Fig. 5: Trogocytosis participated in destroying schistosomes by M. fortis macrophages.

a Representative images of macrophages from BALB/c mice and M. fortis showing trogocytic uptake of the schistosomula material. Macrophages from mice and M. fortis were labeled with Cell Tracker Deep Red (red), and the schistosomula was labeled with CDFA-SE (green). Macrophages and parasites were co-cultured at a ratio of 2000 macrophages:1 parasite in the presence of 5% normal mouse or M. fortis serum for 12 h, and the acquisition of labeled parasite material by macrophages (magenta arrows) was visualized by confocal fluorescent microscopy. The images were acquired by Z-stack spanning. The larger images in the middle are shown as a volume view, while the images on the right and below are shown as slices to visualize the inside of the macrophages, representing YZ-axis and XZ-axis, respectively. White arrows indicate the selected typical cell that adhered to the schistosomula. Scale bar, 50 μm. Mouse-MΦ: the macrophages from mouse; Sj: S. japonicum; Mf-MΦ: the macrophages from M. fortis; PP2: the inhibitor of trogocytosis, a potent and selective inhibitor of the src family of tyrosine kinases. b The percentage of macrophages that have taken up schistosomula material. c The number of “bites” of schistosomula material transferred to macrophages was quantified by measuring green fluorescence intensity in the macrophages. d The schistosomula killing rates cultured in the presence of 5% normal mouse or M. fortis serum for 12 h. Data shown are mean ± SEM and repeated thrice with similar results. e Conjugate formation and trogocytosis of macrophages (MΦ) and schistosomula (Sj) after co-culturing for 12 h were visualized by TEM. The mouse macrophages were loosely bound to schistosomula with no evidence of trogocytic invaginations, whereas the M. fortis macrophages were closely bound to schistosomula with trogocytic invaginations (red and blue arrows). Scale bar, 2 μm. f–j Analysis of leukocytes attached to the surface of S. japonicum (f, g), the worm load (h) and the development of S. japonicum (i, j) in vivo after PP2 or vehicle control (5% DMSO, 45% PEG300, 50% PBS) was injected into infected M. fortis at 13 days post-infection. The arrows indicate leukocyte adherence to schistosomes. n = 5–6. Data shown are mean ± SEM and repeated twice with similar results. k SEM images of the trogocytic outcomes on the surface of schistosomula by macrophages (blue arrows) isolated from mouse (Mouse-MΦ) and M. fortis (Mf-MΦ) after incubation for 16 h in the presence of 5% mice or M. fortis serum. S, spine. Yellow arrows show the remaining spines in the epidermis of the schistosomula; magenta arrows show the exposed muscle layer through the bitten-off epidermis of the schistosomula. The whole worm was photographed at 5000× (scale bars, 20 μm); local parts of the worm were photographed at 20,000× (scale bars, 5 μm). l Statistical analysis of the percentage of schistosomula with damaged membrane in vitro from k. m SEM images of the trogocytic outcomes of S. japonicum by leukocytes (blue arrows) in the mouse and M. fortis (Mf) 21 days post-infection. Sj S. japonicum, R ridge, S spine, SP sensory papillae. Red arrows show the exposed muscle layer with the exfoliated epidermis. Scale bars, 10 μm. n Statistical analysis of the percentage of S. japonicum with damaged membrane in vivo from m. o Ultrastructural analysis of mitochondria in schistosomula after incubation with macrophages (either mice or M. fortis) for 12 h in the presence of 5% mice or M. fortis serum. Arrows indicate mitochondria. Scale bars, 0.5 μm. p Statistical analysis of the percentage of damaged mitochondria of schistosomula in vitro from o. q Ultrastructural observation of the mitochondria of schistosomula collected from mice and M. fortis infected with S. japonicum post 13 days. Arrows indicate mitochondria. Scale bars, 2 μm. r Statistical analysis of the percentage of damaged mitochondria of S. japonicum in vivo from q. s Percentage survival of S. japonicum collected from infected BALB/c mice (blue line) and M. fortis (red line) on day 7 post-infection in vitro culture. No cell adhesion and no epidermal damage were found on the surface of worms from both hosts at this stage. t Percentage survival of S. japonicum collected from infected BALB/c mice (blue line) and M. fortis (red line) on day 14 post-infection in vitro culture. No cell adhesion and no epidermal damage were found on the surface of worms from BALB/c mice at this stage. In contrast, the worms from M. fortis have cell adhesion and epidermal damage at this stage. All data are expressed as the mean ± SEM of 4–6 animals per group. Similar results were obtained in at least three repeat experiments.