title: Transcription and expression of Plasmodium falciparum histidine-rich proteins in different stages and strains: implications for rapid diagnostic tests.
abstract: BACKGROUND
  Although rapid diagnostic tests (RDTs) for Plasmodium falciparum infection that target histidine rich protein 2 (PfHRP2) are generally sensitive, their performance has been reported to be variable. One possible explanation for variable test performance is differences in expression level of PfHRP in different parasite isolates.
  
  
  METHODS
  Total RNA and protein were extracted from synchronised cultures of 7 P. falciparum lines over 5 time points of the life cycle, and from synchronised ring stages of 10 falciparum lines. Using quantitative real-time polymerase chain reaction, Western blot analysis and ELISA we investigated variations in the transcription and protein levels of pfhrp2, pfhrp3 and PfHRP respectively in the different parasite lines, over the parasite intraerythrocytic life cycle.
  
  
  RESULTS
  Transcription of pfhrp2 and pfhrp3 in different parasite lines over the parasite life cycle was observed to vary relative to the control parasite K1. In some parasite lines very low transcription of these genes was observed. The peak transcription was observed in ring-stage parasites. Pfhrp2 transcription was observed to be consistently higher than pfhrp3 transcription within parasite lines. The intraerythrocytic lifecycle stage at which the peak level of protein was present varied across strains. Total protein levels were more constant relative to total mRNA transcription, however a maximum 24 fold difference in expression at ring-stage parasites relative to the K1 strain was observed.
  
  
  CONCLUSIONS
  The levels of transcription of pfhrp2 and pfhrp3, and protein expression of PfHRP varied between different P. falciparum strains. This variation may impact on the detection sensitivity of PfHRP2-detecting RDTs.
authors.affiliation: Department of Drug Resistance and Diagnostics, Australian Army Malaria Institute, Gallipoli Barracks, Enoggera, Queensland, Australia.
authors.forename: Joanne
authors.initials: J
authors.lastname: Baker
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Gatton
authors.forename: Jennifer
authors.initials: J
authors.lastname: Peters
authors.forename: Mei-Fong
authors.initials: MF
authors.lastname: Ho
authors.forename: James S
authors.initials: JS
authors.lastname: McCarthy
authors.forename: Qin
authors.initials: Q
authors.lastname: Cheng
mesh_terms: D000818:Animals; D000953:Antigens, Protozoan / Q000235:genetics* / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D008018:Life Cycle Stages / Q000235:genetics*; D016778:Malaria, Falciparum / Q000175:diagnosis*; D010963:Plasmodium falciparum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism*; D011634:Public Health; D012680:Sensitivity and Specificity; D013045:Species Specificity; D014158:Transcription, Genetic
chemical_list: D000953:Antigens, Protozoan; C514457:HRP-2 antigen, Plasmodium falciparum; D015800:Protozoan Proteins