Unravelling the cytokine network in malaria: reply

Opsonization and phagocytosis of Plasmodium falciparum merozoites measured by flow cytometry

A flow cytometric phagocytosis assay was established to investigate the role of anti-merozoite antibody, complement, and cytokines on the phagocytosis of Plasmodium falciparum merozoites by human neutrophils. This assay involved allowing fluorescein isothiocyanate-labeled merozoites to interact with phagocytes and analysis of the cells on a FACScan with Lysis II software. To differentiate the proportion of neutrophil surface-bound merozoites from the merozoites ingested by neutrophils, the fluorescence of bound merozoites was quenched by adding trypan blue. The data showed that sera from malaria-immune individuals in the Solomon Islands and Papua New Guinea promoted merozoite engulfment by neutrophils. The cytokines tumor necrosis factor alpha, gamma interferon, granulocyte-macrophage colony-stimulating factor, and interleukin-1beta significantly increased the amount and the rate of merozoite phagocytosis by neutrophils. Optimum merozoite phagocytosis occurred when both cytokines and anti-malarial antibody were present.

Cytokines and T-cell response in malaria

The intracellular protozoan Plasmodium sp induces a complex immune response which sometimes implies serious pathological effects for the host. According to in vitro studies and epidemiological surveys, several effector mechanisms are displayed against plasmodial blood stages and a large interaction between humoral and cell-mediated immunity is presumed to occur among protected individuals. The key role of T cells in the antiplasmodial immune response is now well established, but all the regulatory heterogenous mechanisms are not yet fully known. An increasing body of data shows a dual role during malaria attack for some cytokines released by monocytes and macrophages (TNF, IL-1, IL-6) or by T cells (IFN-gamma, lymphotoxin (LT), IL-4). The importance of some plasmodial proteins in the cytokine-induced pathology and the stimulation of a preferential TH1 or TH2 mediated immune response to achieve protective immunity against Plasmodium sp are discussed.