Figure 6.

Recognition and internalization of spectrin fragments or dead cells by the SCARA1-transfected cells or macrophages. A, HEK293 cells transfected with the full-length hSCARA1 fused with mCherry recognize the SPEC domains of spectrin in the presence of Ca²⁺. SPEC11^e is from erythrocytes and SPEC17–18 is from nonerythrocytes. The mCherry-positive cells were selected for the experiments with GFP, GFP–SPEC11^e, and GFP–SPEC17–18. Nontransfected HEK293 cells (Mock) were used for experiments with GFP–SPEC11^e and GFP–SPEC17–18. B, HEK293 cells transfected with the full-length mSCARA1 fused with mCherry recognize the SPEC domains of spectrin in the presence of Ca²⁺. The mCherry-positive cells were selected for the experiments. C, confocal images show that HEK293 cells transfected with the full-length mSCARA1 fused with mCherry can recognize and internalize the GFP-tagged SPEC domains of spectrin in the presence of Ca²⁺ (scale bars, 10 μm). D, macrophages can bind both SPEC11^e and SPEC17–18 fragments of spectrin, and the binding can be inhibited by the mCL–SRCR fragment of SCARA1. E, macrophages can bind dead cells or debris (ultrasonic-treated) from both erythrocytes and HEK293 cells, and the binding can be inhibited by the mCL–SRCR fragment of SCARA1. Dead cells or debris are pre-stained by anti-spectrin antibodies. F, confocal images show the internalization of spectrin fragments (SPEC11^e and SPEC17–18), dead erythrocytes, and dead Jurkat cells by macrophages. Dead cells or debris are pre-stained by anti-spectrin antibodies. The internalization can be blocked by the mCL–SRCR fragment of SCARA1 (scale bars, 5 μm). G, cartoon representation of dead cell recognition by SCARA1/CD204 via spectrin.