Extraction of P. falciparum and pitting of infected red cells by THP-1 monocytes. Trophozoite infected human group O+ red cells (1 × 106) in RPMI 1640 medium were co-incubated with TNF-α activated THP-1 monocytes (3 × 106) for 1 hour at 37°C. Giemsa stained thin smears of the cultures were prepared and examined under oil immersion using ×100/1.3 objective of an Olympus microscope (Olympus America, NY). Pitting was preferred to erythrophagocytosis (panel A). The photomicrographs show monocytes with six pitted malaria parasites (B), phagocytosed infected RBCs (C) and spherocytic RBCs (D, arrow). Photomicrographs were captured using an Olympus MagnaFire camera (Olympus America, NY) using MagnaFire acquisition software.