PfHP1 depletion induces gametocyte conversion. Distinction between 3D7/HP1OFF early gametocytes and arrested trophozoites by IFA (left) and proportion of Pfs16/KAHRP-positive parasites in 3D7/HP1ON and 3D7/HP1OFF (right). Values show the mean ± SD of three biological replicates (100 KAHRP-pos. iRBCs were scored per experiment). (D) a-Pfs16 IFA of a 3D7/HP1OFF parasite culture (Shield-1 removal at 4–12 hpi) at 32–40 hr postreinvasion (image taken at 40X magnification). The gametocyte hyperinduction phenotype is highlighted by the high proportion of Pfs16-positive stage I gametocytes among all DAPI-positive iRBCs. (C) Growth-arrested 3D7/HP1OFF parasites reenter mitotic proliferation after Shield-1 replenishment. dpi, days postreinvasion. PfHP1 depletion causes reversible cell-cycle arrest at the G1/S transition phase. Lower right panel: a-PfHP1/a-PfEMP1 (mAb 6H1) IFAs of 3D7/HP1ON and 3D7/HP1OFF parasites at 16–24 hpi in generation 2. PfEMP1 in 3D7/HP1OFF parasites at the single-cell level is hyperexpressed and correctly trafficked to the iRBC surface

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