FIG. 4.
E1FLAGE2 binding is dependent on cell surface-expressed CD81 and induces cell-cell aggregation. (A) Flow cytometry analysis of binding of anti-CD81 MAb 5A6 (shaded curve) or a mouse IgG1 isotype control (dashed curved) to U937 cells expressing GFP (left side) or CD81-GFP (right side). (B) U937-CD81 (top) or U937-GFP (bottom) cells (1.5 × 105 cells/well) were incubated at 37°C with magnetic beads (10:1 ratio) precoated with H53-captured E1FLAGE2 (C and F), anti-CD81 MAb 5A6 (A and D), or anti-E2 MAb H53 (B and E). Photographs were taken after incubation for 8 h (magnification, ×100). The arrow in the right bottom of part C points to a cell. The arrow in the left top of part C points to one of the magnetic beads (4.5-μm diameter) used for immobilization of the antibodies and proteins.