Histidine-rich protein 2 (HRP2)

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The HRP2 antigen - practicalities P.falciparum parasites produce “histidine-rich” proteins (HRP). The HRP2 antigen is highly expressed and stable, and is therefore very useful in the detection of P.falciparum infection. Additionally, antibodies that detect HRP2 also cross react with the closely related HRP3 protein which can improve their sensitivity, particularly where HPR2 is not expressed. At a high parasitaemia the sensitivity of HRP2 (like LDH-based tests) will meet or exceed 90% detection for P.falciparum. However, at lower parasite levels (<1000 parasites/μL) the sensitivity is significantly less (around 70% for HRP2, which may perform better than LDH at low parasite levels). Characteristics of HRP2 to be aware of (1) Half-life: HRP2 has a long half-life in vivo and its expression persists following successful treatment. It should not therefore be used to monitor disease resolution since HRP2 protein persists for several weeks post-therapy see antigen clearance after successful resolution. (2) HRP2 may be affected by the prozone effect (3) HRP2 is increasingly subject to gene deletion in some geographical areas* which may cause false negative results.