of the methods of absorption whereby 



