Fig. 4.

Effect of complement on IC-induced down-regulation of MHC class II. (a) IC were formed and then incubated with medium, normal or heat-inactivated (56°C, 30 min) human serum, for 1 h at 37°C. (b) IC were formed in the presence of medium, normal or heat-inactivated (56°C, 30 min) human serum, for 1 h at 37°C. Then, for both experimental conditions, human monocytes (0·5 × 10⁶ cells/ml) were incubated with medium (control) or the IC preparations indicated above for 18 h. After this period, human monocytes were stained with an anti-HLA-DR antibody and the level of expression of MHC class II was evaluated by flow cytometry. Data are expressed as % MFI ± s.e.m. of control cells. Statistical significance was calculated using the Mann–Whitney test, two-tailed; n= 8. *P < 0·01 significantly different from control.