Dynamics of the Major Histocompatibility Complex Class I Processing and Presentation Pathway in the Course of Malaria Parasite Development in Human Hepatocytes: Implications for Vaccine Development

Abstract

Control of parasite replication exerted by MHC class I restricted CD8+ T-cells in the liver is critical for vaccination-induced protection against malaria. While many intracellular pathogens subvert the MHC class I presentation machinery, its functionality in the course of malaria replication in hepatocytes has not been characterized. Using experimental systems based on specific identification, isolation and analysis of human hepatocytes infected with P. berghei ANKA GFP or P. falciparum 3D7 GFP sporozoites we demonstrated that molecular components of the MHC class I pathway exhibit largely unaltered expression in malaria-infected hepatocytes until very late stages of parasite development. Furthermore, infected cells showed no obvious defects in their capacity to upregulate expression of different molecular components of the MHC class I machinery in response to pro-inflammatory lymphokines or trigger direct activation of allo-specific or peptide-specific human CD8+ T-cells. We further demonstrate that ectopic expression of circumsporozoite protein does not alter expression of critical genes of the MHC class I pathway and its response to pro-inflammatory cytokines. In addition, we identified supra-cellular structures, which arose at late stages of parasite replication, possessed the characteristic morphology of merosomes and exhibited nearly complete loss of surface MHC class I expression. These data have multiple implications for our understanding of natural T-cell immunity against malaria and may promote development of novel, efficient anti-malaria vaccines overcoming immune escape of the parasite in the liver.

Malaria and the liver: immunological hide-and-seek or subversion of immunity from within?

“…Mouse primary hepatocytes have also been shown to be able to process Plasmodium berghei CSP after live sporozoite infection, and present CSP-derived peptides to specific CD8 T cells in vitro in a proteasome-dependent manner (Bongfen et al, 2007 ). A recent study (Ma et al, 2013 ) performed using human primary hepatocytes has also confirmed that the direct MHC class I presentation pathway is not markedly affected by live P. berghei sporozoites: mRNA expression levels of all major components of the MHC class I processing and presentation machinery were not significantly affected by parasite replication at 24 or 48 h post-infection, while the levels of MHC class I expression were decreased only by 10–20% at the surface of infected host cells as compared to either uninfected or untreated controls. Furthermore, ectopic expression of CSP did not interfere with basal MHC class I expression, or IFN-γ and TNF-α-induced upregulation of MHC class I expression (Ma et al, 2013 ).…”

Cytotoxic Markers Associate With Protection Against Malaria in Human Volunteers Immunized WithPlasmodium falciparumSporozoites

“…So-called classic cytotoxic CD8 T cells can be activated by malaria parasite antigen on infected hepatocytes via major histocompatibility complex (MHC) class I [ 25 ] and are associated with protection in a number of (animal) models [ 13 , 14 , 26 ]. CD8 T cells are involved in protection in the murine CPS and RAS models [ 27 – 29 ], but their precise effector mechanisms remain subject of debate.…”

Virtual Screening and Experimental Validation Identify Novel Inhibitors of the Plasmodium falciparum Atg8–Atg3 Protein–Protein Interaction

“…P. falciparum 3D7HT‐GFP parasite strain was propagated in the Parasitology Core facility of the Johns Hopkins Malaria Research Institute. In vitro infection of human hepatocytes, and detection and quantification of P. falciparum 3D7HT‐GFP EEFs by flow cytometry were performed as previously described …”