Mechanism of neutrophil dysfunction by Plasmodium falciparum secreted histidine-rich protein II

People with malaria infection caused by Plasmodium falciparum are significantly more susceptible to invasive bacterial infections during and in the weeks following acute malaria infection. Plasma from infected patients can modulate neutrophil function, a critical aspect of the immune response for controlling bacterial infection. Interestingly, neutrophils isolated from children with malaria have an impaired oxidative burst even at 4 weeks following malaria infection. Proposed models of neutrophil dysfunction suggest a role for heme induction of heme oxygenase 1, an enzyme known to reduce the production of reactive oxygen species in neutrophils by down- regulating expression of NADPH oxidase subunits. However, heme does not remain elevated after malaria infection and does not explain the persistent neutrophil dysfunction. Here a model is proposed that incorporates histidine-rich protein II (HRPII), an abundant secreted parasite protein that circulates as a nanoparticle. Notably, HRPII has a long half-life and persists in children with malaria for up to 4 weeks. It was previously shown that heme-laden HRPII (HRPII:heme) delivers a high load of intracellular heme, inducing reactive oxygen species (ROS), inflammation, and cellular junction disruption in vascular endothelial cells and causes vascular leakage in mice. In preliminary studies using a model human neutrophil-like cell line (dHL60), it has been found that HRPII:heme, unlike free heme, does not directly stimulate the oxidative burst. Pre-treatment with HRPII:heme prior to dHL60 stimulation with PMA results in decreased oxidative burst within a few minutes. It also causes a slow but dramatic induction of heme oxygenase 1. The first aim utilizes targeted molecular blockade in dHL60 cells of known pathways of HRPII cellular effects and neutrophil pathways involved in oxidative burst signaling. The second aim will utilize an unbiased approach with transcriptome profiling (RNA-seq) of dHL60 treated with HRPII and a genome-wide CRISPR/Cas9 knockout screen to determine genes essential for HRPII effects. The proposed work will provide insight into how HRPII affects neutrophils and, in time, potential therapeutics to prevent invasive bacterial infections in patients with malaria.

NIH Project details

Basic Science

Jul 2024 — May 2026

$209,925

United States