7IO ANTIGENS AND THEIR SPECIFICITY 



These and numerous other observations indicate that the chief factor in deter- 

 mining immunological specificity, at least in immunizing with pure proteins, is the 

 chemical composition of the antigenic protein. In the case of complex antigens the 

 specificity may depend on the composition of the protein molecule itself, but in some 

 cases, e.g., the Forssman heterogenetic antigen, on lipoid radicals attached to the 

 antigenic protein. In the case of some bacteria carbohydrate complexes attached to 

 the protein molecule seem to be important determiners of specificity.' Thus, with 

 the pneumococcus the bacterial protein seems to determine species specificity, while 

 the group specificity is determined by the carbohydrates of the capsule. 



Whether carbohydrate protein complexes also are concerned in the specificity of 

 animal antigens has not yet been determined. Lipoid-protein complexes probably are 

 often important in determining the specificity of animal antigens; for example, the 

 two globulin fractions of serum, euglobulin and pseudoglobulin, are immunologically 

 distinguishable, but seem to differ from each other chemically solely in that the 

 euglobulin has a lipoid radical. The work of Landsteiner indicates that animal cells 

 when used as antigens, as in the production of hemolysin by immunizing with red 

 corpuscles, owe their specificity to complexes of proteins and non-protein radicals, 

 probably lipoidal.^ 



Also, there is reason to believe that the Wassermann reaction may depend on an 

 autoimmunization to lipoid-protein complexes set free by tissue or spirochete dis- 

 integration in syphilis.^ Apparently, then, when the antigen is a pure protein, speci- 

 ficity is determined by the structure of the protein itself; but when cellular antigens 

 are concerned, specificity depends more on complexes of protein and non-protein 

 radicals. 4 



' Cf. Pryde, J.: loc. ciL; also chap, lii in this volume. ■ 



' See Landsteiner, K., and van der Scheer, J.: /. Exper. Mei., 41, 427. 1925; 42, 123. 1926. 



3 See Weil, A. J.: Zlschr. f. Immunitdtsforsch. u. exper. Therap., 46, 81. 1926; Sachs, H., and 

 Klopstock, A.: Deitsche mei. Wchnschr., 53,394- 1927. 



4 For a discussion of complex antigens see Landsteiner, K.: Klin. Wchnschr., 6, 103. 1927. 



