Figure 4From: C-reactive protein does not opsonize early apoptotic human neutrophils, but binds only membrane-permeable late apoptotic cells and has no effect on their phagocytosis by macrophagesCRP binds to a subpopulation of apoptotic neutrophils. (a) Three color flow cytometry demonstrated that FITC-CRP (50 μg/ml) bound strongly to a subpopulation of apoptotic neutrophils that also stained with propidium iodide (PI). (b) Immunofluorescence microscopy of aged human neutrophils revealed strong CRP binding (green) to a late apoptotic neutrophil (arrow)(left panel). Nuclei have been stained with TO-PRO-3 (blue). The late apoptotic cell has almost no residual nuclear staining (right panel). There was no detectable binding to an early apoptotic neutrophil (arrowhead) or to non-apoptotic neutrophils. (c) Light microscopy of CRPhigh (left panel) and CRPlow (right panel) cells sorted by FACS from a population of aged neutrophils illustrates the ghost-like morphology of CRP-binding apoptotic neutrophils. The CRPlow cells comprise a mixture of non-apoptotic and early apoptotic neutrophils.Back to article page