Fig. 1: Neutrophils predominately mediate opsonic phagocytosis of CSP-coated beads and sporozoites in whole blood.

A CSP-coated beads were opsonized with different concentrations of rabbit anti-CSP IgG. Neutrophils showed greater phagocytosis activity compared to monocytes (P < 0.001, two-way ANOVA). Bars represent the mean and standard error from six independent experiments. B CSP-coated beads opsonized with rabbit anti-CSP IgG (1/500 dilution), were co-incubated at different ratios with whole leukocytes. Phagocytosis activity was substantially higher by neutrophils than monocytes (P < 0.001, two-way ANOVA). Bars represent the mean and standard error from three independent experiments. C Phagocytosis of sporozoites was tested using a transgenic PfCSP-P. berghei sporozoite line, opsonized with pooled immune sera from Kenyan adults. In the presence of immune antibodies, more sporozoites were phagocytosed by neutrophils (dark-blue bar) than monocytes (light-blue bar). Bars represent the mean and range from two independent experiments. D The number of beads phagocytosed by each monocyte subset was quantified and standardised as beads per 100 monocytes. The classical monocyte subset showed greater phagocytic activity (P < 0.001, one-way ANOVA). Bars represent the mean and standard error from five experiments. E Opsonization of P. falciparum sporozoites with a pool of malaria-exposed Kenyan adult sera induced a higher level of phagocytosis by neutrophils compared to unopsonized control. Opsonic phagocytosis activity was expressed as the percentage of ethidium bromide-positive cells. Bars represent the mean and range from two experiments. F Effect of depleting CSP-specific antibodies from a pool of malaria-exposed Kenyan adult sera on opsonic phagocytosis of P. falciparum sporozoites by neutrophils. Depletion of CSP-specific antibodies reduced opsonic phagocytosis by 70% (Man–Whitney test, P = 0.028). Bars represent the mean and standard error from four experiments. G mAb MGG4 (IgG1) was isolated from an individual exposed to P. falciparum sporozoites and was tested for promoting opsonic phagocytosis by neutrophils. Opsonic phagocytosis was significantly higher compared to a control mAb (2A10), which binds to the same epitope, but was modified (LALA mutations in the Fc region) to reduce FcγR binding (Mann–Whitney test P = 0.012). Bars represent the mean and standard error from three experiments.