IGHG3 and parasitic infectious disease: These were also the sites with the highest levels of artemisinin-resistant P. falciparum. Seroprevalences of IgG3, complement fixation, and opsonic phagocytosis of merozoites were associated with a faster PC1⁄2, a reduced odds of having a PC1⁄2 of ≥5 hours, and having parasitemia 3 days after starting artesunate treatment.