The Use of Filter-Purified Merozoites to Assess Anti-Merozoite Immunity

The role of complement during the invasion of red blood cells by Plasmodiummerozoites is an enticingfield of study that has great potential to impact not just our overall understanding of how the parasite interacts with the human host but also guide future efforts in the development of efficacious malarial vaccines. The complexity of parasite and host interactions during the invasion of red blood cells (RBCs) by the merozoites and the subsequent growth within the newly invaded host cell has led to conflicting results in the literature. We have recently reported the enhancing effects of anti-merozite antibodies and complement interactions at promoting red blood cell invasion and growth by merozoites.Wehave observed this enhancement using both a traditional invasion assay and the Plasmodium berghei ANKA model of experimental malaria (Biryukov et al., 2016). Our results are in contradiction to those reported by Boyle et al. (Boyle et al., 2015) who found that in the presence of complement, anti-merozoite antibodies are effective in preventing RBC invasion. We attributed these discrepancies in part to the fact that Boyle et al. usefilter-purifiedmerozoites as opposed to naturally egressedmerozoites and argue that filter-purifiedmerozoites are defective and more susceptible to complement attack. In their letter to the editor, Boyle and Beeson argue that the discrepancy between our results and theirs cannot be attributed to defectivemerozoites. Wewould like to thank Boyle and Beeson for taking the time to read our article and for providing stimulating discussion. We take this opportunity to reply to their comments. Boyle and Beeson argue that a recent report by Sack et al. (Sack et al., 2015) using late arresting genetically attenuated parasites (LAGAP) supports the role of antibodies and complement in controlling parasitemia. In this study, the authors report that immunization with LAGAP induces antibodies against blood stage parasites. Use of cobra venom factor (CVF) resulted in decreased efficacy of immunization.