Cell‐mediated immune reactions in vitro: Cytotoxicity of lymphocytes activated by phytohemagglutinin and anti‐immunoglobulin serum

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Abstract
Rabbit lymphocytes were activated by phytohemagglutinin (PHA) and/or an antiserum against rabbit IgG obtained in a goat (GARIG serum). Both stimulants induced cytotoxicity in lymphocytes. The destruction of target cells was followed by measuring 51Cr release from labeled fowl erythrocytes. The kinetic analysis of the target cell destruction exhibited striking differences.Following activation with PHA the lysis of the target cells started immediately after the addition of the stimulant and proceeded linearly. With GARIG serum as the activating agent the lysis started after a latent period of 20 h which was the same when the lymphocytes were preincubated with Garing serum for 20 h before the labeled erythrocytes were added. After the lysis had started it proceeded in sigmoidal fashion.When given numbers of lymphocytes were mixed with varying numbers of target cells the maximum velocity of target cell destruction was reached at a ratio of one lymphocyte to one target cell during activation with PHA and at a ratio of five lymphocytes to one target cell during activation with GARIG serum. Using concentrations of target cells at which maximum velocity of target cell destruction occured there was a linear relation between the number of added lymphocytes activated by GARIG serum and the degree of the lysis.Activation of the lymphocytes simultaneously with PHA and GARIG serum resulted in a marked enhancement of the target cell destruction which by far exceeded the sum of the cytotoxicity when the lymphocytes were activated separately.