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Contact sensitivity in the mouse. X. Non-specific cytotoxicity of T blasts in the draining lymph nodes.

CBA mice were immunized by painting the skin with the contact sensitizing agent `oxazolone'. The draining lymph nodes were taken at 4 days and mixed with 51Cr-labelled mastocytoma tumour cells. Cytotoxic killing was assessed by the release of 51Cr. Little killing occurred in the absence of phytohaemagglutinin. However, immunized but not normal lymph node cells killed the mastocytoma cells providing phytohaemagglutinin (PHA) was present during the killing reaction. Analysis by the `one hit' hypothesis suggested that up to 14 per cent of the lymphocytes in immunized lymph nodes were effector or killer cells. 
 
The cytotoxicity was non-specific. The evidence for this was that DBA/2 lymph nodes immunized with oxazolone killed DBA/2 mastocytoma cells. The killing reaction did not require macrophages but was due to large cells. These were shown to be θ-positive in carefully controlled experiments. The non-specific cytotoxicity was greatest 4 days after immunization with oxazolone. Reimmunization of the mice on day 10 did not cause a classical secondary response, as assessed by non-specific cytotoxic killing. Instead the time course resembled the primary while the magnitude of killing was slightly reduced. 
 
There were several similarities between non-specific cytotoxic cells and the large pyroninophilic cells and the cells which move to sites of inflammation which are found in lymph nodes immunized with contact sensitizing agents. These similarities included θ-positivity, large size and peak occurrence 4 days after immunization. It is postulated that non-specific cytotoxicity and movement to sites of inflammation are due to blasts or their immediate descendants which originated from T lymphocytes.