Restimulation of PPD‐stimulated Lymphocytes: Decreased Responsiveness of Prestimulated Cells to a Second Challenge with PPD and PHA

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Abstract
[Human] lymphocytes stimulated with purified protein derivative (PPD) were inhibited in their response to a 2nd stimulation with PPD or phytohemagglutinin (PHA). The degree of inhibition was related to the PPD concentration during pre-stimulation, the dose-response curve for inhibition resembling very much that of stimulation. The decreased reactivity was neither due to a toxic effect of PPD nor to altered proliferation kinetics of the prestimulated cells. Lymphocytes preincubated for 6 h or 16 days with PPD were equally refractory, and the non-reactivity persisted even if the cells were incubated without stimulant for 1 wk or more. The pre-stimulated cells suppressed the PHA stimulation of fresh lymphocytes. The decreased reactivity of the pre-stimulated lymphocytes may be due to the action of suppressor lymphocytes generated during the primary stimulation.