524 Heredity in Protozoa 



Antigenic types and cytoplasmic inheritance 



Hereditary antigenic variations in Paramecium aurelia have been 

 reported by several workers. According to Harrison and Fowler (20), 

 such variations may arise spontaneously. The stability of the variant 

 differs with the strain and has ranged from less than three months to 

 about four years. Similar variations have been induced in P. aurelia 

 (stock 51) by exposure to X-rays (82) and to homologous antisera (82, 

 89). Temporary changes, lost after 1-15 fissions, also have been induced 

 by exposure to trypsin and by maintenance of cultures at 14° for a 

 number of generations (39). Antigenic types may be modified in different 

 ways by different experimental methods. Types B, C, and D may be con- 

 verted into A by incubation at 32°, and types A, C, and D may be 

 changed to B by incubation at 12°. All the various types remain stable 

 at 27° if the food supply is controlled to maintain one fission a day (85). 

 The antigenic type in variety 4 of P. aurelia is said to depend upon 

 competition between plasmagenes (85, 89). 



In the only experiments with bacteria-free cultures, an antigenic modi- 

 fication, exhibited as insensitivity to antiserum, has been produced by 

 exposure of Tetrahymena to homologous antiserum, but the ciliates 

 reverted to the original type after two transfers in normal culture 

 medium (69). 



The status of antigenic varieties in P. aurelia is not yet settled. Since 

 there is no evidence for micronuclear control, it has been suggested that 

 cytoplasmic inheritance determines the observed behavior in conjugation 

 and autogamy (82, 86). Results obtained in conjugation of types A and 

 B (Fig. 9. 4) are attributed to a lack of cytoplasmic transfer in some cases, 

 and to the transfer of large or small amounts of cytoplasm in others. 

 After an A X B cross, the inbreeding of type A exconjugant lines yields 

 only type A; that of type B exconjugants, only type B. Cytoplasmic 

 inheritance is believed to offer the most logical explanation for these 

 various results. 



Possible mechanisms involved in the antigenic transformations of 

 P. aurelia have been discussed by several workers (3, 22, 89), and Beale 

 has suggested that the potsulated plasmagenes are the antigens them- 

 selves (3). 



LITERATURE CITED 



1. Ackert, J. E. 1916. Genetics 1: 387. 



2. Austin, M. L. 1948. Physiol. Zool. 21: 69. 



3. Beale, G. H. 1948. Proc. Nat. Ac. Sci. 34: 418. 



4. Bishop, A. and B. Birkett 1948. Parasitol. 39: 125. 



5. Caldwell, L. 1933. /. Exp. Zool. 66: 371. 



6. Chen, T.-T. 1940. /. Hered. 31: 249. 



7. Cohen, B. M. 1934. Genetics 19: 25. 



8. 1934. Genetics 19: 40. 



