Control of the immune response. I. Depression of DNA synthesis by immune lymph node cells.

The DNA response in the regional lymph nodes draining the site of immunization with contact sensitizing agents was assessed by measuring the uptake of radioactive iododeoxyuridine. The DNA response in the regional lymph nodes reached a peak on day 3 after immunization and fell to pre-immunization levels by day 6. The hypothesis was tested that lymph node cells from mice immunized with picryl chloride might depress the DNA response to the same antigen. Immune lymph node cells were injected intravenously and the recipient mice were immunized with picryl chloride on the same day. The immune cells depressed the DNA response on day 4 by an average of about 60 per cent. Smaller but significant depression also occurred on day 3. The cells responsible for the depression appeared in the regional lymph nodes 3-4 days after immunization and disappeared by day 21. The transfer of small numbers of immune cells (less than 2-5 X 10(6)) increased the DNA response in recipients 4 days after immunization with picryl chloride. The depression of the DNA response was largely specific. Pooled data from ten experiments showed that cells immunized with 4-ethoxymethylene-phenyl oxazolone ('oxazolone') caused no depression of the DNA response to picryl chloride, although in two of these experiments significant depression of about 21 per cent was seen. Similar results were obtained when immune cells were injected into mice immunized with 'oxazolone'.