FIG. 2.
In transfected CHO cells, association with bacteria is specific for SR-A, independent of the presence of serum, and sensitive to temperature. (A) CHO cells stably transfected with hSR-AI or hSR-AII were incubated with FITC-labelled E. coli K-12 or DiIAcLDL (inset) for 45 min. Binding to SR-A was blocked by poly(I) and SR-A ligands on the bacteria were blocked by preincubating the FITC-labelled E. coli K-12 with a rabbit-anti-E. coli K-12 polyclonal antiserum. The difference detected between CHO hSR-AI and CHO hSR-AII incubated with E. coli alone is significant (P < 0.01), but the difference after incubation with poly(I) is not (P > 0.05). The levels of DiIAcLDL endocytosis are shown in the inset. The fluorescence obtained for CHO WT (–·–·–); CHO hSR-AI (––––), and CHO hSR-AII (–) populations incubated with DiIAcLDL is shown. (B) CHO transfectants and control cells were incubated in the presence or absence of 10% heat-inactivated FCS and analyzed by flow cytometry. The difference in E. coli uptake by CHO WT in the presence and absence of serum is not significant (P > 0.1). (C) CHO cells stably transfected with SR-A were incubated with heat-killed FITC-labelled S. aureus (200 bacteria per CHO cell) for 45 min at 37°C in the presence or absence of poly(I) or its cognate non-SR-A ligand, poly(C). (D) CHO hSR-AI, CHO hSR-AII, and CHO WT cells were incubated with heat-killed FITC-labelled E. coli (100 bacteria per CHO cell) at 4 or 37°C and were analyzed as in Fig. 1. The difference detected between CHO WT cells incubated at 4 or 37°C is not significant (P > 0.15).