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. We propose a model 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. We previously showed 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), we have 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 goal of this proposal is to identify the molecular
mechanisms by which neutrophils sense HRPII:heme and the signaling pathways that are required to impair
oxidative burst activity. Our first aim utilizes targeted molecular blockade in dHL60 cells of known pathways of
HRPII cellular effects and neutrophil pathways involved in oxidative burst signaling. Our 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.
