Fig. 1: Malarial antibodies induce merozoite-phagocytosis by neutrophils and monocytes.

a Percentage of individual leukocytes in PBLs from Danish blood donors (n = 10) was enumerated by flow cytometry. Horizontal lines represent median values. b From each donor, 6 × 10⁴ PBLs were incubated with unopsonized merozoites (UOP), merozoites opsonized with a pool of nonimmune plasma (NIP), or with immune plasma (IP) for 30 min at 37 °C for phagocytosis to occur. Cells were stained with anti-CD14, CD16, CD45, and CD66b antibodies and analyzed by flow cytometry to enumerate ethidium bromide (EtBr)-positive cells. The mean number (no.) of neutrophils (blue) and monocytes (red), which ingested merozoites are shown in the upper panel, and the percent contribution of neutrophils and monocytes to overall PBL phagocytosis is shown in lower panels for the given opsonized/unopsonized condition. c Mean percentage of monocytes or neutrophils in PBL preparations that phagocytosed merozoites in the presence of NIP, IP, or UOP condition. The percent phagocytosis of IP-opsonized merozoites is also shown for cytochalasin D (Cyt D) treated PLBs. d Kinetics of IP-opsonized merozoite uptake by monocytes and neutrophils present in Cyt D pretreated or untreated PBLs. Phagocytosis was stopped at indicated time points, and percent phagocytosis by the neutrophils and monocytes is expressed as the mean of triplicates. Data are represented from one of the two independent assays. Results were obtained with PBLs from 10 different Danish blood donors (a–c). P values were determined by Wilcoxon signed-rank test b and c. Asterisks represent P values (**P < 0.01).