Figure 4.

The role of the spleen in parasite clearance and protective immunity. A: Macroscopic observation of spleens from BALB/c mice infected with either 10⁷ wild-type or Δpm4cl6 parasites. This analysis revealed that at 21 days postinfection the spleens of Δpm4-infected mice (lower panel) were much bigger than those from wild-type infected animals (upper panel). This observation was confirmed by comparing the spleen weight in either wild-type or Δpm4cl6-infected mice at different time points (7, 14, 21, and 40 days) after infection. Numbers represent the mean values ± SD of spleen weight of eight animals. B: Cumulative death (left panel) and levels of parasitemia (right panel) of either intact (gray) or splenectomized (black) BALB/c mice infected with 10⁷ Δpm4cl6 parasites. ***P < 0.0001. C: Cumulative death (left panel) of splenectomized Δpm4 convalescent BALB/c mice (convalescent splenectomized [c.s.]) after a challenge with wild-type parasites. As a control Δpm4 convalescent intact BALB/c mice (convalescent not splenectomized [c.n.s.]) and naïve intact BALB/c mice (naïve not splenectomized [n.n.s]) were challenged with the same dose of wild-type parasites. Right panel: Time course of parasitemia in eight individual convalescent splenectomized BALB/c mice (M1–M8) after a challenge with wild-type parasites. None of the Δpm4 convalescent immune mice was able to control the parasitemia when challenged after splenectomy. All mice showed oscillating levels of parasitemia that increased sharply in a few days, leading to the death of the animals. ***P < 0.0001.