Naturally acquired IgM binds to Pf antigens with high affinity, inhibits growth of Pf parasites in vitro, and enhances phagocytosis of Pf merozoites. (A) CD19+ CD20+ IgD− CD10− CD27+ IgM+ B cells were bulk sorted for immortalization, followed by single-cell sorting of immortalized Pf+ B cells for continuous cell culture. An initial screen identified both PfAMA1- and PfMSP1-binding clones. IFAs were performed with affinity-purified culture supernatant-derived PfAMA1-specific IgM (clones A24, B11, H21, and K15, and negative control clone of unrelated specificity). Pf 3D7 schizonts were stained with IgM (green, first column) and costained with anti-hsp70 antibody (purple, second column) and the nuclear stain DAPI (blue, third column). Images are representative of at least two independent experiments. Scale bar, 5 μm.

Hopp CS, Sekar P, Diouf A, Miura K, Boswell K, Skinner J, Tipton CM, Peterson ME, Chambers MJ, Andrews S, Lu J, Tan J, Li S, Doumbo S, Kayentao K, Ongoiba A, Traore B, Portugal S, Sun PD, Long C, Koup RA, Long EO, McDermott AB, Crompton PD. Plasmodium falciparum-specific IgM B cells dominate in children, expand with malaria, and produce functional IgM. J Exp Med. 2021 218(4):e20200901.