Abstract
Many of the monkeys sensitized with schizont-infected cells in Freund's complete adjuvant (FCA) survived challenge with homologous Plasmodium knowlesi. In view of the ability of FCA to promote induction of cell-mediated immunity, evidence was sought of delayed hypersensitivity and lymphocyte sensitization in monkeys which survived infection. The results of three groups of experiments are presented: (1) skin tests by intradermal injection of parasitized erythrocytes into chronically infected and FCA-immunized monkeys; (2) in vitro thymidine uptake (as a measure of DNA synthesis) by spleen and lymph node cells from sensitized and sensitized and challenged monkeys in the presence of specific and nonspecific antigens; and (3) measuring the release of 51Cr label from parasitized cells in the presence of immune and normal spleen cells. Examination of the intradermal injection sites revealed immediate reactions in both chronically infected monkeys and in monkeys sensitized with schizont-infected cells in Freund's adjuvant; in the former the immediate reaction increased with the duration of the infection. In the FCA-sensitized monkeys there was evidence of a delayed-type response. Both spleen and lymph node cells from FCA-sensitized monkeys were responsive in terms of increased DNA synthesis in vitro to the sensitizing antigen. This correlates with delayed hypersensitivity. No specific cytotoxic activity of immune spleen cells from FCA-sensitized or chronically infected monkeys on parasitized cells could be detected. A model system using sheep red cells gave positive results. Although these results suggest that in the FCA-sensitized monkeys there is a delayed hypersensitivity to malarial antigens, we do not know if this is involved in the protective mechanisms associated with sensitization with schizontinfected cells in Freund's complete adjuvant.
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