DNA synthesis in vitro by cells from mice immunized with picryl chloride: effect of injection of immune cells.

Mice were immunized with picryl chloride and the regional nodes taken at various times afterwards. These cells spontanesouly synthesized DNA in vitro as measured by thymidine incorporation over an 18-hour period and the peak incorporation occurred when the cells were takin on day 3. When the mice were injected with cells taken 5 days after immunization with picryl chloride and then immunized, there was a depression of the spontaneous DNA synthesis in vitro. This was absent on day 2, most marked on day 3 and still present on day 4. Cells from donors immunized with 4-ethoxymethylene-2-phenyloxazolone had a smaller but definite effect. Attempts to reproduce the phenomenon by in vitro mixtures of cells taken at various times after immunization in vivo were unsuccessful.