FIG. 4.

Upregulating CD36 increases phagocytosis of RPEs obtained from cryopreserved synchronized cultures and from patient isolates. CD36 wild-type (WT) and CD36-null (KO) murine macrophages were used with cryopreserved synchronized ring-stage parasite cultures (left side) and a fresh patient isolate of ring-stage P. falciparum (right side). Macrophages were treated with 50 μM troglitazone (TRO) or with dimethyl sulfoxide as a control (CTR) for 48 h and then used in RPE phagocytosis assays. Where indicated, RPE suspensions were treated with 50 μg of trypsin per ml and macrophages were treated with 10 μg of anti-CD36 (clone 63) per ml. After incubation and hypotonic lysis to remove noninternalized PEs, macrophages were fixed and stained with Diff-Quik stain and phagocytosis was assessed by light microscopy. Data show a significant increase (**, P < 0.01; Student's t test) in RPE uptake with cryopreserved synchronized RPE cultures (left side, ∼130%) and a patient isolate of RPEs (right side, ∼260%). Blocking CD36 and treating cultures with trypsin significantly reduced phagocytosis of RPEs. In all cases, results are presented as the mean ± the standard deviation of at least four independent experiments. Macrophages were treated with IgG Fc fragments and incubated with RPEs (▪) or subjected to an anti-CD36 blockade (□) or trypsin treatment (▨).