FIGURE 2.

C-terminal SCR19–20 of Factor H is the key co-factor in Factor H-mediated pneumococcal adherence to and invasion into host cells. A, adherence of Factor H-coated pneumococci to A549 cells was determined in the presence of mAbs M14, CO2, or C18 (each 2 μg ml⁻¹ per well) or absence of a mAb (control). The antibodies bind to the middle region (M14), SCR19 (CO2), or SCR19–20 (C18) of Factor H. Results are shown as relative adherence of Factor H-bound pneumococci compared with untreated pneumococci. *, p < 0.02; ns, not significant. B, invasion and intracellular survival of Factor H-coated pneumococci in the presence of monoclonal antibodies M14, CO2, or C18 (each 2 μg ml⁻¹) were determined by the antibiotic protection assay. Results show the relative invasion of pneumococci into A549 cells compared with Factor H-treated bacteria and in the absence (control) of monoclonal antibodies. *, p < 0.02; ns, not significant.