Using anti-θ serum, we obtained a population of spleen cells which was deficient in T-cell activity but, by all the tests applied, was unaffected in B- or A-cell activity. The response of this population was reconstituted, in vitro, by suspensions of cells known to be enriched in T-cell activity and containing few, if any, B- or A-cells. Supernatants from cultures containing appreciable numbers of T-cells incubated with antigen were also able to reconstitute this T-cell-depleted population. We speculate that these supernatants contain activity which replaces at least some of the normal T-cell function in the initiation of an immune response.

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This work was supported by the National Cancer Institute of Canada and the Medical Research Council (Grant MA-3017).

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