Figure 6.

Inhibition of the C3 convertase by Compstatin reduces phagocytosis of zymosan dramatically in whole blood leukocytes. Whole blood treated with 50 µM Compstatin 15 min before the exposure to the phagocytosis targets presented significantly reduced phagocytosis in all assessed subtypes. Compstatin-treated neutrophils showed massively reduced phagocytotic activity at any given time point (A, *** P < 0.001). In classical monocytes (B), the difference to an untreated control for Zymosan-positive cells was the lowest at 5 min time-point (** P < 0.01), with only minor change over time in the Compstatin-treated specimen, resulting in an increase of difference (*** P < 0.001 for 10, 15, and 20 min). Non-classical monocytes (C) showed a similar tendency with the 5 min time-point not significant (P > 0.05), but the following time-points with increasing significant differences to the untreated control (* P < 0.05 for 10 min and ** P < 0.01 for 15 and 20 min). The results are presented as means and S.E.M. and P values were calculated with ANOVA and Tukey post hoc test, n = 3, *, ** and *** P < 0.05, < 0.01 and < 0.001, respectively. (D) shows representative results from phagocytosis by PMNs at the 15 min time-point (E). The overall substantial role in the phagocytosis of zymosan-particle by monocytes was verified by confocal fluorescence microscopy in normal human serum and heat-inactivated serum, respectively. After 45 min of phagocytosis, cells without functioning complement showed significantly less engulfed zymosan (red). Scale bar indicates 20 µm.