282 THE ANTIGENIC STRUCTURE OF BACTERIA 



undergone several successive precipitations by the same reagent, or successive 

 crystallizations from the same solvent, is no guarantee of its purity, for loosely 

 bound heterogeneous complexes will exhibit constant precipitability, and mixed 

 and contaminated crystals are common in biochemistry. For further details 

 on this important point, reference should be made to Pirie's (1940) review of 

 the subject. 



The Sharing of Antigenic Components between Unrelated Bacteria, or between 

 Bacteria and Other Cells. 



In the course of the numerous studies that have been made on antigenic structure, 

 instances have come to light of the sharing of a particular antigenic component by 

 bacteria that show no systematic relation to one another, or by bacteria on the 

 one hand and plant and animal tissues on the other. It is possible in some cases 

 that the reported immunological cross-reactions may have been due to the presence 

 of contaminating antigens discussed in the previous section. It will be noted 

 that the various types of pneumococci figure largely in the examples given below. 

 This predominance is not necessarily a peculiarity of the species ; more probably 

 it is a reflection of the extensive American work on the pneumococcal antigens. 



Thus, pneumococcus Type I and certain coliform bacilli are serologically related (Barnes 

 and Wight 1935). The capsular polysaccharide of pneumococcus Type II is closely 

 similar to that of the Type B pneumobaciUus (Avery et al. 1925, JuUanelle 1926) ; to 

 polysaccharides isolated from a species of yeast (Sugg, Richardson and NeiU 1929) and to 

 a species of Leuconostoc (Sugg and Hehre 1942) ; and cross-reactions occiu- between this 

 type and Past, lepiseptica (Dingle 1934). 



Antisera to Types II and III pneumococci react with a polysaccharide obtained by 

 partial hydrolysis of gum arabic (Heidelberger, Avery and Goebel 1929), and of gum 

 acacia, cherry and other vegetable gums (Marrack and Carpenter 1938). Miller and 

 Boor (1934) report cross -reactions between Type III pneumococcus on the one hand, and 

 meningococcus and gonococcus on the other, and KauflFmann and Langvad-Nielsen (see 

 Morch 1942) between Type XXXV and a Salmonella species. There are similar relation- 

 ships between Type VI pneumococcus and H. influenzce Type a (Chapman and Osborne 



1942, Neter 1943, Zepp and Hodes 1943). 



The polysaccharide of pneumococcus Type XIV is related to that which characterizes 

 the antigen of the human Group A red blood cell (Goebel et al. 1939), and both are related 

 to the somatic polysaccharide of the anthrax bacillus (Ivanovics 1940). 



Many other examples could be cited of relationship between markedly differing species, 

 particularly within the group of the Gram-negative intestinal baciUi. Perhaps one of the 

 most striking antigenic relationships is that between certain species of Proteus vulgaris 

 and certain species of Rickettsia (see Chapter 39), where the antigenic varieties in one 

 group are to some extent paralleled by antigenic varieties in the other. 



An equally curious example of this sharing of antigenic components is afforded by the 

 presence in a wide variety of bacteria of Forssman's heterophile antigen (see p. 1089), 

 which is a constituent of the red blood corpuscles and tissue cells of certain animal species 

 (see Rothacker 1913, lijima 1923, Schmidt 1925, Meyer 1926, 1930, 1931, Meyer and Morgan 

 1935, Powell 1926, Yasui 1929, Combiesco et al. 1930, Eisler 1931a, h, Eisler and Howard 

 1931, 1932, Bailey and Shorb 1931, Buchbinder 1935, Morgan 1937, Goebel and Adams 



1943, Goebel et al. 1943). 



There is, of course, nothing very bizarre in the occurrence of identical, or closely 

 similar, antigenic groupings in living cells that have no close systematic relationship. 

 The specificity that antigen-antibody reactions detect is, as we have seen, a chemical 

 one. The fact that it is also biological, in the systematic sense, depends on the 



