2IO PETER PERLMANN AND WINFIELD S. MORGAN 



the antigens are both immunologically and chemically different from the 

 serum proteins. All subcellular fractions contain a number of these "liver" 

 antigens in common. These antigens may either be present physiologically 

 or their presence in a certain fraction may be an artefact of fractionation. 

 However, in addition, there also exists a considerable number of antigens 

 typical of various fractions. Thus, the microsomal fraction of rat liver is 

 characterized primarily by five to six strongly antigenic proteins which 

 can be extracted with sodium deoxycholate, non-ionic detergents such as 

 lubrol W (cetyl alcohol polyoxyethylene condensate) [ii, 5], or with 

 phospholipase A [i, 20]. These antigens seem to be lipoproteins. They 

 are difficult to characterize electrophoretically. However, it has been 

 possible to isolate two of these antigens in an immunologically pure form. 

 A lubrol extract of microsomes w'as separated by chromatography on 

 DEAE cellulose [23], using constant pH (o'035 m tris-buffer, pH 7*8) 

 and a gradient of KCl for elution. The presence of 0-2% lubrol in all 

 reagents was necessary for fractionation (unpublished results). 



The microsomal subfraction which remains insoluble after treatment 

 of the microsomes with detergent (ribonucleoprotein particles) contains 

 some additional weak antigens. These antigens can be visualized in the 

 diffusion plates after extraction with chelating agents at pH 7-4 [i, 20]. 

 Their chemistry is so far unknown. 



The microsomal antigens described above are different from the anti- 

 gens typical of liver cell sap. Moreover, when extracts of the liver fractions 

 are compared with microsomal extracts or cell sap from other rat organs, 

 additional differences are found. This is illustrated in Fig. i. This shows 

 the reactions obtained when lubrol extracts of microsomes from liver, 

 kidney, pancreas, testis, spleen and brain were reacted with the correspon- 

 ding anti-microsomal sera. Each line in these photographs represents the 

 precipitate formed by one, or sometimes several antigens, with their 

 corresponding antibodies. Fusion of precipitates from neighbouring 

 containers suggests an immunological identity of the antigens, while the 

 precipitates of unrelated antigens cross. The formation of spurs in certain 

 cases indicates either cross reactions or an immunological heterogeneity of 

 the precipitates [12]. 



None of the antigens appearing in Fig. i is due to serum proteins, 

 since antibodies against these had been removed in advance by means of 

 absorption of the antisera with rat serum. Roughly, Fig. i demonstrates 

 that the microsomal extracts of liver, kidney, and pancreas are highly 

 organ-specific in the sense that they give the greatest number of precipitates 

 with their homologous antisera. The anti-liver microsomal serum contains 

 the largest number of antibodies reacting with antigens present in extracts 

 from other organs. In contrast, lubrol extracts of microsomes from testis 

 contain only a few components ; in common with liver microsomes spleen 



