Size Distribution of Killer Cells During Allograft Response.

The generation of cytotoxic effector cells in the spleen and in the peritoneal cavity of C3H mice immunized with a single injection of H‐2 incompatible P‐815‐X2 mastocytoma cells was studied. At different times after immunization the spleen cells were fractionated according to their size by one‐g velocity sedimentation, and the fractions were tested separately for their cytotoxicity against 51Cr labeled P‐8I5‐X2 cells in vitro. The results indicate that the size of the killer cell changes during the immune response; the early cytotoxic effector cells are large cells (blasts) whereas the late effector cells are small cells (lymphocytes).