Contact sensitivity in the mouse. XII. The use of DNA synthesis in vivo to determine the anatomical location of immunological unresponsiveness to picryl chloride.

[I]iododeoxyuridine was used to assess the DNA synthesis in the lymph nodes and spleen of mice exposed to picrylating agents. Skin painting with picryl chloride causes both contact (delayed) hypersensitivity and antibody production. It also increases DNA synthesis in the draining lymph nodes and spleen. The lymph node response peaks at day 3 and reverts to normal by day 7. In contrast, the DNA synthesis in the spleen shows three well-defined peaks on days 2, 5 and 8. The total DNA synthesis in the first 4 days is 0.6–2.4 times greater in the spleen than in the draining lymph nodes. It is known that the intravenous injection of picryl sulphonic acid abolishes the contact sensitivity which otherwise follows skin painting with picryl chloride but has less effect on antibody production. This pretreatment depresses and may virtually abolish the DNA synthesis response of the lymph nodes to skin painting with picryl chloride. In contrast the response in the spleen is almost unaltered in magnitude but the first peak occurs somewhat earlier. This indicates that cells in one anatomical location, the lymph nodes, may behave as though they were tolerant while cells in another location, the spleen, behave as though they were immune. The intravenous injection of picryl sulphonic acid causes DNA synthesis in the lymph nodes and spleen. The response in the lymph nodes but not in the spleen is reduced by pretreatment with this agent. This is an example of DNA synthesis following exposure to an antigen which causes unresponsiveness.