Figure 6.

Effect of serum, Factor H (FH) and C4-binding protein (C4BP) on the entry of Escherichia coli and Group B Streptococcus (GBS) into THP-1 cells or THP-DM. E. coli (a) or GBS (b) were incubated with 40% adult serum (AS) or cord serum (CS), puri- fied Factor H (FH) or C4-binding protein (rC4BP or C4BP-PS) (25 μg/ml) for 15 min, washed, and then further incubated with either THP1 cell suspension or THP-DM monolayers at a multiplicity of infection of 1 : 10. Heat-inactivated (HI) serum was also included as a negative control. After incubation, the cells were washed and further incubated with gentamicin-containing medium (100 mg/ml) for 1 hr to kill extracellular bacteria. Numbers of internalized bacteria were determined by plating on blood agar and expressed as per cent invasion with respect to control bacteria (incubated with neither sera nor purified proteins). Experiments were conducted at least three times and the data are presented as means ± SD. The survival of the bacteria, treated with serum or purified proteins, was considered significantly increased or decreased when compared to untreated controls. **P < 0.05 by two-tailed t-test.