Antigenic variation during cellular aging in Paramecium tetraurelia

Clones of Paramecium tetraurelia undergoing cellular aging were exposed to two antisera, anti-32 and anti-25, raised against surface antigen isolated from cells grown at 32 degrees C or 25 degrees C. When young clones were exposed to the two antisera about 50% were immobilized by anti-32 while others were not immobilized by either antisera. These clones were grouped as group A or B depending upon their sensitivity or nonsensitivity to the two antisera. Young cells of group A were immobilized by anti-32 and during aging these cells either maintained the same antigenic type or transformed to another. Young group B clones were not immobilized by either antisera but gradually became sensitive to anti-32. Some clones from both groups showed sensitivity to both antisera. The possible mechanism of antigenic variation during fission age is discussed.