Mutant/mutation
The mutant expresses HRP2 from P. falciparum (3D7 strain; PF3D7_0831800). The hrp2 gene is under control of the constitutive hsp70 promoter and the expression cassette is introduced into the 230p neutral locus

Protein (function)
Plasmodium falciparum is the only human Plasmodium species that produces PfHRP2 with expression throughout the asexual intraerythrocytic cycle and early stages of gametocytogenesis. Each parasite produces approximately 2–10 femtograms of PfHRP2 per 48 h replication cycle, but only 3% of PfHRP2 produced is retained by the parasite, localizing to the parasite cytoplasm or food vacuole. The remaining 97% is exported into the infected RBC (iRBC) cytoplasm, concentrating in packets near the iRBC membrane. PfHRP2 can also be secreted from intact iRBCs, but the majority (> 90%) is released when mature schizonts rupture the iRBC to release merozoites. Following release, PfHRP2 can be detected in various bodily fluids including whole blood, RBCs, plasma, serum, urine, cerebral spinal fluid, and saliva. However, the physiological function of PfHRP2 and the significance of its localization are unknown. Experimental evidence indicates PfHRP2 can promote coagulation, interfere with immune cell activation, and may contribute to cerebral malaria pathology by disrupting barrier integrity in the brain.

Phenotype
PfHRP2 expression in blood stages. Evidence is presented for export into the host red blood cell (similar to export of HRP2 in P. falciparum infected red blood cells)

From the Abstract:
'Transgenic PbPfHRP2 parasites in BALB/c mice produced and exported tgPfHRP2 to the RBC cytosol similar to P. falciparum. As in humans, tgPfHRP2 levels were found to be approximately 20-fold higher within the RBC fraction than the plasma post-treatment. RBC localized tgPfHRP2 persisted longer than tgPfHRP2 in the plasma after curative treatment. tgPfHRP2 positive, but DNA negative once-infected RBCs were also detected in mouse peripheral blood for 7–9 days after curative treatment.'

'The data suggest that persistence of PfHRP2 is due to slower clearance of protein from the RBC fraction of the whole blood. This appears to be a result of the presence PfHRP2 in previously infected, pitted cells, as opposed to PfHRP2 binding naïve RBCs in circulation post-treatment.'

Additional information
From the paper: 'Western blot analysis confirmed the presence of tgPfHRP2 in the iRBCs. tgPfHRP2 was detected in the RBC cytosolic fraction after saponin lysis, suggesting it was exported into the iRBC cytoplasm. Immunofluorescence microscopy on PbPfHRP2 iRBCs was performed using monoclonal antibodies against PfHRP2 and Plasmodium enolase, a known parasite-localized protein, to differentiate the parasite from the iRBC cytoplasm. In this assay, tgPfHRP2 localized to both the parasite and iRBC cytoplasm. Importantly, the PfHRP2 staining observed in PbPfHRP2 iRBCs mimicked the staining of P. falciparum iRBCs. PfHRP2 was not detected in negative controls, including RBCs infected with the P. berghei ANKA wild-type strain that does not express PfHRP2 and uninfected RBCs.'

Other mutants