212 PETER PERLMANN AND WINFIELD S. MORGAN 



and brain microsomes seem to be more or less devoid of lubrol-extractable 

 antigens specific for these organs. 



A somewhat different picture emerges when the cell saps from these or- 

 gans are compared in similar experiments. In this case, the number of com- 

 mon antigens in the different organs is greater. In general, it may be stated 

 that the "organ specificity" of the cell sap is less than that of the micro- 

 somes, although organ specific antigens are present in these fractions also, 



A full description of these results will be given elsewhere [19]. Ob- 

 viously, no immediate conclusions can be drawn from experiments such as 

 these, since the various homogenates are histologically heterogenous, the 

 cytology of some of the microsomal preparations is badly known, and the 

 chemistry of the antigens has not yet been studied. However, it appears 

 that further studies along these lines should render important information 

 regarding the chemistry and genetics of microsomal structures in different 

 types of cells. 



The presence of transitory antigens in microsomal fractions 



While the aim of the above-mentioned studies is to investigate the 

 chemical composition and relationship of subcellular structures, the 

 immunology of the microsomes has another important aspect. Microsomes 

 are believed to be important sites of protein synthesis. While the synthesis 

 of protein is assumed to take place in or on the ribonucleoprotein particles, 

 the endoplasmic membranes of the microsomal fractions are often believed 

 to possess a regulatory function and to be involved in transportation of 

 freshly formed protein out of the cells. (See [25] for references and dis- 

 cussion.) During recent years, there has accumulated evidence indicating 

 that microsomes can be characterized immunologically by the antigens 

 which are believed to be the transitory products of their synthetic or 

 transporting activities. Thus, in a number of animal species, serum albumin 

 can be extracted from the microsomes of the liver, where it is synthesized 

 [4, 21, 22]. Similarly, antibody-active proteins have been extracted from 

 microsomes of lymph nodes or spleen of immunized animals [2, 6]. It has 

 also been reported that ribosomes from Escherichia coli can be precipitated 

 specifically by means of an antiserum against beta galactosidase [8]. 



Certain results obtained in our laboratory also point in that direction. 

 Thus, injection of rat liver microsomes into rabbits leads to a strong pro- 

 duction of antibodies, not only against the "liver" antigens shown above, 

 but also against a great number of serum proteins of the rat [i, 20]. Antisera 

 against microsomes of spleen contained antibodies against rat gamma 

 globulin, in very high concentration. In contrast, the antisera against 

 microsomal fractions of the other organs shown in Fig. i contained none, 

 or only trace amounts, of such antibodies [19]. 



