Fig. 3: Bb and C3b are deposited on the surface of T. brucei gambiense in a C2-independent manner, while C4b and C5b are not detected by immunofluorescence.

Representative fluorescence micrographs of trypanosomes incubated in depleted or complete human serum tested for deposition of complement factors using fluorescently-labelled antibodies as indicated (red = AF594, green = FITC; blue = DAPI stain; left images are merged with brightfield channel; scale bar = 2 μm). Independent experiments were performed at least in triplicate. Note, that even at low temperatures, molecules bound to the trypanosome surface are rapidly internalised, accumulating in the flagellar pocket before delivery to the early endosome. Flagellar pocket, early endosome and lysosome are highlighted by white arrows on selected images. a T. b. gambiense in C2-depleted serum (no CP/LP) stained with anti-Bb. Bb was robustly detected at the flagellar pocket. b T. b. gambiense (left) in complete serum and sensitised sheep erythrocytes (right, positive control) in C6-depleted serum (no MAC assembly) stained with anti-C4. No C4b-specific signal was detected on trypanosomes. c T. b. gambiense in C2-depleted serum (no CP/LP) stained with anti-C3. C3b was robustly detected at the flagellar pocket. d T. b. gambiense in fB-depleted serum (no AP) stained with anti-C3. No C3b-specific signal was detected. e T. b. gambiense (left) in complete serum and sensitised sheep erythrocytes (right, positive control) in C7-depleted serum (no MAC assembly, but C5b-6 membrane deposition) stained with anti-C5. No C5b-specific signal was detected on trypanosomes. For additional experiments, replicates and controls, see Supplementary Fig. 4.