Effect of chloroquine on cellular immune responses of normal and P. knowlesi-infected rhesus monkeys

The immunopharmacokinetics of chloroquine were studied in Plasmodium knowlesi-infected and uninfected rhesus monkeys. In control monkeys, chloroquine depressed the percentage of lymphocyte subpopulation and their proliferative response after the third dose of drug administration. The effect was maximum during day 6 to 10 after initiation of treatment. During this period the plasma level of chloroquine was high. The drug was slowly excreted and recovery in immune functions was noticed by the 20th day of treatment. On the other hand, the drug caused an irreversible effect on the proliferative response of normal lymphocytes following in vitro exposure of cells. Interestingly, while the drug depressed the immune functions of normal animals, it reversed the immunosuppression caused by malarial parasites in infected animals. The probable mechanism of action of the drug has been discussed.