Zymosan phagocytosis by Dectin-1 is actin-dependent and requires the ITAM-like motif in the cytoplasmic tail of the receptor. (A) NIH-3T3 cells stably expressing full-length Dectin-1 bind and internalize FITC-labeled zymosan particles (green) through actin-rich phagocytic cups. Actin was visualized by staining with TRITC-labeled phalloidin (red) and phagocytosis was not synchronized. (B) Schematic representation of the constructs used in these experiments demonstrating the position of the various cytoplasmic tail mutations. (C) Comparative binding of FITC-labeled zymosan to NIH-3T3 fibroblasts transduced with selected constructs. (D) FACS-based analysis showing the extent of zymosan internalization by the indicated transductants. The red line indicates the threshold between cells with external or internalized zymosan, as determined by inhibition of uptake with cytochalasin D (CytoD). The data shown are representative of 3 independent experiments.