Species-restricted adhesion of RBCs to human SIRPα1ex-coated surfaces. (A) RBCs from 5 mammalian species were allowed to adhere to either human SIRPα1ex- or GST-coated wells (∼10 000 molecules/μm2) and the fraction of well area covered by adherent RBCs after centrifugation was determined. Adhesion results closely matched the results from the flow cytometry-based SIRPα1ex binding assay. Only RBCs from human and pig showed significant adhesion to SIRPα1excoated wells among the species tested. The ratio of RBC area coverage on SIRPα1ex to that on GST is indicated. (B) Human and rat RBCs are probed using atomic force microscopy using human SIRPα1ex-coated tips, leading to almost 100% adhesion with human cells. Almost no adhesion is seen with rat cells. The force required to disrupt single bonds of CD47-SIRPα is approximately 70 pN. See Document S1 and Figures S1-S3 for details on AFM experiments. Error bars represent 1 SD from multiple experiments.
