Spleen function in quartan malaria (due to Plasmodium inui): evidence for both protective and suppressive roles in host defense.

For investigation of the role of the spleen in host defense and chronicity in quartan malaria, the course of Plasmodium inui infection was studied in 39 intact rhesus monkeys, 16 monkeys splenectomized before infection, and 22 monkeys splenectomized after infection. Splenectomized animals consistently had peak parasitemias greater than 10-fold higher than those of intact animals, but the mortality rate at peak parasitemia was only higher in monkeys splenectomized before infection. Whereas intact animals had persistent infections for one to 13 years, splenectomized animals achieved self-cure (persistently negative blood smears for three or more months) within less than a year. These observations suggest that the spleen exerts a protective role during the acute stage and a suppressive role during the chronic stage of quartan malarial infection.